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Bertinetti A, Garcia T, Palmer B, Rodrigues M, Bradshaw T, Vija AH, Culberson W. Active and passive dosimetry for beta-emitting radiopharmaceutical therapy agents in a custom SPECT/CT compatible phantom. Phys Med Biol 2024; 69:115031. [PMID: 38684165 DOI: 10.1088/1361-6560/ad450c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2023] [Accepted: 04/29/2024] [Indexed: 05/02/2024]
Abstract
Objective. This work introduces a novel approach to performing active and passive dosimetry for beta-emitting radionuclides in solution using common dosimeters. The measurements are compared to absorbed dose to water (Dw) estimates from Monte Carlo (MC) simulations. We present a method for obtaining absorbed dose to water, measured with dosimeters, from beta-emitting radiopharmaceutical agents using a custom SPECT/CT compatible phantom for validation of Monte Carlo based absorbed dose to water estimates.Approach. A cylindrical, acrylic SPECT/CT compatible phantom capable of housing an IBA EFD diode, Exradin A20-375 parallel plate ion chamber, unlaminated EBT3 film, and thin TLD100 microcubes was constructed for the purpose of measuring absorbed dose to water from solutions of common beta-emitting radiopharmaceutical therapy agents. The phantom is equipped with removable detector inserts that allow for multiple configurations and is designed to be used for validation of image-based absorbed dose estimates with detector measurements. Two experiments with131I and one experiment with177Lu were conducted over extended measurement intervals with starting activities of approximately 150-350 MBq. Measurement data was compared to Monte Carlo simulations using the egs_chamber user code in EGSnrc 2019.Main results. Agreement withink= 1 uncertainty between measured and MC predictedDwwas observed for all dosimeters, except the A20-375 ion chamber during the second131I experiment. Despite the agreement, the measured values were generally lower than predicted values by 5%-15%. The uncertainties atk = 1 remain large (5%-30% depending on the dosimeter) relative to other forms of radiation therapy.Significance. Despite high uncertainties, the overall agreement between measured and simulated absorbed doses is promising for the use of dosimeter-based RPT measurements in the validation of MC predictedDw.
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Affiliation(s)
| | | | - Benjamin Palmer
- University of Wisconsin-Madison, WI, United States of America
| | | | - Tyler Bradshaw
- University of Wisconsin-Madison, WI, United States of America
| | - A Hans Vija
- Siemens Healthineers, United States of America
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Godson HF, Manickam R, Ponmalar YR, Ganesh KM, Saminathan S, Chandraraj V, Kumar AS, George S, Raman A, Singh RR. Effect of Detector Orientation and Influence of Jaw Position in the Determination of Small-field Output Factor with Various Detectors for High-energy Photon Beams. J Med Phys 2024; 49:73-83. [PMID: 38828075 PMCID: PMC11141751 DOI: 10.4103/jmp.jmp_148_23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2023] [Revised: 02/13/2024] [Accepted: 02/13/2024] [Indexed: 06/05/2024] Open
Abstract
Background Accurate dose measurements are difficult in small fields due to charge particle disequilibrium, partial source occlusion, steep dose gradient, and the finite size of the detector. Aim The study aims to determine the output factor using various detectors oriented in parallel and perpendicular orientations for three different tertiary collimating systems using 15 MV photon beams. In addition, this study analyzes how the output factor could be affected by different configurations of X and Y jaws above the tertiary collimators. Materials and Methods Small field output factor measurements were carried out with three detectors for different tertiary collimating systems such as BrainLab stereotactic cones, BrainLab mMLC and Millennium MLC namely. To analyze the effect of jaw position on output factor, measurements have been carried out by positioning the jaws at the edge, 0.25, 0.5, and 1.0 cm away from the tertiary collimated field. Results The data acquired with 15 MV photon beams show significant differences in output factor obtained with different detectors for all collimating systems. For smaller fields when compared to microDiamond, the SRS diode underestimates the output by up to -1.7% ± 0.8% and -2.1% ± 0.3%, and the pinpoint ion chamber underestimates the output by up to -8.1% ± 1.4% and -11.9% ± 1.9% in their parallel and perpendicular orientation respectively. A large increase in output factor was observed in the small field when the jaw was moved 0.25 cm symmetrically away from the tertiary collimated field. Conclusion The investigated data on the effect of jaw position inferred that the position of the X and Y jaw highly influences the output factors of the small field. It also confirms that the output factor highly depends on the configuration of X and Y jaw settings, the tertiary collimating system as well as the orientation of the detectors in small fields.
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Affiliation(s)
- Henry Finlay Godson
- Department of Radiation Oncology, Christian Medical College, Vellore, Tamil Nadu, India
| | - Ravikumar Manickam
- Department of Radiotherapy, Sri Shankara Cancer Hospital and Research Centre, Bengaluru, Karnataka, India
| | - Y. Retna Ponmalar
- Department of Radiation Oncology, Christian Medical College, Vellore, Tamil Nadu, India
| | - K. M. Ganesh
- Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka, India
| | - Sathiyan Saminathan
- Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka, India
| | - Varatharaj Chandraraj
- Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka, India
| | - A. Sathish Kumar
- Department of Radiation Oncology, Christian Medical College, Vellore, Tamil Nadu, India
| | - Seby George
- Department of Radiation Oncology, Christian Medical College, Vellore, Tamil Nadu, India
| | - Arun Raman
- Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka, India
| | - Rabi Raja Singh
- Department of Radiation Oncology, Christian Medical College, Vellore, Tamil Nadu, India
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Schofield A, Newall M, Inwood D, Downes S, Corde S. Commissioning of Aktina SRS cones and dosimetric validation of the RayStation photon Monte Carlo dose calculation algorithm. Phys Eng Sci Med 2023; 46:1503-1518. [PMID: 37603132 DOI: 10.1007/s13246-023-01315-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2022] [Accepted: 07/27/2023] [Indexed: 08/22/2023]
Abstract
Clinical implementation of SRS cones demands particular experimental care and dosimetric considerations in order to deliver precise and safe radiotherapy to patients. The purpose of this work was to present the commissioning data of recent Aktina cones combined with a 6MV flattened beam produced by an Elekta VersaHD linear accelerator. Additionally, the modelling process, and an assessment of dosimetric accuracy of the RayStation Monte Carlo dose calculation algorithm for cone based SRS was performed. There are currently no studies presenting beam data for this equipment and none that outlines the modelling parameters and validation of dose calculation using RayStation's photon Monte Carlo dose engine with cones. Beam data was measured using an SFD and a microDiamond and benchmarked against EBT3 film for cones of diameter 5-39 mm. Modelling was completed and validated within homogeneous and heterogeneous phantoms. End-to-end image-guided validation was performed using a StereoPHAN™ housing, an SRS MapCHECK and EBT3 film, and calculation time was investigated as a function of statistical uncertainty and field diameter. The TPS calculations agreed with measured data within their estimated uncertainties and clinical treatment plans could be calculated in under a minute. The data presented serves as a reference for others commissioning Aktina stereotactic cones and the modelling parameters serve similarly, while providing a starting point for those commissioning the same TPS algorithm for use with cones. It has been shown in this work that RayStation's Monte Carlo photon dose algorithm performs satisfactorily in the presence of SRS cones.
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Affiliation(s)
- Andy Schofield
- Radiation Oncology Department, Prince of Wales Hospital, Randwick, NSW, 2031, Australia
| | - Matthew Newall
- Radiation Oncology Department, Prince of Wales Hospital, Randwick, NSW, 2031, Australia
| | - Dean Inwood
- Radiation Oncology Department, Prince of Wales Hospital, Randwick, NSW, 2031, Australia
| | - Simon Downes
- Radiation Oncology Department, Prince of Wales Hospital, Randwick, NSW, 2031, Australia
| | - Stéphanie Corde
- Radiation Oncology Department, Prince of Wales Hospital, Randwick, NSW, 2031, Australia.
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia.
- Illawara Health and Medical Research Institute, University of Wollongong, Wollongong, NSW, 2522, Australia.
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Ketabi A, Karbasi S, Faghihi R, Mosleh-Shirazi MA. A phantom-based experimental and Monte Carlo study of the suitability of in-vivo diodes and TLD for entrance in-vivo dosimetry in small-to-medium sized 6 MV photon fields. Radiat Phys Chem Oxf Engl 1993 2022. [DOI: 10.1016/j.radphyschem.2022.110411] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Hartmann GH, Andreo P, Kapsch RP, Zink K. Cema-based formalism for the determination of absorbed dose for high-energy photon beams. Med Phys 2021; 48:7461-7475. [PMID: 34613620 DOI: 10.1002/mp.15266] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2021] [Revised: 07/26/2021] [Accepted: 09/23/2021] [Indexed: 11/08/2022] Open
Abstract
PURPOSE Determination of absorbed dose is well established in many dosimetry protocols and considered to be highly reliable using ionization chambers under reference conditions. If dosimetry is performed under other conditions or using other detectors, however, open questions still remain. Such questions frequently refer to appropriate correction factors. A converted energy per mass (cema)-based approach to formulate such correction factors offers a good understanding of the specific response of a detector for dosimetry under various measuring conditions and thus an estimate of pros and cons of its application. METHODS Determination of absorbed dose requires the knowledge of the beam quality correction factor kQ,Qo , where Q denotes the quality of a user beam and Qo is the quality of the radiation used for calibration. In modern Monte Carlo (MC)-based methods, kQ,Qo is directly derived from the MC-calculated dose conversion factor, which is the ratio between the absorbed dose at a point of interest in water and the mean absorbed dose in the sensitive volume of an ion chamber. In this work, absorbed dose is approximated by the fundamental quantity cema. This approximation allows the dose conversion factor to be substituted by the cema conversion factor. Subsequently, this factor is decomposed into a product of cema ratios. They are identified as the stopping power ratio water to the material in the sensitive detector volume, and as the correction factor for the fluence perturbation of the secondary charged particles in the detector cavity caused by the presence of the detector. This correction factor is further decomposed with respect to the perturbation caused by the detector cavity and that caused by external detector properties. The cema-based formalism was subsequently tested by MC calculations of the spectral fluence of the secondary charged particles (electrons and positrons) under various conditions. RESULTS MC calculations demonstrate that considerable fluence perturbation may occur particularly under non-reference conditions. Cema-based correction factors to be applied in a 6-MV beam were obtained for a number of ionization chambers and for three solid-state detectors. Feasibility was shown at field sizes of 4 × 4 and 0.5 cm × 0.5 cm. Values of the cema ratios resulting from the decomposition of the dose conversion factor can be well correlated with detector response. Under the small field conditions, the internal fluence correction factor of ionization chambers is considerably dependent on volume averaging and thus on the shape and size of the cavity volume. CONCLUSIONS The cema approach is particularly useful at non-reference conditions including when solid-state detectors are used. Perturbation correction factors can be expressed and evaluated by cema ratios in a comprehensive manner. The cema approach can serve to understand the specific response of a detector for dosimetry to be dependent on (a) radiation quality, (b) detector properties, and (c) electron fluence changes caused by the detector. This understanding may also help to decide which detector is best suited for a specific measurement situation.
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Affiliation(s)
- Günther H Hartmann
- Division of Medical Physics in Radiation Oncology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Pedro Andreo
- Department of Medical Radiation Physics and Nuclear Medicine, Karolinska University Hospital, Stockholm, Sweden.,Department of Oncology-Pathology, Karolinska Institutet, Stockholm, Sweden
| | | | - Klemens Zink
- Institut fuer Medizinische Physik und Strahlenschutz (IMPS), University of Applied Sciences, Giessen, Giessen, Germany.,Department for Radiotherapy and Radiooncology, University Medical Center Giessen-Marburg, Marburg, Germany.,Marburg Iontherapy Center (MIT), Marburg, Germany
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6
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Das IJ, Francescon P, Moran JM, Ahnesjö A, Aspradakis MM, Cheng CW, Ding GX, Fenwick JD, Saiful Huq M, Oldham M, Reft CS, Sauer OA. Report of AAPM Task Group 155: Megavoltage photon beam dosimetry in small fields and non-equilibrium conditions. Med Phys 2021; 48:e886-e921. [PMID: 34101836 DOI: 10.1002/mp.15030] [Citation(s) in RCA: 56] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2021] [Revised: 05/06/2021] [Accepted: 06/02/2021] [Indexed: 12/14/2022] Open
Abstract
Small-field dosimetry used in advance treatment technologies poses challenges due to loss of lateral charged particle equilibrium (LCPE), occlusion of the primary photon source, and the limited choice of suitable radiation detectors. These challenges greatly influence dosimetric accuracy. Many high-profile radiation incidents have demonstrated a poor understanding of appropriate methodology for small-field dosimetry. These incidents are a cause for concern because the use of small fields in various specialized radiation treatment techniques continues to grow rapidly. Reference and relative dosimetry in small and composite fields are the subject of the International Atomic Energy Agency (IAEA) dosimetry code of practice that has been published as TRS-483 and an AAPM summary publication (IAEA TRS 483; Dosimetry of small static fields used in external beam radiotherapy: An IAEA/AAPM International Code of Practice for reference and relative dose determination, Technical Report Series No. 483; Palmans et al., Med Phys 45(11):e1123, 2018). The charge of AAPM task group 155 (TG-155) is to summarize current knowledge on small-field dosimetry and to provide recommendations of best practices for relative dose determination in small megavoltage photon beams. An overview of the issue of LCPE and the changes in photon beam perturbations with decreasing field size is provided. Recommendations are included on appropriate detector systems and measurement methodologies. Existing published data on dosimetric parameters in small photon fields (e.g., percentage depth dose, tissue phantom ratio/tissue maximum ratio, off-axis ratios, and field output factors) together with the necessary perturbation corrections for various detectors are reviewed. A discussion on errors and an uncertainty analysis in measurements is provided. The design of beam models in treatment planning systems to simulate small fields necessitates special attention on the influence of the primary beam source and collimating devices in the computation of energy fluence and dose. The general requirements for fluence and dose calculation engines suitable for modeling dose in small fields are reviewed. Implementations in commercial treatment planning systems vary widely, and the aims of this report are to provide insight for the medical physicist and guidance to developers of beams models for radiotherapy treatment planning systems.
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Affiliation(s)
- Indra J Das
- Department of Radiation Oncology, Northwestern Memorial Hospital, Northwestern University Feinberg School of Medicine, Chicago, IL, USA
| | - Paolo Francescon
- Department of Radiation Oncology, Ospedale Di Vicenza, Vicenza, Italy
| | - Jean M Moran
- Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, NY, USA
| | - Anders Ahnesjö
- Medical Radiation Sciences, Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden
| | - Maria M Aspradakis
- Institute of Radiation Oncology, Cantonal Hospital of Graubünden, Chur, Switzerland
| | - Chee-Wai Cheng
- Department of Radiation Oncology, University Hospitals Cleveland Medical Center, Cleveland, OH, USA
| | - George X Ding
- Department of Radiation Oncology, Vanderbilt University School of Medicine, Nashville, TN, USA
| | - John D Fenwick
- Molecular and Clinical Cancer Medicine, Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool, UK
| | - M Saiful Huq
- Department of Radiation Oncology, University of Pittsburgh, School of Medicine and UPMC Hillman Cancer Center, Pittsburgh, PA, USA
| | - Mark Oldham
- Department of Radiation Oncology, Duke University Medical Center, Durham, NC, USA
| | - Chester S Reft
- Department of Radiation Oncology, University of Chicago, Chicago, IL, USA
| | - Otto A Sauer
- Department of Radiation Oncology, Klinik fur Strahlentherapie, University of Würzburg, Würzburg, Germany
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Dwivedi S, Kansal S, Dangwal VK, Bharati A, Shukla J. Dosimetry of a 6 MV flattening filter-free small photon beam using various detectors. Biomed Phys Eng Express 2021; 7. [PMID: 33930875 DOI: 10.1088/2057-1976/abfd80] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2021] [Accepted: 04/30/2021] [Indexed: 11/12/2022]
Abstract
The present study aimed to dosimetrically evaluate the small-fields of a 6 MV flattening filter-free (FFF) photon beam using different detectors.The 6 MV FFF photon beam was used for measurement of output factor, depth dose, and beam profile of small-fields of sizes 0.6 cm × 0.6 cm to 6.0 cm × 6.0 cm. The five detectors used were SNC125c, PinPoint, EDGE, EBT3, and TLD-100. All measurements were performed as per the International Atomic Energy Agency TRS 483 protocol. Output factors measured using different detectors as direct reading ratios showed significant variation for the smallest fields, whereas after correcting them according to TRS 483, all sets of output factors were nearly compatible with each other when measurement uncertainty was also considered. The beam profile measured using SNC125c showed the largest penumbra for all field sizes, whereas the smallest was recorded with EDGE. Compared with that of EBT3, the surface dose was found to be much higher for all the other detectors. PinPoint, EBT3, TLD-100, and EDGE were found to be the detector of choice for small-field output factor measurements; however, PinPoint needs special attention when used for the smallest field size (0.6 cm × 0.6 cm). EDGE and EBT3 are optimal for measuring beam profiles. EBT3, PinPoint, and EDGE can be selected for depth dose measurements, and EBT3 is suitable for surface dose estimation.
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Affiliation(s)
- Shekhar Dwivedi
- Department of Medical Physics, Tata Memorial Centre, Homi Bhabha Cancer Hospital and Research Centre, Mullanpur, Mohali, Punjab, 140901, India.,Department of Physics, Maharaja Ranjit Singh Punjab Technical University, Bathinda, Punjab, 151001, India
| | - Sandeep Kansal
- Department of Physics, Maharaja Ranjit Singh Punjab Technical University, Bathinda, Punjab, 151001, India
| | - Vinod Kumar Dangwal
- Department of Radiotherapy, Government Medical College, Patiala, Punjab, 147001, India
| | - Avinav Bharati
- Department of Radiation Oncology, Dr Ram Manohar Lohia Institute of Medical Sciences, Lucknow, Uttar Pradesh, 226010, India
| | - Jooli Shukla
- Department of Physics, Dr Bhimrao Ambedkar University, Agra, Uttar Pradesh, 282004, India
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8
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Charles PH, Crowe SB, Kairn T. Technical Note: Small field dose correction factors for radiochromic film in lung phantoms. Med Phys 2021; 48:2667-2672. [PMID: 33619729 DOI: 10.1002/mp.14799] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Revised: 02/02/2021] [Accepted: 02/16/2021] [Indexed: 12/20/2022] Open
Abstract
PURPOSE Radiochromic film has been established as a detector that can be used without the need for perturbation correction factors for small field dosimetry in water. However, perturbation factors in low density media such as lung have yet to be published. This study calculated the factors required to account for the perturbation of radiochromic film when used for small field dosimetry in lung equivalent material. METHOD Monte Carlo simulations were used to calculate dose to Gafchromic EBT3 film when placed inside a lung phantom. The beam simulated had a nominal energy of 6 MV and the field sizes simulated ranged from 10 × 10 mm2 to 30 × 30 mm2 . The lung density simulated was varied between 0.2 and 0.3 g/cm3 . Each simulation was repeated with the film replaced by lung material (the same as the surrounding medium), and the required correction factors for film dosimetry in lung ( D M e d , Q D D e t , Q ) were calculated by dividing the dose in lung by the dose in film. RESULTS For field sizes 30 × 30 mm2 and larger, no correction factors were required. At a 20 × 20 mm2 field size, small corrections were required, but were within the approximate accuracy of film dosimetry (~2%). For a 10 × 10 mm2 field size, significant correction factors need to be applied (0.935 for lung density of 0.20 g/cm3 to 0.963 for lung density of 0.30 g/cm3 ). The values lower than one mean that the film is over-responding. At the "upstream" lung-water interface the correction factors were close to unity; while at the downstream interface the corrections required were marginally smaller to those at the center of lung. One centimeter or more away from the interfaces, the correction factor did not vary as a function distance from the interface (in the beam direction). Away from the central axis (perpendicular to the beam direction), the correction factors increased slightly (away from unity) as a function of off-axis distance, before abruptly changing direction at the penumbra, with the film actually under-responding by ~10% outside the field edges. CONCLUSION Accurate dosimetry of very small fields (15 × 15 mm2 or smaller) using radiochromic film requires correction factors for the perturbation of the film on the surrounding lung material. This correction factor was as high as 6.5% for a 10 × 10 mm2 field size and a density of 0.2 g/cm3 . This will increase if either the density or the field size decrease further. This correction factor does not vary as a function of depth in lung once charged particle equilibrium is established.
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Affiliation(s)
- Paul H Charles
- Herston Biofabrication Institute, Metro North Hospital and Health Service, Herston, Queensland, 4029, Australia.,School of Information Technology and Electrical Engineering, University of Queensland, St Lucia, Queensland, 4072, Australia.,School of Chemistry and Physics, Queensland University of Technology, Brisbane, Queensland, 4000, Australia
| | - Scott B Crowe
- Herston Biofabrication Institute, Metro North Hospital and Health Service, Herston, Queensland, 4029, Australia.,School of Information Technology and Electrical Engineering, University of Queensland, St Lucia, Queensland, 4072, Australia.,School of Chemistry and Physics, Queensland University of Technology, Brisbane, Queensland, 4000, Australia.,Cancer Care Services, Royal Brisbane & Women's Hospital, Herston, Queensland, 4029, Australia
| | - Tanya Kairn
- Herston Biofabrication Institute, Metro North Hospital and Health Service, Herston, Queensland, 4029, Australia.,School of Information Technology and Electrical Engineering, University of Queensland, St Lucia, Queensland, 4072, Australia.,School of Chemistry and Physics, Queensland University of Technology, Brisbane, Queensland, 4000, Australia.,Cancer Care Services, Royal Brisbane & Women's Hospital, Herston, Queensland, 4029, Australia
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9
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Bouchard H. Reference dosimetry of modulated and dynamic photon beams. Phys Med Biol 2021; 65:24TR05. [PMID: 33438582 DOI: 10.1088/1361-6560/abc3fb] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
In the late 1980s, a new technique was proposed that would revolutionize radiotherapy. Now referred to as intensity-modulated radiotherapy, it is at the core of state-of-the-art photon beam delivery techniques, such as helical tomotherapy and volumetric modulated arc therapy. Despite over two decades of clinical application, there are still no established guidelines on the calibration of dynamic modulated photon beams. In 2008, the IAEA-AAPM work group on nonstandard photon beam dosimetry published a formalism to support the development of a new generation of protocols applicable to nonstandard beam reference dosimetry (Alfonso et al 2008 Med. Phys. 35 5179-86). The recent IAEA Code of Practice TRS-483 was published as a result of this initiative and addresses exclusively small static beams. But the plan-class specific reference calibration route proposed by Alfonso et al (2008 Med. Phys. 35 5179-86) is a change of paradigm that is yet to be implemented in radiotherapy clinics. The main goals of this paper are to provide a literature review on the dosimetry of nonstandard photon beams, including dynamic deliveries, and to discuss anticipated benefits and challenges in a future implementation of the IAEA-AAPM formalism on dynamic photon beams.
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Affiliation(s)
- Hugo Bouchard
- Département de physique, Université de Montréal, Complexe des sciences, 1375 Avenue Thérèse-Lavoie-Roux, Montréal, Québec H2V 0B3, Canada. Centre de recherche du Centre hospitalier de l'Université de Montréal, 900 Rue Saint-Denis, Montréal, Québec H2X 0A9, Canada. Département de radio-oncologie, Centre hospitalier de l'Université de Montréal (CHUM), 1051 Rue Sanguinet, Montréal, Québec H2X 3E4, Canada
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Lam S, Bradley D, Khandaker M. Small-field radiotherapy photon beam output evaluation: Detectors reviewed. Radiat Phys Chem Oxf Engl 1993 2021. [DOI: 10.1016/j.radphyschem.2020.108950] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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11
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Lam SE, Noor NM, Bradley DA, Mahmud R, Pawanchek M, Abdul Rashid HA. Small-field output ratio determination using 6 mol% Ge-doped silica fibre dosimeters. Biomed Phys Eng Express 2020; 6. [PMID: 35042836 DOI: 10.1088/2057-1976/abc2a4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2020] [Accepted: 10/19/2020] [Indexed: 11/12/2022]
Abstract
This work investigates the suitability of locally fabricated 6 mol% Ge-doped optical fibres as dosimeters for small-field output ratio measurements. Two fabrications of fibre, cylindrical (CF) and flat (FF) fibres, were used to measure doses in small photon fields, from 4 to 15 mm. The findings were compared to those of commercial Ge-doped fibre (COMM), EBT3 film and an IBA CC01 ionization chamber. Irradiations were carried out using a 6 MV SRS photon beam operating at a dose rate of 1000 cGy min-1, delivering a dose of 16 Gy. To minimise the possibility of the fibres failing to be exposed to the intended dose in small fields, the fibres were accommodated in a custom-made Perspex phantom. For the 4 mm cone the CF and FF measured output ratios were found to be smaller than obtained with EBT3 film by 32% and 13% respectively. Conversely, while for the 6 to 15 mm cone fields the FF output ratios were consistently greater than those obtained using EBT3 film, the CF output ratios differed from those of EBT3 film by at most 3.2%, at 6 mm, otherwise essentially agreeing with EBT3 values at the other field sizes. For the 4 to 7.5 mm cones, all output ratios obtained from Ge-doped optical fibre measurements were greater than those of IBA CC01 ionization chamber. The measured FF and CF output ratios for the 7.5 to 15 mm cones agreed with published MC estimates to within 15% and 13%, respectively. Down to 6 mm cone field, present measurements point to the potential of CF as a small-field dosimeter, its use recommended to be complemented by the use of EBT3 film for small-field dosimetry.
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Affiliation(s)
- S E Lam
- Centre for Biomedical Physics, School of Healthcare and Medical Sciences, Sunway University, 47500 Petaling Jaya, Selangor, Malaysia.,Department of Radiology, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia
| | - N Mohd Noor
- Department of Radiology, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia.,Department of Radiology, Teaching Hospital Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia
| | - D A Bradley
- Centre for Biomedical Physics, School of Healthcare and Medical Sciences, Sunway University, 47500 Petaling Jaya, Selangor, Malaysia.,Department of Physics, University of Surrey, Guildford, Surrey GU2 7XH, United Kingdom
| | - R Mahmud
- Department of Radiology, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia.,Centre for Diagnostic Nuclear Imaging, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia
| | - M Pawanchek
- Department of Radiotherapy and Oncology, National Cancer Institute, 62250 W.P. Putrajaya, Malaysia
| | - H A Abdul Rashid
- Faculty of Engineering, Multimedia University, 63100 Cyberjaya, Selangor, Malaysia
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13
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Lechner W, Primeßnig A, Nenoff L, Wesolowska P, Izewska J, Georg D. The influence of errors in small field dosimetry on the dosimetric accuracy of treatment plans. Acta Oncol 2020; 59:511-517. [PMID: 31694438 DOI: 10.1080/0284186x.2019.1685127] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Background: Dosimetric effects of inaccuracies of output factors (OFs) implemented in treatment planning systems (TPSs) were investigated.Materials and methods: Modified beam models (MBM) for which the OFs of small fields (down to 1 × 1 cm2) were increased by up to 12% compared to the original beam models (OBM) were created for two TPSs. These beam models were used to recalculate treatment plans of different complexity. Treatment plans using stereotactic 3D-conformal (s3D-CRT) for brain metastasis as well as VMAT plans for head and neck and prostate cancer patients were generated. Dose distributions calculated with the MBM and the OBM were compared to measured dose distributions acquired using film dosimetry and a 2D-detector-array. For the s3D-CRT plans the calculated and measured dose at the isocenter was evaluated. For VMAT, gamma pass rates (GPRs) were calculated using global gamma index with 3%/3 mm, 2%/3 mm, 1%/3 mm and 2%/2 mm with a 20% threshold. Contribution of small fields to the total fluence was expressed as the ratio (F) of fluence trough leaf openings smaller than 2 cm to the total fluence.Results: Using film dosimetry for the s3D-CRT plans, the average of the ratio of calculated dose to measured dose at the isocenter was 1.01 and 1.06 for the OBM and MBM model, respectively. A significantly lower GPR of the MBM compared to the OBM was only found for the localized prostate cases (F = 12.4%) measured with the 2D-detector-array and an acceptance criterion of 1%/3 mm.Conclusion: The effects of uncertainties in small field OFs implemented in TPSs are most pronounced for s3D-CRT cases and can be clearly identified using patient specific quality assurance. For VMAT these effects mainly remain undetected using standard patient specific quality assurance. Using tighter acceptance criteria combined with an analysis of the fluence generated by small fields can help identifying inaccuracies of OFs implemented in TPSs.
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Affiliation(s)
- Wolfgang Lechner
- Department of Radiation Oncology, Division Medical Physics, Medical University Vienna, Vienna, Austria
- Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Medical University of Vienna, Vienna, Austria
| | - Alexander Primeßnig
- Department of Radiation Oncology, Division Medical Physics, Medical University Vienna, Vienna, Austria
- Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Medical University of Vienna, Vienna, Austria
| | - Lena Nenoff
- Department of Radiation Oncology, Division Medical Physics, Medical University Vienna, Vienna, Austria
- Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Medical University of Vienna, Vienna, Austria
| | - Paulina Wesolowska
- International Atomic Energy Agency, Vienna International Centre, Vienna, Austria
| | - Joanna Izewska
- International Atomic Energy Agency, Vienna International Centre, Vienna, Austria
| | - Dietmar Georg
- Department of Radiation Oncology, Division Medical Physics, Medical University Vienna, Vienna, Austria
- Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Medical University of Vienna, Vienna, Austria
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Track and dose-average LET dependence of Gafchromic EBT3 and MD-V3 films exposed to low-energy photons. Sci Rep 2020; 10:2361. [PMID: 32047227 PMCID: PMC7012855 DOI: 10.1038/s41598-020-59233-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2019] [Accepted: 01/28/2020] [Indexed: 11/25/2022] Open
Abstract
Gafchromic films are widely used in radiotherapy using photons, electrons and protons. Dosimetric characteristics of the films in terms of beam-quality is of great importance for a better evaluation of the absorbed-dose in the clinic. In proton-therapy, film’s response has been reported in terms of track-average, LΔ,T, or dose-average, LΔ,D, linear energy transfer (LET), concluding that LΔ,D is a more reliable parameter than LΔ,T. Nonetheless, in photon-beams, the film’s response is generally scrutinised in terms of photon-energy. This work aimed at investigating, the total (TEF) and secondary (SE) electron fluence produced in EBT3 and MD-V3 films exposed to 20 kV-160 kV x-ray and 60Co beams and their corresponding LΔ,T and LΔ,D to determine their influence on the film’s relative-efficiency, REFilm. Regardless the film-model, at energies below 100 keV, LΔ,D for TEF are about 1.7 to 2.5 times those of LΔ,T while for SE they are relatively similar (8–29%). For 60Co-gamma, LΔ,D for TEF and SE are approximately 9 and 4 times LΔ,T, respectively, which implies that LΔ,D is more important for high-photon energies. Independent of the electron-fluence and film-model, REFilm is almost constant at low average-LET, rapidly increases and thereafter steadily rises with average-LET. The REFilm−LET curve indicated that LΔ,D is more sensitive to small change than LΔ,T and if it is evaluated for SE, it would even be more appropriate to better describing the dosimeter response induced by photons in terms of ionization-density instead of LΔ,T for TEF, as generally done. Based on these results, once can conclude that the effect of the average-LET on the film’s response should be considered when use for clinical-dosimetry using photons and not only the energy.
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Lechner W, Georg D, Palmans H. An analytical formalism for the assessment of dose uncertainties due to positioning uncertainties. Med Phys 2020; 47:1357-1363. [PMID: 31880323 PMCID: PMC7078844 DOI: 10.1002/mp.13991] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2019] [Revised: 12/18/2019] [Accepted: 12/18/2019] [Indexed: 11/12/2022] Open
Abstract
PURPOSE To present an analytical formalism for the in depth assessment of uncertainties of field output factors in small fields related to detector positioning based on dose profile measurements. Additionally, a procedure for the propagation of these uncertainties was developed. METHODS Based on the assumption that one dimensional and two dimensional second-order polynomial functions can be fitted to dose profiles of small photon beams, equations for the calculation of the expectation value, the variance, and the standard deviation were developed. The following fitting procedures of the dose profiles were considered: A one-dimensional case (1D), a quasi two-dimensional case (2Dq) based on independently measured line profiles and a full 2D case (2Df) which also considers cross-correlations in a two-dimensional dose distribution. A rectangular and a Gaussian probability density function (PDF) characterizing the probability of possible positions of the detector relative to the maximum dose were used. Uncertainty components such as the finite resolution of the scanning water phantom, the reproducibility of the determination of the position of the maximum dose, and the reproducibility of the collimator system were investigated. This formalism was tested in a 0.5 x 0.5 cm2 photon field where dose profiles were measured using a radiochromic film, a synthetic diamond detector, and an unshielded diode detector. Additionally, the dose distribution measured with the radiochromic film was convoluted with a convolution kernel mimicking the active volume of the unshielded diode. RESULTS Analytic expressions for the calculation of uncertainties on field output factors were found for the 1D, the 2Dq, and the 2Df case. The uncertainty of the field output factor related to the relative position of the detector to the maximum dose increased quadratically with increasing limits of possible detector positions. Analysis of the radiochromic film showed that the 2Dq case gave a more conservative assessment of the uncertainty compared to the 2Df case with a difference of < 0.1%. The 2Dq case applied to the film measurements agreed well with the same approach as was applied to the unshielded diode. The investigated uncertainty components propagated to an uncertainty of the field output factors of 0.5% and 0.4% for the synthetic diamond and the unshielded diode, respectively. Additionally, the expectation value was lower than the maximum dose. The difference was 0.4% and 0.3% for the synthetic diamond and the unshielded diode, respectively. CONCLUSIONS The assessment of uncertainties of field output factors related to detector positioning is feasible using the proposed formalism. The 2Dq case is applicable when using online detectors. Accurate positioning in small fields is essential for accurate dosimetry as its related uncertainty increases quadratically. The observed drop of the expectation value needs to be considered in small field dosimetry.
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Affiliation(s)
- Wolfgang Lechner
- Division of Medical Physics, Department of Radiation Oncology, Medical University Vienna, 1090, Vienna, Austria
| | - Dietmar Georg
- Division of Medical Physics, Department of Radiation Oncology, Medical University Vienna, 1090, Vienna, Austria
| | - Hugo Palmans
- EBG MedAustron GmbH, Marie-Curie Straße 5, 2700, Wiener Neustadt, Austria.,National Physical Laboratory, Teddington, TW, 11 0LW, UK
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Irmen P, Reft C, Fitzherbert C, Solin L, Hand C. Verification of representative data for output factors of SRS cones utilizing IAEA TRS 483 recommendations. ACTA ACUST UNITED AC 2019; 64:215011. [DOI: 10.1088/1361-6560/ab47dd] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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Evaluating small field dosimetry with the Acuros XB (AXB) and analytical anisotropic algorithm (AAA) dose calculation algorithms in the eclipse treatment planning system. JOURNAL OF RADIOTHERAPY IN PRACTICE 2019. [DOI: 10.1017/s1460396919000104] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
AbstractBackground:An increasing number of external beam treatment modalities including intensity modulated radiation therapy, volumetric modulated arc therapy (VMAT) and stereotactic radiosurgery uses very small fields for treatment planning and delivery. However, there are major challenges in small photon field dosimetry, due to the partial occlusion of the direct photon beam source’s view from the measurement point, lack of lateral charged particle equilibrium, steep dose-rate gradient and volume averaging effect of the detector response and variation of the energy fluence in the lateral direction of the beam. Therefore, experimental measurements of dosimetric parameters such as percent depth doses (PDDs), beam profiles and relative output factors (ROFs) for small fields continue to be a challenge.Materials and Methods:In this study, we used a homogeneous water phantom and the heterogeneous anthropomorphic stereotactic end-to-end verification (STEEV) head phantom for all dose measurements and calculations. PDDs, lateral dose profiles and ROFs were calculated in the Eclipse Treatment Planning System version 13·6 using the Acuros XB (AXB) and the analytical anisotropic algorithms (AAAs) in a homogenous water phantom. Monte Carlo (MC) simulations and measurements using the Exradin W1 Scintillator were also accomplished for four photon energies: 6 MV, 6FFF, 10 MV and 10FFF. Two VMAT treatment plans were generated for two different targets: one located in the brain and the other in the neck (close to the trachea) in the head phantom (CIRS, Norfolk, VA, USA). A Varian Truebeam linear accelerator (Varian, Palo Alto, CA, USA) was used for all treatment deliveries. Calculated results with AXB and AAA were compared with MC simulations and measurements.Results:The average difference of PDDs between W1 Exradin Scintillator measurements and MC simulations, AAA and AXB algorithm calculations were 1·2, 2·4 and 3·2%, respectively, for all field sizes and energies. AXB and AAA showed differences in ROF of about 0·3 and 2·9%, respectively, compared with W1 Exradin Scintillator measured values. For the target located in the brain in the head phantom, the average dose difference between W1 Exradin Scintillator and the MC simulations, AAA and AXB were 0·2, 3·2 and 2·7%, respectively, for all field sizes. Similarly, for the target located in the neck, the respective dose differences were 3·8, 5·7 and 3·5%.Conclusion:In this study, we compared dosimetric parameters such as PDD, beam profile and ROFs in water phantom and isocenter point dose measurements in an anthropomorphic head phantom representing a patient. We observed that measurements using the W1 Exradin scintillator agreed well with MC simulations and can be used efficiently for dosimetric parameters such as PDDs and dose profiles and patient-specific quality assurance measurements for small fields. In both homogenous and heterogeneous media, the AXB algorithm dose prediction agrees well with MC and measurements and was found to be superior to the AAA algorithm.
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Monasor Denia P, Castellet García MDC, Manjón García C, Quirós Higueras JD, de Marco Blancas N, Bonaque Alandí J, Juan Senabre XJ, Santos Serra A, López-Tarjuelo J. Comparison of detector performance in small 6 MV and 6 MV FFF beams using a Versa HD accelerator. PLoS One 2019; 14:e0213253. [PMID: 30856183 PMCID: PMC6411166 DOI: 10.1371/journal.pone.0213253] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2018] [Accepted: 02/18/2019] [Indexed: 11/18/2022] Open
Abstract
1. BACKGROUND & PURPOSE Investigate the applicability of a series of detectors in small field dosimetry and the possible differences between their responses to FF and FFF beams. This work extends upon the series of detectors used by other authors to also include metal-oxide-semiconductor field-effect transistors (MOSFETs) detectors and radiochromic film. We also included a later correction of output factors (OFs) recommended by the recently published IAEA´s code of practice TRS 483 on dosimetry of small static fields used in external beam radiotherapy. 2. MATERIALS & METHODS The OFs, profiles, and PDDs of 6 MV and 6 MV FFF beams were measured with 11 different detectors using field sizes between 0.6 × 0.6 cm2 and 10 × 10 cm2. 3. RESULTS The OFs of the FFF beams were lower than those of the FF beams for field sizes larger than 3 × 3 cm2 but higher for field sizes smaller than 3 × 3 cm2. After applying the IAEA´s TRS 483 corrections, the final OFs were compatible with our initial results when considering uncertainties involved. Small-volume detectors are preferable for measuring the penumbra of these small fields where this attribute is higher in the crossline direction than in the inline direction. The R100 of equivalent-quality FFF beams was higher compared to the corresponding flattened beams. 4. CONCLUSIONS We observed no difference for the dose responses between 6 MV and 6 MV FFF beams for any of the detectors. OF results, profiles and PDDs were clearly consistent with the previously published literature regarding the Versa HD linac. Correcting our first OFs, taken as ratio of detector charges, with the IAEA´s TRS 483 corrections to obtain the final OFs, did not make the former significantly different.
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Affiliation(s)
- Paula Monasor Denia
- Servicio de Radiofísica y Protección Radiológica, Consorcio Hospitalario Provincial de Castellón, Castellón de la Plana, España
| | | | - Carla Manjón García
- Servicio de Radiofísica y Protección Radiológica, Consorcio Hospitalario Provincial de Castellón, Castellón de la Plana, España
| | - Juan David Quirós Higueras
- Servicio de Radiofísica y Protección Radiológica, Consorcio Hospitalario Provincial de Castellón, Castellón de la Plana, España
| | - Noelia de Marco Blancas
- Servicio de Radiofísica y Protección Radiológica, Consorcio Hospitalario Provincial de Castellón, Castellón de la Plana, España
| | - Jorge Bonaque Alandí
- Servicio de Radiofísica y Protección Radiológica, Consorcio Hospitalario Provincial de Castellón, Castellón de la Plana, España
| | - Xavier Jordi Juan Senabre
- Servicio de Radiofísica y Protección Radiológica, Consorcio Hospitalario Provincial de Castellón, Castellón de la Plana, España
| | - Agustín Santos Serra
- Servicio de Radiofísica y Protección Radiológica, Consorcio Hospitalario Provincial de Castellón, Castellón de la Plana, España
| | - Juan López-Tarjuelo
- Servicio de Radiofísica y Protección Radiológica, Consorcio Hospitalario Provincial de Castellón, Castellón de la Plana, España
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Wegener S, Weick S, Sauer OA. Influence of a transverse magnetic field on the response of different detectors in a high energy photon beam near the surface. Z Med Phys 2019; 29:22-30. [DOI: 10.1016/j.zemedi.2018.07.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2017] [Revised: 05/29/2018] [Accepted: 07/02/2018] [Indexed: 10/28/2022]
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Casar B, Gershkevitsh E, Mendez I, Jurković S, Huq MS. A novel method for the determination of field output factors and output correction factors for small static fields for six diodes and a microdiamond detector in megavoltage photon beams. Med Phys 2018; 46:944-963. [PMID: 30521073 PMCID: PMC7379629 DOI: 10.1002/mp.13318] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2018] [Revised: 11/21/2018] [Accepted: 11/21/2018] [Indexed: 12/04/2022] Open
Abstract
Purpose The goal of this work is to provide a large and consistent set of data for detector‐specific output correction factors, kQclin,Qreffclin,fref, for small static fields for seven solid‐state detectors and to determine field output factors, ΩQclin,Qreffclin,fref, using EBT3 radiochromic films and W1 plastic scintillator as reference detectors on two different linear accelerators and four megavoltage photon beams. Consistent measurement conditions and recommendations given in the International Code of Practice TRS‐483 for small‐field dosimetry were followed throughout the study. Methods ΩQclin,Qreffclin,fref were determined on two linacs, Elekta Versa HD and Varian TrueBeam, for 6 and 10 MV beams with and without flattening filter and for nine fields ranging from 0.5 × 0.5 cm2 to 10 × 10 cm2. Signal readings obtained with EBT3 radiochromic films and W1 plastic scintillator were fitted by an analytical function. Volume averaging correction factors, determined from two‐dimensional (2D) dose matrices obtained with EBT3 films and fitted to bivariate Gaussian function, were used to correct measured signals. kQclin,Qreffclin,fref were determined empirically for six diodes, IBA SFD, IBA Razor, PTW 60008 P, PTW 60012 E, PTW 60018 SRS, and SN EDGE, and a PTW 60019 microDiamond detector. Results Field output factors and detector‐specific kQclin,Qreffclin,fref are presented in the form of analytical functions as well as in the form of discrete values. It is found that in general, for a given linac, small‐field output factors need to be determined for every combination of beam energy and filtration (WFF or FFF) and field size as the differences between them can be statistically significant (P < 0.05). For different beam energies, the present data for kQclin,Qreffclin,fref are found to differ significantly (P < 0.05) from the corresponding data published in TRS‐483 mostly for the smallest fields (<1.5 cm). For the PTW microDiamond detector, statistically significant differences (P < 0.05) between kQclin,Qreffclin,fref values were found for all investigated beams on an Elekta Versa HD linac for field sizes 0.5 × 0.5 cm2 and 0.8 × 0.8 cm2. Significant differences in kQclin,Qreffclin,fref between beams of a given energy but with and without flattening filters are found for measurements made in small fields (<1.5 cm) at a given linac. Differences in kQclin,Qreffclin,fref are also found when measurements are made at different linacs using the same beam energy filtration combination; for the PTW microDiamond detector, these differences were found to be around 6% and were considered as significant. Conclusions Selection of two reference detectors, EBT3 films and W1 plastic scintillator, and use of an analytical function, is a novel approach for the determination of ΩQclin,Qreffclin,fref for small static fields in megavoltage photon beams. Large set of kQclin,Qreffclin,fref data for seven solid‐state detectors and four beam energies determined on two linacs by a single group of researchers can be considered a valuable supplement to the literature and the TRS‐483 dataset.
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Affiliation(s)
- Božidar Casar
- Department for Dosimetry and Quality of Radiological Procedures, Institute of Oncology Ljubljana, Zaloška 2, 1000, Ljubljana, Slovenia
| | - Eduard Gershkevitsh
- Medical Physics Service, North Estonia Medical Centre, J. Sütiste tee 19, 13419, Tallinn, Estonia
| | - Ignasi Mendez
- Department for Dosimetry and Quality of Radiological Procedures, Institute of Oncology Ljubljana, Zaloška 2, 1000, Ljubljana, Slovenia
| | - Slaven Jurković
- Medical Physics Department, University Hospital Rijeka, Krešimirova 42, 51000, Rijeka, Croatia
| | - M Saiful Huq
- Department of Radiation Oncology, University of Pittsburgh School of Medicine and UPMC Hillman Cancer Center, Pittsburgh, PA, USA
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Johnstone CD, Therriault-Proulx F, Beaulieu L, Bazalova-Carter M. Characterization of a plastic scintillating detector for the Small Animal Radiation Research Platform (SARRP). Med Phys 2018; 46:394-404. [PMID: 30417377 DOI: 10.1002/mp.13283] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2018] [Revised: 10/07/2018] [Accepted: 10/30/2018] [Indexed: 11/09/2022] Open
Abstract
PURPOSE The purpose of this study was to characterize a small plastic scintillator developed for high resolution, real-time dosimetry of therapy and imaging x-ray beams delivered by an image-guided small animal irradiator. MATERIALS AND METHODS A 1 mm diameter, 1 mm long polystyrene BCF-60 scintillating fiber dosimeter was characterized with 220 kVp therapy and 40, 50, 60, 70, and 80 kVp imaging beams on the Small Animal Research Platform (SARRP). Scintillator output, sensitivity (charge per unit dose), linearity, and 0.2-mm resolution beam profile measurements were performed. A validated in-house Monte Carlo (MC) model of the SARRP was used to compute detailed energy spectra at locations of dosimetry, and validated scintillator measurement with MC simulations. Mass energy-absorption coefficients from the National Institute of Standards and Technology (NIST) tables convolved with MC-derived spectra were used in conjunction with Birks ionization quenching factors to correct scintillator output. An air kerma calibration method was employed to correct scintillator output for in-air beam profile measurements with open, 5 × 5, and 3 × 3 mm2 square field sizes, and compared to MC simulations. RESULTS Scintillator dose response showed excellent linearity (R2 ≥ 0.999) for all sensitivity measurements, including output as a function of tube current. Detector sensitivity was 2.41 μC Gy-1 for the 220 kVp therapy beam, and it ranged from 1.21 to 1.32 μC Gy-1 for the 40-80 imaging beams. Percentage difference in sensitivity between the therapy and imaging beams before sensitivity correction and after using the Birks quenching factors were 52.3% and 10.2%, respectively. Percentage differences between the therapy and imaging beam sensitivities after using the air kerma calibration method for in-air measurements was excellent and below 0.3%. In-air beam profile measurements agreed to MC simulations within a mean difference of 2.4% for the 5 × 5 and 3 × 3 mm2 field sizes, however, the scintillator showed signs of volume averaging at the penumbra edges. CONCLUSIONS A small plastic scintillator was characterized for therapy and imaging energies of a small animal irradiator, with output corrected for using an in-house MC model of the irradiator. The characterization of the scintillator detector system for small fields presents steps toward implementing real-time measurements for quality assurance and small animal treatment and imaging dose verification.
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Affiliation(s)
| | - François Therriault-Proulx
- Departement de Radio-Oncologie and Centre de recherche du CHU de Quebec, CHU de Quebec, Quebec, QC, G1R 3S1, Canada
| | - Luc Beaulieu
- Departement de Radio-Oncologie and Centre de recherche du CHU de Quebec, CHU de Quebec, Quebec, QC, G1R 3S1, Canada.,Departement de physique and Centre de recherche sur le Cancer, Université Laval, Quebec, QC, G1V 0A6, Canada
| | - Magdalena Bazalova-Carter
- Department of Physics and Astronomy, University of Victoria, Victoria, British Columbia, V8P 5C2, Canada
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Palmans H, Andreo P, Huq MS, Seuntjens J, Christaki KE, Meghzifene A. Dosimetry of small static fields used in external photon beam radiotherapy: Summary of TRS‐483, the IAEA–AAPM international Code of Practice for reference and relative dose determination. Med Phys 2018; 45:e1123-e1145. [DOI: 10.1002/mp.13208] [Citation(s) in RCA: 123] [Impact Index Per Article: 20.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2017] [Revised: 07/24/2018] [Accepted: 07/30/2018] [Indexed: 12/18/2022] Open
Affiliation(s)
- Hugo Palmans
- Medical Radiation Science National Physical Laboratory Teddington TW11 0LWUK
- Department of Medical Physics EBG MedAustron GmbH A‐2700Wiener Neustadt Austria
| | - Pedro Andreo
- Department of Medical Physics and Nuclear Medicine Karolinska University Hospital SE‐17176Stockholm Sweden
| | - M. Saiful Huq
- Department of Radiation Oncology University of Pittsburgh School of Medicine and UPMC Hillman Cancer Center Pittsburgh PA15232USA
| | - Jan Seuntjens
- Medical Physics Unit McGill University Montréal QCH3A 0G4Canada
| | - Karen E. Christaki
- Dosimetry and Medical Radiation Physics Section International Atomic Energy Agency A‐1400Vienna Austria
| | - Ahmed Meghzifene
- Dosimetry and Medical Radiation Physics Section International Atomic Energy Agency A‐1400Vienna Austria
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Alhakeem E, Zavgorodni S. Output and ($k_{{{Q}_{{\rm clin},}}{{Q}_{{\rm msr}}}}^{{{\,f}_{{\rm clin},}}{{f}_{{\rm msr}}}}$ ) correction factors measured and calculated in very small circular fields for microDiamond and EFD-3G detectors. ACTA ACUST UNITED AC 2018; 63:155002. [DOI: 10.1088/1361-6560/aacfb2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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Prado A, Lozano FR, Cabello E, Díaz R, Rot MJ. Dosimetric characterization of a 5 mm diameter BrainLab cone for radiosurgery. Biomed Phys Eng Express 2018. [DOI: 10.1088/2057-1976/aace50] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Shukaili KA, Corde S, Petasecca M, Pereveratylo V, Lerch M, Jackson M, Rosenfeld A. "Characterization of ELEKTA SRS cone collimator using high spatial resolution monolithic silicon detector array". J Appl Clin Med Phys 2018; 19:114-124. [PMID: 29790261 PMCID: PMC6036391 DOI: 10.1002/acm2.12345] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2017] [Revised: 04/03/2018] [Accepted: 04/07/2018] [Indexed: 11/05/2022] Open
Abstract
PURPOSE To investigate the accuracy of the dosimetry of radiation fields produced by small ELEKTA cone collimators used for stereotactic radiosurgery treatments (SRS) using commercially available detectors EBT3 GafchromicTM film, IBA Stereotactic diode (SFD), and the recently developed detector DUO, which is a monolithic silicon orthogonal linear diode array detector. METHODS These three detectors were used for the measurement of beam profiles, output factors, and percentage depth dose for SRS cone collimators with cone sizes ranging from 5 to 50 mm diameter. The measurements were performed at 10 cm depth and 90 cm SSD. RESULTS The SRS cone beam profiles measured with DUO, EBT3 film, and IBA SFD agreed well, results being in agreement within ±0.5 mm in the FWHM, and ±0.7 mm in the penumbra region. The output factor measured by DUO with 0.5 mm air gap above agrees within ±1% with EBT3. The OF measured by IBA SFD (corrected for the over-response) agreed with both EBT3 and DUO within ±2%. All three detectors agree within ±2% for PDD measurements for all SRS cones. CONCLUSIONS The characteristics of the ELEKTA SRS cone collimator have been evaluated by using a monolithic silicon high spatial resolution detector DUO, EBT3, and IBA SFD diode. The DUO detector is suitable for fast real-time quality assurance dosimetry in small radiation fields typical for SRS/SRT. This has been demonstrated by its good agreement of measured doses with EBT 3 films.
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Affiliation(s)
- Khalsa Al Shukaili
- Centre for Medical Radiation PhysicsUniversity of WollongongWollongongNSWAustralia
- National Oncology CentreRoyal HospitalMuscatOman
| | - Stéphanie Corde
- Centre for Medical Radiation PhysicsUniversity of WollongongWollongongNSWAustralia
- Illawarra Health and Medical Research InstituteWollongongNSWAustralia
- Nelune Comprehensive Cancer CentrePrince of Wales HospitalRandwickNSWAustralia
| | - Marco Petasecca
- Centre for Medical Radiation PhysicsUniversity of WollongongWollongongNSWAustralia
- Illawarra Health and Medical Research InstituteWollongongNSWAustralia
| | | | - Michael Lerch
- Centre for Medical Radiation PhysicsUniversity of WollongongWollongongNSWAustralia
- Illawarra Health and Medical Research InstituteWollongongNSWAustralia
| | - Michael Jackson
- Centre for Medical Radiation PhysicsUniversity of WollongongWollongongNSWAustralia
- Nelune Comprehensive Cancer CentrePrince of Wales HospitalRandwickNSWAustralia
| | - Anatoly Rosenfeld
- Centre for Medical Radiation PhysicsUniversity of WollongongWollongongNSWAustralia
- Illawarra Health and Medical Research InstituteWollongongNSWAustralia
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Andreo P. The physics of small megavoltage photon beam dosimetry. Radiother Oncol 2018; 126:205-213. [DOI: 10.1016/j.radonc.2017.11.001] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2017] [Revised: 10/16/2017] [Accepted: 11/01/2017] [Indexed: 10/18/2022]
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27
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Oliver CP, Butler DJ, Takau V, Williams I. Survey of 5 mm small-field output factor measurements in Australia. J Appl Clin Med Phys 2018; 19:329-337. [PMID: 29368796 PMCID: PMC5849830 DOI: 10.1002/acm2.12259] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2017] [Revised: 12/07/2017] [Accepted: 12/08/2017] [Indexed: 11/25/2022] Open
Abstract
The Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) held a comparison exercise in April 2016 where participants came to ARPANSA and measured the output factor of a nominal 5 mm cone attached to the ARPANSA Elekta Synergy (Elekta, Crawley, UK) linear accelerator. The goal of the exercise was to compare the consistency and methods used by independent medical physicists in measuring small‐field output factors. ARPANSA provided a three‐dimensional scanning tank for detector setup and positioning, but the participants were required to measure the output factor with their own detectors. No information regarding output factors previously measured was supplied to participants to make each result as independent as possible. Fifteen groups travelled to ARPANSA bringing a wide range of detectors and methods. A total of 30 measurements of the output factor were made. The standard deviation of the measurements (excluding one expected outlier from an uncorrected ionization chamber measurement) was 3.6%. The results provide an insight into the consistency of small‐field dosimetry being performed in Australia and New Zealand at the present time.
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Affiliation(s)
- Christopher P Oliver
- Australian Radiation Protection and Nuclear Safety Agency, Yallambie, Vic, Australia
| | - Duncan J Butler
- Australian Radiation Protection and Nuclear Safety Agency, Yallambie, Vic, Australia
| | - Viliami Takau
- Australian Radiation Protection and Nuclear Safety Agency, Yallambie, Vic, Australia
| | - Ivan Williams
- Australian Radiation Protection and Nuclear Safety Agency, Yallambie, Vic, Australia
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28
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Lechner W, Wesolowska P, Azangwe G, Arib M, Alves VGL, Suming L, Ekendahl D, Bulski W, Samper JLA, Vinatha SP, Siri S, Tomsej M, Tenhunen M, Povall J, Kry SF, Followill DS, Thwaites DI, Georg D, Izewska J. A multinational audit of small field output factors calculated by treatment planning systems used in radiotherapy. Phys Imaging Radiat Oncol 2018; 5:58-63. [PMID: 33458370 PMCID: PMC7807586 DOI: 10.1016/j.phro.2018.02.005] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2017] [Revised: 02/14/2018] [Accepted: 02/15/2018] [Indexed: 11/03/2022] Open
Abstract
BACKGROUND AND PURPOSE An audit methodology for verifying the implementation of output factors (OFs) of small fields in treatment planning systems (TPSs) used in radiotherapy was developed and tested through a multinational research group and performed on a national level in five different countries. MATERIALS AND METHODS Centres participating in this study were asked to provide OFs calculated by their TPSs for 10 × 10 cm2, 6 × 6 cm2, 4 × 4 cm2, 3 × 3 cm2 and 2 × 2 cm2 field sizes using an SSD of 100 cm. The ratio of these calculated OFs to reference OFs was analysed. The action limit was ±3% for the 2 × 2 cm2 field and ±2% for all other fields. RESULTS OFs for more than 200 different beams were collected in total. On average, the OFs for small fields calculated by TPSs were generally larger than measured reference data. These deviations increased with decreasing field size. On a national level, 30% and 31% of the calculated OFs of the 2 × 2 cm2 field exceeded the action limit of 3% for nominal beam energies of 6 MV and for nominal beam energies higher than 6 MV, respectively. CONCLUSION Modern TPS beam models generally overestimate the OFs for small fields. The verification of calculated small field OFs is a vital step and should be included when commissioning a TPS. The methodology outlined in this study can be used to identify potential discrepancies in clinical beam models.
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Affiliation(s)
- Wolfgang Lechner
- International Atomic Energy Agency, Vienna, Austria
- Medical University of Vienna, Department of Radiation Oncology, Vienna, Austria
- Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Vienna, Austria
| | | | - Godfrey Azangwe
- International Atomic Energy Agency, Vienna, Austria
- National University of Science and Technology, Bulawayo, Zimbabwe
| | - Mehenna Arib
- Centre De Recherche Nucleaire D’alger, Alger Gare, Algeria
| | | | - Luo Suming
- Chinese Centre for Disease Control and Prevention, Beijing, China
| | | | - Wojciech Bulski
- Maria Sklodowska-Curie Memorial Cancer Centre and Institute of Oncology, Warsaw, Poland
| | | | - Sumanth Panyam Vinatha
- Radiation Standards Section, Radiation Safety Systems Division, Bhabha Atomic Research Centre Trombay, Mumbai, India
| | - Srimanoroth Siri
- SSDL, Bureau of Radiation and Medical Devices, Department of Medical Science, Nonthaburi, Thailand
| | - Milan Tomsej
- CHU Charleroi, Hopital Andre Vesale, Montigny-le-Tilleul, Belgium
| | - Mikko Tenhunen
- Helsinki University Hospital, Cancer Centre, Helsinki, Finland
| | - Julie Povall
- Department of Medical Physics & Engineering, St James’s University Hospital, Leeds, United Kingdom
| | - Stephen F. Kry
- Imaging and Radiation Oncology Core Houston QA Centre, MD Anderson Cancer Centre, Houston, TX, United States
| | - David S. Followill
- Imaging and Radiation Oncology Core Houston QA Centre, MD Anderson Cancer Centre, Houston, TX, United States
| | - David I. Thwaites
- University of Leeds, St James’s University Hospital, Leeds, United Kingdom
- Institute of Medical Physics, School of Physics, University of Sydney, Sydney, Australia
| | - Dietmar Georg
- Medical University of Vienna, Department of Radiation Oncology, Vienna, Austria
- Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Vienna, Austria
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Christiansen E, Muir B, Belec J, Vandervoort E. Small composite field correction factors for the CyberKnife radiosurgery system: clinical and PCSR plans. Phys Med Biol 2017; 62:9240-9259. [PMID: 29058682 DOI: 10.1088/1361-6560/aa954c] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
A formalism has been proposed for small and non-standard photon fields in which [Formula: see text] correction factors are used to correct dosimeter response in small fields (indiviual or composite) relative to that in a larger machine-specific reference (MSR) field. For clinical plans consisting of several fields, a plan-class specific reference (PCSR) plan can also be defined, serving as an intermediate calibration field between the MSR and clinical plans within a certain plan-class. In this work, the formalism was applied in the calculation of [Formula: see text] for 21 clinical plans delivered by the [Formula: see text] radiosurgery system, each plan employing one or two of the smallest diameter collimators: 5 mm, 7.5 mm, and 10 mm. Three detectors were considered: the Exradin A16 and A26 micro chambers, and the W1 plastic scintillator. The clinical plans were grouped into 7 plan-classes according to commonly shared characteristics. The suitability of using a PCSR plan to represent the detector response of each plan within the plan-class was investigated. Total and intermediate correction factors were calculated using the [Formula: see text] Monte Carlo user code. The corrections for the micro chambers were large, primarily due to the presence of the low-density air cavity and the volume averaging effect. The correction for the scintillator was found to be close to unity for most plans, indicating that this detector may be used to measure small clinical plan correction factors in any plan except for those using the 5 mm collimator. The PCSR plan was shown to be applicable to plan-classes comprising isocentric plans only, with plan-classes divided according to collimator size. For non-isocentric plans, the variation of [Formula: see text] as a function of the point of measurement within a single plan, as well as the high inter-plan-class variability of the correction factor, precludes the use of a PCSR plan.
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Kulmala A, Tenhunen M. Ionization chamber radial response deconvolution in megavoltage photon beam. Phys Med Biol 2017; 62:7505-7519. [PMID: 28486216 DOI: 10.1088/1361-6560/aa71f7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The aim of this paper is to study a radial response model as a method, to correct output factor results gathered with ionization chambers of different size and shape in cone collimated RT fields. An enhanced version of a non-parametric super-resolution deconvolution method able to model a radial response function of a small cylinder symmetric ionization chamber is described and demonstrated. The radial response of four ionization chambers with different geometry and radius are estimated using 6 MV photon beam in water at the isocentre plane. Finally the validity of the estimates is tested by applying the response functions to the output factor measurements of 4-20 mm conical collimators. The enhanced method is demonstrated by obtaining the response function characteristics with a spatial uncertainty smaller than 0.1 mm when the distance from chamber axis is larger than 0.5 mm. In all studied ionization chambers, a significant local response maximum is found close to the air cavity boundary. The agreement between the output factor results of different chambers is promising, the largest difference (max-min) in output factor is 4% obtained for the smallest 4 mm cone size.
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Affiliation(s)
- A Kulmala
- Helsinki University Hospital, Cancer Center, PO Box 180, 00029 Helsinki, Finland. Doctoral programme in Materials Research and Nanosciences (MATRENA), University of Helsinki, Finland
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31
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Jennings MW, Rutten TP, Ottaway DJ. Evaluation of the signal quality of an inexpensive CMOS camera towards imaging a high-resolution plastic scintillation detector array. RADIAT MEAS 2017. [DOI: 10.1016/j.radmeas.2017.07.004] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Dosimetric characterization of small fields using a plastic scintillator detector: A large multicenter study. Phys Med 2017; 41:33-38. [DOI: 10.1016/j.ejmp.2017.03.024] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/17/2017] [Revised: 03/23/2017] [Accepted: 03/28/2017] [Indexed: 12/31/2022] Open
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Poppinga D, Delfs B, Meyners J, Harder D, Poppe B, Looe HK. The output factor correction as function of the photon beam field size - direct measurement and calculation from the lateral dose response functions of gas-filled and solid detectors. Z Med Phys 2017; 28:224-235. [PMID: 28869164 DOI: 10.1016/j.zemedi.2017.07.006] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2017] [Revised: 07/07/2017] [Accepted: 07/17/2017] [Indexed: 10/19/2022]
Abstract
The first aim of this study has been to extend the systematic experimental study of the field size dependence of the output factor correction for three micro-ionization chambers (PTW 31014, PTW 31022 and IBA Razor chamber), two silicon diodes (PTW 60017 and IBA Razor Diode) and the synthetic diamond detector microDiamond (PTW 60019) in a 6 MV photon beam down to an effective field side length of 2.6mm, and to summarize the present knowledge of this factor by treating it as a function of the dosimetric field size. In order to vary the dosimetric field size over this large range, output factors measurements were performed at source-to-surface distances of 60cm and 90cm. Since the output factors obtained with the organic scintillation detector Exradin W1 (Standard Imaging, Middleton, USA) at all field sizes closely agreed with those measured by EBT3 radiochromic films (ISP Corp, Wayne, USA), the scintillation detector served as the reference detector. The measured output correction factors reflect the influences of the volume averaging and density effects upon the uncorrected output factor values. In case of the microDiamond detector these opposing influences result in output factor correction values less than 1 for moderately small field sizes and larger than 1 for very small field sizes. Our results agree with most of the published experimental as well as Monte-Carlo simulated data within detector-specific limits of uncertainty. The dosimetric field side length has been identified as a reliable determinant of the output factor correction, and typical functional curve shapes of the field-size dependent output factor correction vs. dosimetric field side length have been associated with gas-filled, silicon diode and synthetic diamond detectors. The second aim of this study has been a novel, semi-empirical approach to calculate the field-size dependent output correction factors of small photon detectors by convolving film measured true dose profile data with measured lateral response functions of the detectors. To achieve this, the set of previously published 2D lateral dose response functions was complemented by those of the novel detectors PTW PinPoint chamber 31022 (PTW Freiburg, Freiburg, Germany), Razor chamber and Razor Diode (IBA Dosimetry, Schwarzenbruck, Germany). The output correction factors calculated from the lateral dose response functions closely fit with the directly measured output correction factors, thus supporting the latter by an independent method.
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Affiliation(s)
- Daniela Poppinga
- University Clinic for Medical Radiation Physics, Medical Campus Pius-Hospital, Carl von Ossietzky University, Georgstraße 12, 26121 Oldenburg, Germany.
| | - Björn Delfs
- University Clinic for Medical Radiation Physics, Medical Campus Pius-Hospital, Carl von Ossietzky University, Georgstraße 12, 26121 Oldenburg, Germany
| | - Jutta Meyners
- Radiotherapy Department, Imland Hospital, Lilienstraße 20-28, 24768 Rendsburg, Germany
| | - Dietrich Harder
- Prof. em., Medical Physics and Biophysics, Georg August University, Wilhelmsplatz 1, 37073 Göttingen, Germany
| | - Björn Poppe
- University Clinic for Medical Radiation Physics, Medical Campus Pius-Hospital, Carl von Ossietzky University, Georgstraße 12, 26121 Oldenburg, Germany
| | - Hui Khee Looe
- University Clinic for Medical Radiation Physics, Medical Campus Pius-Hospital, Carl von Ossietzky University, Georgstraße 12, 26121 Oldenburg, Germany
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34
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Sharma DS, Chaudhary RK, Sharma SD, Pilakkal S, Rasal SK, Sawant MB, Phurailatpam RD. Experimental determination of stereotactic cone size and detector specific output correction factor. Br J Radiol 2017. [DOI: 10.1259/bjr.20160918] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Affiliation(s)
- Dayananda Shamurailatpam Sharma
- Department of Radiation Oncology, Kokilaben Dhirubhai Ambani Hospital and Medical Research Institute, Andheri West, Mumbai, Maharashtra, India
| | | | | | - Shaju Pilakkal
- Department of Radiation Oncology, Kokilaben Dhirubhai Ambani Hospital and Medical Research Institute, Andheri West, Mumbai, Maharashtra, India
| | - Sachin K Rasal
- Department of Radiation Oncology, Kokilaben Dhirubhai Ambani Hospital and Medical Research Institute, Andheri West, Mumbai, Maharashtra, India
| | - Mayur B Sawant
- Department of Radiation Oncology, Kokilaben Dhirubhai Ambani Hospital and Medical Research Institute, Andheri West, Mumbai, Maharashtra, India
| | - Reena D Phurailatpam
- Department of Radiation Oncology, Advance Centre for Treatment, Research and Education in Cancer, Navi Mumbai, India
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35
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Reggiori G, Stravato A, Pimpinella M, Lobefalo F, De Coste V, Fogliata A, Mancosu P, De Rose F, Palumbo V, Scorsetti M, Tomatis S. Use of PTW-microDiamond for relative dosimetry of unflattened photon beams. Phys Med 2017; 38:45-53. [PMID: 28610696 DOI: 10.1016/j.ejmp.2017.05.046] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/05/2016] [Revised: 01/31/2017] [Accepted: 05/03/2017] [Indexed: 10/19/2022] Open
Abstract
PURPOSE The increasing interest in SBRT treatments encourages the use of flattening filter free (FFF) beams. Aim of this work was to evaluate the performance of the PTW60019 microDiamond detector under 6MV and 10MVFFF beams delivered with the EDGE accelerator (Varian Medical System, Palo Alto, USA). A flattened 6MV beam was also considered for comparison. METHODS Short term stability, dose linearity and dose rate dependence were evaluated. Dose per pulse dependence was investigated in the range 0.2-2.2mGy/pulse. MicroDiamond profiles and output factors (OFs) were compared to those obtained with other detectors for field sizes ranging from 40×40cm2 to 0.6×0.6cm2. In small fields, volume averaging effects were evaluated and the relevant correction factors were applied for each detector. RESULTS MicroDiamond short term stability, dose linearity and dependence on monitor unit rate were less than 0.8% for all energies. Response variations with dose per pulse were found within 1.8%. MicroDiamond output factors (OF) values differed from those measured with the reference ion-chamber for less than 1% up to 40×40cm2 fields where silicon diodes overestimate the dose of ≈3%. For small fields (<3×3cm2) microDiamond and the unshielded silicon diode were in good agreement. CONCLUSIONS MicroDiamond showed optimal characteristics for relative dosimetry even under high dose rate beams. The effects due to dose per pulse dependence up to 2.2mGy/pulse are negligible. Compared to other detectors, microDiamond provides accurate OF measurements in the whole range of field sizes. For fields <1cm correction factors accounting for fluence perturbation and volume averaging could be required.
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Affiliation(s)
- Giacomo Reggiori
- Physics Service of Radiation Oncology Dept., Humanitas Clinical and Research Hospital, Milan-Rozzano, Italy.
| | - Antonella Stravato
- Physics Service of Radiation Oncology Dept., Humanitas Clinical and Research Hospital, Milan-Rozzano, Italy
| | - Maria Pimpinella
- Istituto Nazionale di Metrologia delle Radiazioni Ionizzanti, ENEA-INMRI C R Casaccia, Roma, Italy
| | - Francesca Lobefalo
- Physics Service of Radiation Oncology Dept., Humanitas Clinical and Research Hospital, Milan-Rozzano, Italy
| | - Vanessa De Coste
- Istituto Nazionale di Metrologia delle Radiazioni Ionizzanti, ENEA-INMRI C R Casaccia, Roma, Italy
| | - Antonella Fogliata
- Physics Service of Radiation Oncology Dept., Humanitas Clinical and Research Hospital, Milan-Rozzano, Italy
| | - Pietro Mancosu
- Physics Service of Radiation Oncology Dept., Humanitas Clinical and Research Hospital, Milan-Rozzano, Italy
| | - Fiorenza De Rose
- Radiotherapy and Radiosurgery Department, Humanitas Clinical and Research Hospital, Milan-Rozzano, Italy
| | - Valentina Palumbo
- Physics Service of Radiation Oncology Dept., Humanitas Clinical and Research Hospital, Milan-Rozzano, Italy
| | - Marta Scorsetti
- Radiotherapy and Radiosurgery Department, Humanitas Clinical and Research Hospital, Milan-Rozzano, Italy; Department of Biomedical Sciences, Humanitas University, Rozzano, Milano, Italy
| | - Stefano Tomatis
- Physics Service of Radiation Oncology Dept., Humanitas Clinical and Research Hospital, Milan-Rozzano, Italy
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36
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Puxeu-Vaqué J, Duch MA, Nailon WH, Cruz Lizuain M, Ginjaume M. Field correction factors for a PTW-31016 Pinpoint ionization chamber for both flattened and unflattened beams. Study of the main sources of uncertainties. Med Phys 2017; 44:1930-1938. [DOI: 10.1002/mp.12189] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2016] [Revised: 02/20/2017] [Accepted: 02/23/2017] [Indexed: 11/07/2022] Open
Affiliation(s)
- Josep Puxeu-Vaqué
- Servei de Física Mèdica i Protecció radiològica; Institut Català d'Oncologia (ICO); L'Hospitalet de Llobregat; Barcelona Spain
- Department of Oncology Physics; Edinburgh Cancer Centre; Western General Hospital; Edinburgh Scotland
| | - Maria A. Duch
- Institut de Tècniques Energètiques (INTE); Universitat Politècnica de Catalunya; Barcelona Spain
| | - William H. Nailon
- Department of Oncology Physics; Edinburgh Cancer Centre; Western General Hospital; Edinburgh Scotland
| | - M. Cruz Lizuain
- Servei de Física Mèdica i Protecció radiològica; Institut Català d'Oncologia (ICO); L'Hospitalet de Llobregat; Barcelona Spain
| | - Mercè Ginjaume
- Institut de Tècniques Energètiques (INTE); Universitat Politècnica de Catalunya; Barcelona Spain
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Yarahmadi M, Wegener S, Sauer OA. Energy and field size dependence of a silicon diode designed for small-field dosimetry. Med Phys 2017; 44:1958-1964. [DOI: 10.1002/mp.12195] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2016] [Revised: 02/17/2017] [Accepted: 02/28/2017] [Indexed: 11/10/2022] Open
Affiliation(s)
- Mehran Yarahmadi
- Department of Medical Physics; Faculty of Medicine; Kurdistan University of Medical Sciences; Sanandaj Iran
| | - Sonja Wegener
- Department of Radiation Oncology; University of Würzburg; Josef-Schneider-Strasse 11 97080 Würzburg Germany
| | - Otto A. Sauer
- Department of Radiation Oncology; University of Würzburg; Josef-Schneider-Strasse 11 97080 Würzburg Germany
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Marinelli M, Prestopino G, Verona C, Verona-Rinati G. Experimental determination of the PTW 60019 microDiamond dosimeter active area and volume. Med Phys 2017; 43:5205. [PMID: 27587052 DOI: 10.1118/1.4961402] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE Small field output correction factors have been studied by several research groups for the PTW 60019 microDiamond (MD) dosimeter, by comparing the response of such a device with both reference dosimeters and Monte Carlo simulations. A general good agreement is observed for field sizes down to about 1 cm. However, evident inconsistencies can be noticed when comparing some experimental results and Monte Carlo simulations obtained for smaller irradiation fields. This issue was tentatively attributed by some authors to unintentional large variations of the MD active surface area. The aim of the present study is a nondestructive experimental determination of the MD active surface area and active volume. METHODS Ten MD dosimeters, one MD prototype, and three synthetic diamond samples were investigated in the present work. 2D maps of the MD response were recorded under scanned soft x-ray microbeam irradiation, leading to an experimental determination of the device active surface area. Profiles of the device responses were measured as well. In order to evaluate the MD active volume, the thickness of the diamond sensing layer was independently evaluated by capacitance measurements and alpha particle detection experiments. The MD sensitivity, measured at the PTW calibration laboratory, was also used to calculate the device active volume thickness. RESULTS An average active surface area diameter of (2.19 ± 0.02) mm was evaluated by 2D maps and response profiles of all the MDs. Average active volume thicknesses of (1.01 ± 0.13) μm and (0.97 ± 0.14) μm were derived by capacitance and sensitivity measurements, respectively. The obtained results are well in agreement with the nominal values reported in the manufacturer dosimeter specifications. A homogeneous response was observed over the whole device active area. Besides the one from the device active volume, no contributions from other components of the housing nor from encapsulation materials were observed in the 2D response maps. CONCLUSIONS The obtained results demonstrate the high reproducibility of the MD fabrication process. The observed discrepancies among the output correction factors reported by several authors for MD response in very small fields are very unlikely to be ascribed to unintentional variations of the device active surface area and volume. It is the opinion of the authors that the role of the volume averaging as well as of other perturbation effects should be separately investigated instead, both experimentally and by Monte Carlo simulations, in order to better clarify the behaviour of the MD response in very small fields.
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Affiliation(s)
- Marco Marinelli
- INFN-Dipartimento di Ingegneria Industriale, Università di Roma "Tor Vergata," Via del Politecnico 1, Roma 00133, Italy
| | - G Prestopino
- INFN-Dipartimento di Ingegneria Industriale, Università di Roma "Tor Vergata," Via del Politecnico 1, Roma 00133, Italy
| | - C Verona
- INFN-Dipartimento di Ingegneria Industriale, Università di Roma "Tor Vergata," Via del Politecnico 1, Roma 00133, Italy
| | - G Verona-Rinati
- INFN-Dipartimento di Ingegneria Industriale, Università di Roma "Tor Vergata," Via del Politecnico 1, Roma 00133, Italy
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Wegener S, Sauer OA. Separation of scatter from small MV beams and its effect on detector response. Med Phys 2017; 44:1139-1148. [PMID: 28063164 DOI: 10.1002/mp.12091] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2016] [Revised: 12/20/2016] [Accepted: 01/01/2017] [Indexed: 11/09/2022] Open
Abstract
PURPOSE Separating the scatter from the primary component of a MV beam to study detector response separately in each case for a better understanding of the role of different effects influencing the response in nonstandard fields. METHODS Detector response in three different experimental setups was investigated for a variety of different types (diamond, shielded and unshielded diodes, ionization chamber and film): (a). Detectors positioned in water under a thin steel pole blocking the central part of the beam, yielding only the response to the scatter part of the beam. (b). Detectors positioned in air under a PMMA cap to approximate the contribution of the primary beam without scatter. (c). Detectors positioned in water in the standard open field configuration to obtain a superposition of both. RESULTS Detector differences became more clearly observable when the primary beam was blocked and detector behavior heavily depended on the construction type. It was possible to calculate the response in the open fields from the values measured in the blocked configuration with 1% accuracy for all studied field sizes between 0.8 and 10 cm and for all detectors. CONCLUSIONS The limitations of clinically used detectors in nonstandard situations were illustrated in the extreme situation of just scattered radiation reaching the detector. By experimentally separating scatter from the primary beam, the roles of different effects on the detector response were observed.
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Affiliation(s)
- Sonja Wegener
- Department of Radiation Oncology, University of Würzburg, 97080, Würzburg, Germany
| | - Otto A Sauer
- Department of Radiation Oncology, University of Würzburg, 97080, Würzburg, Germany
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40
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Papaconstadopoulos P, Archambault L, Seuntjens J. Experimental investigation on the accuracy of plastic scintillators and of the spectrum discrimination method in small photon fields. Med Phys 2017; 44:654-664. [DOI: 10.1002/mp.12064] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2016] [Revised: 09/23/2016] [Accepted: 12/05/2016] [Indexed: 11/05/2022] Open
Affiliation(s)
- Pavlos Papaconstadopoulos
- McGill University; Medical Physics Unit, Department of Radiation Oncology, SMBD Jewish General Hospital; 3755 Côte-Ste-Catherine Road Montréal, Québec H3T 1E2 Canada
| | - Louis Archambault
- Département de Physique, de Génie Physique et d’ Optique; Université Laval; Quèbec G1K 7P4 Canada
- Département de Radio-Oncologie; Hotel-Dieu de Québec, Centre Hospitalier Universitaire de Quèbec; Quèbec G1R 2J6 Canada
| | - Jan Seuntjens
- McGill University; Medical Physics Unit, Cedars Cancer Centre; 1001 Décarie Montréal, Québec H4A 3J1 Canada
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Shukaili KA, Petasecca M, Newall M, Espinoza A, Perevertaylo VL, Corde S, Lerch M, Rosenfeld AB. A 2D silicon detector array for quality assurance in small field dosimetry: DUO. Med Phys 2017; 44:628-636. [DOI: 10.1002/mp.12060] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2016] [Revised: 09/21/2016] [Accepted: 11/27/2016] [Indexed: 12/31/2022] Open
Affiliation(s)
- Khalsa Al Shukaili
- Centre for Medical Radiation Physics; University of Wollongong; Wollongong NSW 2522 Australia
- National Oncology Centre; Royal Hospital; Muscat Oman
| | - Marco Petasecca
- Centre for Medical Radiation Physics; University of Wollongong; Wollongong NSW 2522 Australia
| | - Matthew Newall
- Centre for Medical Radiation Physics; University of Wollongong; Wollongong NSW 2522 Australia
| | - Anthony Espinoza
- Centre for Medical Radiation Physics; University of Wollongong; Wollongong NSW 2522 Australia
| | | | - Stéphanie Corde
- Centre for Medical Radiation Physics; University of Wollongong; Wollongong NSW 2522 Australia
- Prince of Wales Hospital; Sydney NSW Australia
| | - Michael Lerch
- Centre for Medical Radiation Physics; University of Wollongong; Wollongong NSW 2522 Australia
- Illawarra Health Medical Research Institute; Wollongong NSW Australia
| | - Anatoly B. Rosenfeld
- Centre for Medical Radiation Physics; University of Wollongong; Wollongong NSW 2522 Australia
- Illawarra Health Medical Research Institute; Wollongong NSW Australia
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Benmakhlouf H, Andreo P. Spectral distribution of particle fluence in small field detectors and its implication on small field dosimetry. Med Phys 2017; 44:713-724. [DOI: 10.1002/mp.12042] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2016] [Revised: 11/14/2016] [Accepted: 11/27/2016] [Indexed: 11/07/2022] Open
Affiliation(s)
- Hamza Benmakhlouf
- Department of Medical Radiation Physics and Nuclear Medicine; Karolinska University Hospital; SE-17176 Stockholm Sweden
| | - Pedro Andreo
- Department of Medical Radiation Physics and Nuclear Medicine; Karolinska University Hospital; SE-17176 Stockholm Sweden
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Andreo P, Benmakhlouf H. Role of the density, density effect and mean excitation energy in solid-state detectors for small photon fields. Phys Med Biol 2017; 62:1518-1532. [DOI: 10.1088/1361-6560/aa562e] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Looe HK, Harder D, Poppe B. The energy dependence of the lateral dose response functions of detectors with various densities in photon-beam dosimetry. Phys Med Biol 2017; 62:N32-N44. [DOI: 10.1088/1361-6560/aa54aa] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Jong WL, Ung NM, Vannyat A, Jamalludin Z, Rosenfeld A, Wong JHD. “Edge-on” MOSkin detector for stereotactic beam measurement and verification. Phys Med 2017; 33:127-135. [DOI: 10.1016/j.ejmp.2016.12.020] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/14/2016] [Revised: 12/16/2016] [Accepted: 12/29/2016] [Indexed: 11/25/2022] Open
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Small field output factors evaluation with a microDiamond detector over 30 Italian centers. Phys Med 2016; 32:1644-1650. [DOI: 10.1016/j.ejmp.2016.10.017] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/19/2016] [Revised: 10/25/2016] [Accepted: 10/26/2016] [Indexed: 11/18/2022] Open
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Pasquino M, Cutaia C, Radici L, Valzano S, Gino E, Cavedon C, Stasi M. Dosimetric characterization and behaviour in small X-ray fields of a microchamber and a plastic scintillator detector. Br J Radiol 2016; 90:20160596. [PMID: 27826990 DOI: 10.1259/bjr.20160596] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Abstract
OBJECTIVE The aim of this work was to investigate the main dosimetric characteristics and the performance of an A26 Exradin ionization microchamber (A26 IC) and a W1 Exradin plastic scintillation detector (W1 PSD) in small photon beam dosimetry for treatment planning system commissioning and quality assurance programme. METHODS Detector characterization measurements (short-term stability, dose linearity, angular dependence and energy dependence) were performed in water for field sizes up to 10 × 10 cm2. Polarity effect (Ppol) was examined for the A26 IC. The behaviour of the detectors in small field relative dosimetry [percentage depth dose, dose profiles often called the off-axis ratio and output factors (OFs)] was investigated for field sizes ranging from 1 × 1 to 3 × 3 cm2. RESULTS Results were compared with those obtained with other detectors we already use for small photon beam dosimetry. A26 IC and W1 PSD showed a linear dose response. While the A26 IC showed no energy dependence, the W1 PSD showed energy dependence within 2%; no angular dependence was registered. Ppol values for A26 IC were below 0.9% (0.5% for field size >2 × 2 cm2). A26 IC and W1 PSD depth-dose curves and lateral profiles agreed with those obtained with an EDGE diode. No differences were observed among the detectors in OF measurement for field sizes larger than 1 × 1 cm2, with average differences <1%. For field sizes <1 × 1 cm2, the effective volume of ionization chamber and non-water equivalence of EDGE diode become significant. A26 IC OF values were significantly lower than EDGE diode and W1 PSD values, with percentage differences of about -23 and -13% for the smallest field, respectively. W1 PSD OF values lay between ion chambers and diode values, with a maximum percentage difference of about -10% with respect to the EDGE diode, for a 6 × 6-mm2 field size. CONCLUSION The results of our investigation confirm that A26 IC and W1 PSD could play an important role in small field relative dosimetry. Advances in knowledge: Dosimetric characteristics of Exradin A26 ionization microchamber and W1 plastic scintillation detector for small field dosimetry.
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Affiliation(s)
- Massimo Pasquino
- 1 Medical Physics Department, AO Ordine Mauriziano di Torino, Turin, Italy
| | - Claudia Cutaia
- 1 Medical Physics Department, AO Ordine Mauriziano di Torino, Turin, Italy
| | - Lorenzo Radici
- 1 Medical Physics Department, AO Ordine Mauriziano di Torino, Turin, Italy
| | - Serena Valzano
- 1 Medical Physics Department, AO Ordine Mauriziano di Torino, Turin, Italy
| | - Eva Gino
- 1 Medical Physics Department, AO Ordine Mauriziano di Torino, Turin, Italy
| | - Carlo Cavedon
- 2 Medical Physics Department, University Hospital, Verona, Italy
| | - Michele Stasi
- 1 Medical Physics Department, AO Ordine Mauriziano di Torino, Turin, Italy
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Qin Y, Zhong H, Wen N, Snyder K, Huang Y, Chetty IJ. Deriving detector-specific correction factors for rectangular small fields using a scintillator detector. J Appl Clin Med Phys 2016; 17:379-391. [PMID: 27929510 PMCID: PMC5690516 DOI: 10.1120/jacmp.v17i6.6433] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2016] [Revised: 08/30/2016] [Accepted: 08/29/2016] [Indexed: 11/23/2022] Open
Abstract
The goal of this study was to investigate small field output factors (OFs) for flattening filter‐free (FFF) beams on a dedicated stereotactic linear accelerator‐based system. From this data, the collimator exchange effect was quantified, and detector‐specific correction factors were generated. Output factors for 16 jaw‐collimated small fields (from 0.5 to 2 cm) were measured using five different detectors including an ion chamber (CC01), a stereotactic field diode (SFD), a diode detector (Edge), Gafchromic film (EBT3), and a plastic scintillator detector (PSD, W1). Chamber, diodes, and PSD measurements were performed in a Wellhofer water tank, while films were irradiated in solid water at 100 cm source‐to‐surface distance and 10 cm depth. The collimator exchange effect was quantified for rectangular fields. Monte Carlo (MC) simulations of the measured configurations were also performed using the EGSnrc/DOSXYZnrc code. Output factors measured by the PSD and verified against film and MC calculations were chosen as the benchmark measurements. Compared with plastic scintillator detector (PSD), the small volume ion chamber (CC01) underestimated output factors by an average of ‐1.0%±4.9%(max.=‐11.7% for 0.5×0.5cm2 square field). The stereotactic diode (SFD) overestimated output factors by 2.5%±0.4%(max.=3.3% for 0.5×1cm2 rectangular field). The other diode detector (Edge) also overestimated the OFs by an average of 4.2%±0.9%(max.=6.0% for 1×1cm2 square field). Gafchromic film (EBT3) measurements and MC calculations agreed with the scintillator detector measurements within 0.6%±1.8% and 1.2%±1.5%, respectively. Across all the X and Y jaw combinations, the average collimator exchange effect was computed: 1.4%±1.1% (CC01), 5.8%±5.4% (SFD), 5.1%±4.8% (Edge diode), 3.5%±5.0% (Monte Carlo), 3.8%±4.7% (film), and 5.5%±5.1% (PSD). Small field detectors should be used with caution with a clear understanding of their behaviors, especially for FFF beams and small, elongated fields. The scintillator detector exhibited good agreement against Gafchromic film measurements and MC simulations over the range of field sizes studied. The collimator exchange effect was found to be important at these small field sizes. Detector‐specific correction factors were computed using the scintillator measurements as the benchmark. PACS number(s): 87.56.Fc
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Park K, Bak J, Park S, Choi W, Park SW. Determination of small-field correction factors for cylindrical ionization chambers using a semiempirical method. Phys Med Biol 2016; 61:1293-308. [PMID: 26796623 DOI: 10.1088/0031-9155/61/3/1293] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
A semiempirical method based on the averaging effect of the sensitive volumes of different air-filled ionization chambers (ICs) was employed to approximate the correction factors for beam quality produced from the difference in the sizes of the reference field and small fields.We measured the output factors using several cylindrical ICs and calculated the correction factors using a mathematical method similar to deconvolution; in the method, we modeled the variable and inhomogeneous energy fluence function within the chamber cavity. The parameters of the modeled function and the correction factors were determined by solving a developed system of equations as well as on the basis of the measurement data and the geometry of the chambers. Further, Monte Carlo (MC) computations were performed using the Monaco® treatment planning system to validate the proposed method.The determined correction factors () were comparable to the values derived from the MC computations performed using Monaco®. For example, for a 6 MV photon beam and a field size of 1 × 1 cm2, was calculated to be for a PTW 31010 chamber and for a PTW 31016 chamber. On the other hand, the values determined from the MC computations were 1.121 and 1.031, respectively; the difference between the proposed method and the MC computation is less than 2%. In addition, we determined the values for PTW 30013, PTW 31010, PTW 31016, IBA FC23-C, and IBA CC13 chambers as well.We devised a method for determining from both the measurement of the output factors and model-based mathematical computation. The proposed method can be useful in case the MC simulation would not be applicable for the clinical settings.
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Beaulieu L, Beddar S. Review of plastic and liquid scintillation dosimetry for photon, electron, and proton therapy. Phys Med Biol 2016; 61:R305-R343. [DOI: 10.1088/0031-9155/61/20/r305] [Citation(s) in RCA: 97] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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