1
|
Georgiou G, Kumar S, Würfel JU, Gilmore M, Underwood TSA, Rowbottom CG, Fenwick JD. The PTW microSilicon diode: Performance in small 6 and 15 MV photon fields and utility of density compensation. Med Phys 2021; 48:8062-8074. [PMID: 34725831 DOI: 10.1002/mp.15329] [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: 03/10/2021] [Revised: 10/12/2021] [Accepted: 10/13/2021] [Indexed: 11/11/2022] Open
Abstract
PURPOSE We have experimentally and computationally characterized the PTW microSilicon 60023-type diode's performance in 6 and 15 MV photon fields ≥5 × 5 mm2 projected to isocenter. We tested the detector on- and off-axis at 5 and 15 cm depths in water, and investigated whether its response could be improved by including within it a thin airgap. METHODS Experimentally, detector readings were taken in fields generated by a Varian TrueBeam linac and compared with doses-to-water measured using Gafchromic film and ionization chambers. An unmodified 60023-type diode was tested along with detectors modified to include 0.6, 0.8, and 1.0 mm thick airgaps. Computationally, doses absorbed by water and detectors' sensitive volumes were calculated using the EGSnrc/BEAMnrc Monte Carlo radiation transport code. Detector response was characterized using k Q c l i n , 4 cm f c l i n , 4 cm , a factor that corrects for differences in the ratio of dose-to-water to detector reading between small fields and the reference condition, in this study 5 cm deep on-axis in a 4 × 4 cm2 field. RESULTS The greatest errors in measurements of small field doses made using uncorrected readings from the unmodified 60023-type detector were over-responses of 2.6% ± 0.5% and 5.3% ± 2.0% determined computationally and experimentally, relative to the reading-per-dose in the reference field. Corresponding largest errors for the earlier 60017-type detector were 11.9% ± 0.6% and 11.7% ± 1.4% over-responses. Adding even the thinnest, 0.6 mm, airgap to the 60023-type detector over-corrected it, leading to under-responses of up to 4.8% ± 0.6% and 5.0% ± 1.8% determined computationally and experimentally. Further, Monte Carlo calculations indicate that a detector with a 0.3 mm airgap would read correctly to within 1.3% on-axis. The ratio of doses at 15 and 5 cm depths in water in a 6 MV 4 × 4 cm2 field was measured more accurately using the unmodified 60023-type detector than using the 60017-type detector, and was within 0.3% of the ratio measured using an ion chamber. The 60023-type diode's sensitivity also varied negligibly as dose-rate was reduced from 13 to 4 Gy min-1 by decreasing the linac pulse repetition frequency, whereas the sensitivity of the 60017-type detector fell by 1.5%. CONCLUSIONS The 60023-type detector performed well in small fields across a wide range of beam energies, field sizes, depths, and off-axis positions. Its response can potentially be further improved by adding a thin, 0.3 mm, airgap.
Collapse
Affiliation(s)
- Georgios Georgiou
- Department of Molecular and Clinical Cancer Medicine, Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool, UK.,Department of Physics, Clatterbridge Cancer Centre, Wirral, UK.,Department of Physics, Oliver Lodge Laboratory, University of Liverpool, Liverpool, UK
| | - Sudhir Kumar
- Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, Mumbai, India
| | | | - Martyn Gilmore
- Department of Physics, Clatterbridge Cancer Centre, Wirral, UK
| | - Tracy S A Underwood
- Division of Cancer Sciences, School of Medical Sciences, Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, UK
| | - Carl G Rowbottom
- Department of Physics, Clatterbridge Cancer Centre, Wirral, UK.,Department of Physics, Oliver Lodge Laboratory, University of Liverpool, Liverpool, UK
| | - John D Fenwick
- Department of Molecular and Clinical Cancer Medicine, Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool, UK.,Department of Physics, Clatterbridge Cancer Centre, Wirral, UK
| |
Collapse
|
2
|
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: 53] [Impact Index Per Article: 17.7] [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.
Collapse
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
| |
Collapse
|
3
|
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: 1] [Impact Index Per Article: 0.3] [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.
Collapse
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
| |
Collapse
|
4
|
Aland T, Jarema T, Trapp JV, Kairn T. Patient-specific quality assurance on a Varian Halcyon linear accelerator using a PTW Octavius 4D device. Phys Eng Sci Med 2021; 44:565-572. [PMID: 33704691 DOI: 10.1007/s13246-021-00986-4] [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: 12/07/2020] [Accepted: 02/25/2021] [Indexed: 11/25/2022]
Abstract
This study investigates and validates the use of the Octavius 4D system for patient specific quality assurance on Halcyon, which is capable of rotating at 4 revolutions per minute (RPM). A commercially available PTW Octavius 4D system was used for this study which had a maximum rotation speed of 3 RPM. Initial validation included testing the accuracy of the inclinometer, percent depth doses (PDD), output factors, and dose profiles for selected static square fields. The same static fields were also subject to a gamma comparison with the TPS. This was followed by an evaluation of twelve clinical treatment plans and seven non-clinical plans with varying gantry rotation speeds. All testing was completed using detector array measurement times of 200 ms and 100 ms. Inclinometer accuracy was within 0.3° of actual gantry angle. Output factors varied less than 0.6%, PDD differences were no greater than 1.4%, and dose profile differences were less than 2.2%. Gamma pass rates for the static fields were 96.7% (2%/2mm) and 99.7% (3%/3mm). A prototype control unit, which had a maximum rotation speed of 4 RPM was also used to test the clinical and non-clinical plans. For the clinical plans, the mean gamma pass rates (2%/2mm) were 86.1% and 88.1% for the commercial unit and prototype unit respectively. Results using a measurement time of 200 ms were superior to those using 100 ms. For Halcyon deliveries greater than 3 RPM, worst case gamma results for the commercial unit were 28.6% compared to 98.5% using the prototype unit. Accurate patient specific quality assurance results can be obtained using the Octavius 4D system with a Halcyon linac, provided that the system measurement time is kept at 200 ms and the rotation speed of Halycon does not exceed 3 RPM. For higher RPM deliveries, an Octavius 4D unit with 4 RPM rotation capability is recommended.
Collapse
Affiliation(s)
- T Aland
- Icon Group, 22 Cordelia Street, South Brisbane, QLD, 4101, Australia.
- School of Chemistry, Physics, and Mechanical Engineering, Queensland University of Technology, GPO Box 2434, Brisbane, QLD, 4000, Australia.
| | - T Jarema
- Icon Group, 22 Cordelia Street, South Brisbane, QLD, 4101, Australia
| | - J V Trapp
- School of Chemistry, Physics, and Mechanical Engineering, Queensland University of Technology, GPO Box 2434, Brisbane, QLD, 4000, Australia
| | - T Kairn
- School of Chemistry, Physics, and Mechanical Engineering, Queensland University of Technology, GPO Box 2434, Brisbane, QLD, 4000, Australia
- Cancer Care Services, Royal Brisbane and Women's Hospital, Herston, QLD, Australia
- School of Information Technology and Electrical Engineering, University of Queensland, St Lucia, QLD, 4072, Australia
| |
Collapse
|
5
|
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.
Collapse
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
| |
Collapse
|
6
|
Rosenfeld AB, Biasi G, Petasecca M, Lerch MLF, Villani G, Feygelman V. Semiconductor dosimetry in modern external-beam radiation therapy. Phys Med Biol 2020; 65:16TR01. [PMID: 32604077 DOI: 10.1088/1361-6560/aba163] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
|
7
|
Georgiou G, Kumar S, Würfel JU, Underwood TSA, Thompson JM, Hill MA, Rowbottom CG, Fenwick JD. Density compensated diodes for small field dosimetry: comprehensive testing and implications for design. Phys Med Biol 2020; 65:155011. [PMID: 32392539 DOI: 10.1088/1361-6560/ab91d9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
PURPOSE In small megavoltage photon fields, the accuracies of an unmodified PTW 60017-type diode dosimeter and six diodes modified by adding airgaps of thickness 0.6-1.6 mm and diameter 3.6 mm have been comprehensively characterized experimentally and computationally. The optimally thick airgap for density compensation was determined, and detectors were micro-CT imaged to investigate differences between experimentally measured radiation responses and those predicted computationally. METHODS Detectors were tested on- and off-axis, at 5 and 15 cm depths in 6 and 15 MV fields ≥ 0.5 × 0.5 cm2. Computational studies were carried out using the EGSnrc/BEAMnrc Monte Carlo radiation transport code. Experimentally, radiation was delivered using a Varian TrueBeam linac and doses absorbed by water were measured using Gafchromic EBT3 film and ionization chambers, and compared with diode readings. Detector response was characterized via the [Formula: see text] formalism, choosing a 4 × 4 cm2 reference field. RESULTS For the unmodified 60017 diode, the maximum error in small field doses obtained from diode readings uncorrected by [Formula: see text] factors was determined as 11.9% computationally at +0.25 mm off-axis and 5 cm depth in a 15 MV 0.5 × 0.5 cm2 field, and 11.7% experimentally at -0.30 mm off-axis and 5 cm depth in the same field. A detector modified to include a 1.6 mm thick airgap performed best, with maximum computationally and experimentally determined errors of 2.2% and 4.1%. The 1.6 mm airgap deepened the modified dosimeter's effective point of measurement by 0.5 mm. For some detectors significant differences existed between responses in small fields determined computationally and experimentally, micro-CT imaging indicating that these differences were due to within-tolerance variations in the thickness of an epoxy resin layer. CONCLUSIONS The dosimetric performance of a 60017 diode detector was comprehensively improved throughout 6 and 15 MV small photon fields via density compensation. For this approach to work well with good detector-to-detector reproducibility, tolerances on dense component dimensions should be reduced to limit associated variations of response in small fields, or these components should be modified to have more water-like densities.
Collapse
Affiliation(s)
- Georgios Georgiou
- Department of Molecular and Clinical Cancer Medicine, Institute of Translational Medicine, University of Liverpool, The Sherrington Building, Ashton Street, Liverpool L69 3BX, United Kingdom. Department of Physics, Clatterbridge Cancer Centre, Clatterbridge Road, Wirral CH63 4JY, United Kingdom. Department of Physics, University of Liverpool, Oliver Lodge Laboratory, Oxford Street, Liverpool L69 7ZE, United Kingdom
| | | | | | | | | | | | | | | |
Collapse
|
8
|
Maxwell SK, Charles PH, Cassim N, Kairn T, Crowe SB. Assessing the fit of 3D printed bolus from CT, optical scanner and photogrammetry methods. Phys Eng Sci Med 2020; 43:601-607. [PMID: 32524442 DOI: 10.1007/s13246-020-00861-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2019] [Accepted: 03/17/2020] [Indexed: 11/30/2022]
Abstract
Bolus plays an important role in the radiation therapy of superficial lesions and the application of 3D printing to its design can improve fit and dosimetry. This study quantitatively compares the fits of boluses designed from different imaging modalities. A head phantom was imaged using three systems: a CT simulator, a 3D optical scanner, and an interchangeable lens camera. Nose boluses were designed and 3D printed from each modality. A 3D printed phantom with air gaps of known thicknesses was used to calibrate mean HU to measure air gaps of unknown thickness and assess the fit of each bolus on the head phantom. The bolus created from the optical scanner data resulted in the best fit, with a mean air gap of 0.16 mm. Smoothing of the CT bolus resulted in a more clinically suitable model, comparable to that from the optical scanner method. The bolus produced from the photogrammetry method resulted in air gaps larger than 1 mm in thickness. The use of optical scanner and photogrammetry models have many advantages over the conventional bolus-from-CT method, however workflow should be refined to ensure accuracy if implemented clinically.
Collapse
Affiliation(s)
- S K Maxwell
- Royal Brisbane and Women's Hospital, Brisbane, QLD, Australia.
| | - P H Charles
- Herston Biofabrication Institute, Brisbane, QLD, Australia.,Queensland University of Technology, Brisbane, QLD, Australia
| | - N Cassim
- Royal Brisbane and Women's Hospital, Brisbane, QLD, Australia
| | - T Kairn
- Royal Brisbane and Women's Hospital, Brisbane, QLD, Australia.,Queensland University of Technology, Brisbane, QLD, Australia
| | - S B Crowe
- Royal Brisbane and Women's Hospital, Brisbane, QLD, Australia.,Queensland University of Technology, Brisbane, QLD, Australia
| |
Collapse
|
9
|
Stansook N, Biasi G, Utitsarn K, Petasecca M, Metcalfe P, Carolan M, Lerch MLF, Perevertaylo VL, Kron T, Rosenfeld AB. 2D monolithic silicon-diode array detectors in megavoltage photon beams: does the fabrication technology matter? A medical physicist's perspective. AUSTRALASIAN PHYSICAL & ENGINEERING SCIENCES IN MEDICINE 2019; 42:443-451. [PMID: 30790139 DOI: 10.1007/s13246-019-00736-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/24/2018] [Accepted: 02/19/2019] [Indexed: 01/24/2023]
Abstract
A family of prototype 2D monolithic silicon-diode array detectors (MP512, Duo, Octa) has been proposed by the Centre for Medical Radiation Physics, University of Wollongong (Australia) for relative dosimetry in small megavoltage photon beams. These detectors, which differ in the topology of their 512 sensitive volumes, were originally fabricated on bulk p-type substrates. More recently, they have also been fabricated on epitaxial p-type substrates. In the literature, their performance has been individually characterized for quality assurance (QA) applications. The present study directly assessed and compared that of a MP512-bulk and that of a MP512-epitaxial in terms of radiation hardness, long-term stability, response linearity with dose, dose per pulse and angular dependence. Their measurements of output factors, off-axis ratios and percentage depth doses in square radiation fields collimated by the jaws and produced by 6 MV and 10 MV flattened photon beams were then benchmarked against those by commercially available detectors. The present investigation was aimed at establishing, from a medical physicist's perspective, how the bulk and epitaxial fabrication technologies would affect the implementation of the MP512s into a QA protocol. Based on results, the MP512-epitaxial would offer superior radiation hardness, long-term stability and achievable uniformity and reproducibility of the response across the 2D active area.
Collapse
Affiliation(s)
- N Stansook
- Centre for Medical Radiation Physics (CMRP), University of Wollongong, Wollongong, Australia.,Department of Radiology, Faculty of Medicine, Mahidol University, Bangkok, Thailand
| | - G Biasi
- Centre for Medical Radiation Physics (CMRP), University of Wollongong, Wollongong, Australia
| | - K Utitsarn
- Centre for Medical Radiation Physics (CMRP), University of Wollongong, Wollongong, Australia.,Department of Medical Services, Lopburi Cancer Hospital, Lopburi, Thailand
| | - M Petasecca
- Centre for Medical Radiation Physics (CMRP), University of Wollongong, Wollongong, Australia.,Illawarra Health and Medical Research Institute (IHMRI), Wollongong, Australia
| | - P Metcalfe
- Centre for Medical Radiation Physics (CMRP), University of Wollongong, Wollongong, Australia
| | - M Carolan
- Illawarra Health and Medical Research Institute (IHMRI), Wollongong, Australia.,Illawarra Cancer Care Centre (ICCC), Wollongong, Australia
| | - M L F Lerch
- Centre for Medical Radiation Physics (CMRP), University of Wollongong, Wollongong, Australia.,Illawarra Health and Medical Research Institute (IHMRI), Wollongong, Australia
| | | | - T Kron
- Centre for Medical Radiation Physics (CMRP), University of Wollongong, Wollongong, Australia.,Peter MacCallum Cancer Centre, Melbourne, Australia.,Sir Peter MacCallum Cancer Institute, University of Melbourne, Melbourne, Australia
| | - A B Rosenfeld
- Centre for Medical Radiation Physics (CMRP), University of Wollongong, Wollongong, Australia. .,Illawarra Health and Medical Research Institute (IHMRI), Wollongong, Australia.
| |
Collapse
|
10
|
Biasi G, Petasecca M, Guatelli S, Martin EA, Grogan G, Hug B, Lane J, Perevertaylo V, Kron T, Rosenfeld AB. CyberKnife ® fixed cone and Iris™ defined small radiation fields: Assessment with a high-resolution solid-state detector array. J Appl Clin Med Phys 2018; 19:547-557. [PMID: 29998618 PMCID: PMC6123130 DOI: 10.1002/acm2.12414] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2018] [Revised: 05/13/2018] [Accepted: 06/18/2018] [Indexed: 11/18/2022] Open
Abstract
Purpose The challenges of accurate dosimetry for stereotactic radiotherapy (SRT) with small unflattened radiation fields have been widely reported in the literature. In this case, suitable dosimeters would have to offer a submillimeter spatial resolution. The CyberKnife® (Accuray Inc., Sunnyvale, CA, USA) is an SRT‐dedicated linear accelerator (linac), which can deliver treatments with submillimeter positional accuracy using circular fields. Beams are delivered with the desired field size using fixed cones, the InCise™ multileaf collimator or a dynamic variable‐aperture Iris™ collimator. The latter, allowing for field sizes to be varied during treatment delivery, has the potential to decrease treatment time, but its reproducibility in terms of output factors (OFs) and dose profiles (DPs) needs to be verified. Methods A 2D monolithic silicon array detector, the “Octa”, was evaluated for dosimetric quality assurance (QA) for a CyberKnife system. OFs, DPs, percentage depth‐dose (PDD) and tissue maximum ratio (TMR) were investigated, and results were benchmarked against the PTW SRS diode. Cross‐plane, in‐plane and 2 diagonal dose profiles were measured simultaneously with high spatial resolution (0.3 mm). Monte Carlo (MC) simulations with a GEANT4 (GEometry ANd Tracking 4) tool‐kit were added to the study to support the experimental characterization of the detector response. Results For fixed cones and the Iris, for all field sizes investigated in the range between 5 and 60 mm diameter, OFs, PDDs, TMRs, and DPs in terms of FWHM measured by the Octa were accurate within 3% when benchmarked against the SRS diode and MC calculations. Conclusions The Octa was shown to be an accurate dosimeter for measurements with a 6 MV FFF beam delivered with a CyberKnife system. The detector enabled real‐time dosimetric verification for the variable aperture Iris collimator, yielding OFs and DPs consistent with those obtained with alternative methods.
Collapse
Affiliation(s)
- Giordano Biasi
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, 2522 NSW, Australia
| | - Marco Petasecca
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, 2522 NSW, Australia
| | - Susanna Guatelli
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, 2522 NSW, Australia
| | - Ebert A Martin
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, 2522 NSW, Australia.,Department of Radiation Oncology, Sir Charles Gairdner Hospital, Nedlands, WA, Australia.,School of Physics and Astrophysics, University of Western Australia, Crawley, WA, Australia
| | - Garry Grogan
- Department of Radiation Oncology, Sir Charles Gairdner Hospital, Nedlands, WA, Australia
| | - Benjamin Hug
- Department of Radiation Oncology, Sir Charles Gairdner Hospital, Nedlands, WA, Australia.,School of Physics and Astrophysics, University of Western Australia, Crawley, WA, Australia
| | - Jonathan Lane
- Department of Radiation Oncology, Sir Charles Gairdner Hospital, Nedlands, WA, Australia
| | | | - Tomas Kron
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, 2522 NSW, Australia.,Peter MacCallum Cancer Centre, Melbourne, VIC, Australia.,Sir Peter MacCallum Cancer Institute, University of Melbourne, Melbourne, VIC, Australia
| | - Anatoly B Rosenfeld
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, 2522 NSW, Australia
| |
Collapse
|
11
|
Biasi G, Petasecca M, Guatelli S, Hardcastle N, Carolan M, Perevertaylo V, Kron T, Rosenfeld AB. A novel high-resolution 2D silicon array detector for small field dosimetry with FFF photon beams. Phys Med 2017; 45:117-126. [PMID: 29472075 DOI: 10.1016/j.ejmp.2017.12.010] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/11/2017] [Revised: 12/13/2017] [Accepted: 12/15/2017] [Indexed: 11/19/2022] Open
Abstract
PURPOSE Flattening filter free (FFF) beams are increasingly being considered for stereotactic radiotherapy (SRT). For the first time, the performance of a monolithic silicon array detector under 6 and 10 MV FFF beams was evaluated. The dosimeter, named "Octa" and designed by the Centre for Medical Radiation Physics (CMRP), was tested also under flattened beams for comparison. METHODS Output factors (OFs), percentage depth-dose (PDD), dose profiles (DPs) and dose per pulse (DPP) dependence were investigated. Results were benchmarked against commercially available detectors for small field dosimetry. RESULTS The dosimeter was shown to be a 'correction-free' silicon array detector for OFs and PDD measurements for all the beam qualities investigated. Measured OFs were accurate within 3% and PDD values within 2% compared against the benchmarks. Cross-plane, in-plane and diagonal DPs were measured simultaneously with high spatial resolution (0.3 mm) and real time read-out. A DPP dependence (24% at 0.021 mGy/pulse relative to 0.278 mGy/pulse) was found and could be easily corrected for in the case of machine specific quality assurance applications. CONCLUSIONS Results were consistent with those for monolithic silicon array detectors designed by the CMRP and previously characterized under flattened beams only, supporting the robustness of this technology for relative dosimetry for a wide range of beam qualities and dose per pulses. In contrast to its predecessors, the design of the Octa offers an exhaustive high-resolution 2D dose map characterization, making it a unique real-time radiation detector for small field dosimetry for field sizes up to 3 cm side.
Collapse
Affiliation(s)
- G Biasi
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia
| | - M Petasecca
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia
| | - S Guatelli
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia
| | - N Hardcastle
- Peter MacCallum Cancer Centre, Melbourne, Australia
| | - M Carolan
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia; Illawarra Cancer Care Centre, Wollongong Hospital, Wollongong, NSW, Australia
| | | | - T Kron
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia; Peter MacCallum Cancer Centre, Melbourne, Australia; Sir Peter MacCallum Cancer Institute, University of Melbourne, Australia
| | - A B Rosenfeld
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia.
| |
Collapse
|
12
|
Zoros E, Moutsatsos A, Pappas EP, Georgiou E, Kollias G, Karaiskos P, Pantelis E. Monte Carlo and experimental determination of correction factors for gamma knife perfexion small field dosimetry measurements. Phys Med Biol 2017; 62:7532-7555. [PMID: 28796643 DOI: 10.1088/1361-6560/aa8590] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Detector-, field size- and machine-specific correction factors are required for precise dosimetry measurements in small and non-standard photon fields. In this work, Monte Carlo (MC) simulation techniques were used to calculate the [Formula: see text] and [Formula: see text] correction factors for a series of ionization chambers, a synthetic microDiamond and diode dosimeters, used for reference and/or output factor (OF) measurements in the Gamma Knife Perfexion photon fields. Calculations were performed for the solid water (SW) and ABS plastic phantoms, as well as for a water phantom of the same geometry. MC calculations for the [Formula: see text] correction factors in SW were compared against corresponding experimental results for a subset of ionization chambers and diode detectors. Reference experimental OF data were obtained through the weighted average of corresponding measurements using TLDs, EBT-2 films and alanine pellets. [Formula: see text] values close to unity (within 1%) were calculated for most of ionization chambers in water. Greater corrections of up to 6.0% were observed for chambers with relatively large air-cavity dimensions and steel central electrode. A phantom correction of 1.006 and 1.024 (breaking down to 1.014 from the ABS sphere and 1.010 from the accompanying ABS phantom adapter) were calculated for the SW and ABS phantoms, respectively, adding up to [Formula: see text] corrections in water. Both measurements and MC calculations for the diode and microDiamond detectors resulted in lower than unit [Formula: see text] correction factors, due to their denser sensitive volume and encapsulation materials. In comparison, higher than unit [Formula: see text] results for the ionization chambers suggested field size depended dose underestimations (being significant for the 4 mm field), with magnitude depending on the combination of contradicting phenomena associated with volume averaging and electron fluence perturbations. Finally, the presence of 0.5 mm air-gap between the diodes' frontal surface and their phantom-inserts may considerably influence OF measurements, reaching 4.6% for the Razor diode.
Collapse
Affiliation(s)
- E Zoros
- Medical Physics Laboratory, Medical School, National and Kapodistrian University of Athens, 75 Mikras Asias, 115 27 Athens, Greece
| | | | | | | | | | | | | |
Collapse
|
13
|
Perrett B, Charles P, Markwell T, Kairn T, Crowe S. Feasibility of 3D printed air slab diode caps for small field dosimetry. AUSTRALASIAN PHYSICAL & ENGINEERING SCIENCES IN MEDICINE 2017; 40:631-642. [DOI: 10.1007/s13246-017-0570-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2016] [Accepted: 07/04/2017] [Indexed: 10/19/2022]
|
14
|
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.
Collapse
|
15
|
Effects of inaccurate small field dose measurements on calculated treatment doses. AUSTRALASIAN PHYSICAL & ENGINEERING SCIENCES IN MEDICINE 2016; 39:747-53. [DOI: 10.1007/s13246-016-0461-y] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/24/2016] [Accepted: 06/23/2016] [Indexed: 12/31/2022]
|
16
|
Kron T, Lehmann J, Greer PB. Dosimetry of ionising radiation in modern radiation oncology. Phys Med Biol 2016; 61:R167-205. [DOI: 10.1088/0031-9155/61/14/r167] [Citation(s) in RCA: 68] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
|
17
|
Study of commercial detector responses in non-equilibrium small photon fields of a 1000 MU/min CyberKnife system. Phys Med 2016; 32:818-25. [DOI: 10.1016/j.ejmp.2016.05.052] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/26/2016] [Revised: 05/09/2016] [Accepted: 05/10/2016] [Indexed: 11/30/2022] Open
|
18
|
Tyler MK, Liu PZY, Lee C, McKenzie DR, Suchowerska N. Small field detector correction factors: effects of the flattening filter for Elekta and Varian linear accelerators. J Appl Clin Med Phys 2016; 17:223-235. [PMID: 27167280 PMCID: PMC5690940 DOI: 10.1120/jacmp.v17i3.6059] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2015] [Revised: 01/12/2016] [Accepted: 01/11/2016] [Indexed: 11/24/2022] Open
Abstract
Flattening filter‐free (FFF) beams are becoming the preferred beam type for stereotactic radiosurgery (SRS) and stereotactic ablative radiation therapy (SABR), as they enable an increase in dose rate and a decrease in treatment time. This work assesses the effects of the flattening filter on small field output factors for 6 MV beams generated by both Elekta and Varian linear accelerators, and determines differences between detector response in flattened (FF) and FFF beams. Relative output factors were measured with a range of detectors (diodes, ionization chambers, radiochromic film, and microDiamond) and referenced to the relative output factors measured with an air core fiber optic dosimeter (FOD), a scintillation dosimeter developed at Chris O'Brien Lifehouse, Sydney. Small field correction factors were generated for both FF and FFF beams. Diode measured detector response was compared with a recently published mathematical relation to predict diode response corrections in small fields. The effect of flattening filter removal on detector response was quantified using a ratio of relative detector responses in FFF and FF fields for the same field size. The removal of the flattening filter was found to have a small but measurable effect on ionization chamber response with maximum deviations of less than ±0.9% across all field sizes measured. Solid‐state detectors showed an increased dependence on the flattening filter of up to ±1.6%. Measured diode response was within ±1.1% of the published mathematical relation for all fields up to 30 mm, independent of linac type and presence or absence of a flattening filter. For 6 MV beams, detector correction factors between FFF and FF beams are interchangeable for a linac between FF and FFF modes, providing that an additional uncertainty of up to ±1.6% is accepted. PACS number(s): 87.55.km, 87.56.bd, 87.56.Da
Collapse
|
19
|
Brualla-González L, Gómez F, Pombar M, Pardo-Montero J. Dose rate dependence of the PTW 60019 microDiamond detector in high dose-per-pulse pulsed beams. Phys Med Biol 2015; 61:N11-9. [PMID: 26625177 DOI: 10.1088/0031-9155/61/1/n11] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Recombination effects can affect the detectors used for the dosimetry of radiotherapy fields. They are important when using ionization chambers, especially in liquid-filled ionization chambers, and should be corrected for. The introduction of flattening-filter-free accelerators increases the typical dose-per-pulse used in radiotherapy beams, which leads to more important recombination effects. Diamond detectors provide a good solution for the dosimetry and quality assurance of small radiotherapy fields, due to their low energy dependence and small volume. The group of Università di Roma Tor Vergata has developed a synthetic diamond detector, which is commercialized by PTW as microDiamond detector type 60019. In this work we present an experimental characterization of the collection efficiency of the microDiamond detector, focusing on high dose-per-pulse FFF beams. The collection efficiency decreases with dose-per-pulse, down to 0.978 at 2.2 mGy/pulse, following a Fowler-Attix-like curve. On the other hand, we have found no significant dependence of the collection efficiency on the pulse repetition frequency (or pulse period).
Collapse
Affiliation(s)
- Luis Brualla-González
- Servicio de Radiofísica, ERESA, Hospital General Universitario de Valencia, 46014 València, Spain
| | | | | | | |
Collapse
|
20
|
Kumar S, Fenwick JD, Underwood TSA, Deshpande DD, Scott AJD, Nahum AE. Breakdown of Bragg–Gray behaviour for low-density detectors under electronic disequilibrium conditions in small megavoltage photon fields. Phys Med Biol 2015; 60:8187-212. [DOI: 10.1088/0031-9155/60/20/8187] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
|
21
|
Bouchard H, Seuntjens J, Duane S, Kamio Y, Palmans H. Detector dose response in megavoltage small photon beams. I. Theoretical concepts. Med Phys 2015; 42:6033-47. [DOI: 10.1118/1.4930053] [Citation(s) in RCA: 76] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
|
22
|
Petasecca M, Alhujaili S, Aldosari AH, Fuduli I, Newall M, Porumb CS, Carolan M, Nitschke K, Lerch MLF, Kalliopuska J, Perevertaylo V, Rosenfeld AB. Angular independent silicon detector for dosimetry in external beam radiotherapy. Med Phys 2015; 42:4708-18. [DOI: 10.1118/1.4926778] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
|
23
|
Underwood TSA, Thompson J, Bird L, Scott AJD, Patmore P, Winter HC, Hill MA, Fenwick JD. Validation of a prototype DiodeAir for small field dosimetry. Phys Med Biol 2015; 60:2939-53. [DOI: 10.1088/0031-9155/60/7/2939] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
|
24
|
Clinical use of diodes and micro-chambers to obtain accurate small field output factor measurements. AUSTRALASIAN PHYSICAL & ENGINEERING SCIENCES IN MEDICINE 2015; 38:357-67. [DOI: 10.1007/s13246-015-0334-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/08/2014] [Accepted: 02/19/2015] [Indexed: 12/22/2022]
|
25
|
Baluti F, Deloar HM, Lansley SP, Meyer J. Monte Carlo modelling the dosimetric effects of electrode material on diamond detectors. AUSTRALASIAN PHYSICAL & ENGINEERING SCIENCES IN MEDICINE 2015; 38:101-8. [DOI: 10.1007/s13246-015-0329-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/24/2014] [Accepted: 01/07/2015] [Indexed: 10/24/2022]
|
26
|
Charles PH, Cranmer-Sargison G, Thwaites DI, Kairn T, Crowe SB, Pedrazzini G, Aland T, Kenny J, Langton CM, Trapp JV. Design and experimental testing of air slab caps which convert commercial electron diodes into dual purpose, correction-free diodes for small field dosimetry. Med Phys 2014; 41:101701. [DOI: 10.1118/1.4894728] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
|
27
|
Papaconstadopoulos P, Tessier F, Seuntjens J. On the correction, perturbation and modification of small field detectors in relative dosimetry. Phys Med Biol 2014; 59:5937-52. [DOI: 10.1088/0031-9155/59/19/5937] [Citation(s) in RCA: 79] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
|
28
|
Aldosari AH, Petasecca M, Espinoza A, Newall M, Fuduli I, Porumb C, Alshaikh S, Alrowaili ZA, Weaver M, Metcalfe P, Carolan M, Lerch MLF, Perevertaylo V, Rosenfeld AB. A two dimensional silicon detectors array for quality assurance in stereotactic radiotherapy: MagicPlate-512. Med Phys 2014; 41:091707. [DOI: 10.1118/1.4892384] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
|
29
|
Kamio Y, Bouchard H. Correction-less dosimetry of nonstandard photon fields: a new criterion to determine the usability of radiation detectors. Phys Med Biol 2014; 59:4973-5002. [DOI: 10.1088/0031-9155/59/17/4973] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
|
30
|
Moignier C, Huet C, Makovicka L. Determination of the kQclin,Qmsrfclin,fmsr correction factors for detectors used with an 800 MU/min CyberKnife®
system equipped with fixed collimators and a study of detector response to small photon beams using a Monte Carlo method. Med Phys 2014; 41:071702. [DOI: 10.1118/1.4881098] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
|
31
|
Kairn T, Crowe SB, Charles PH, Trapp JV. Using narrow beam profiles to quantify focal spot size, for accurate Monte Carlo simulations of SRS/SRT systems. ACTA ACUST UNITED AC 2014. [DOI: 10.1088/1742-6596/489/1/012014] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
|
32
|
Charles PH, Crowe SB, Kairn T, Knight R, Hill B, Kenny J, Langton CM, Trapp JV. The influence of Monte Carlo source parameters on detector design and dose perturbation in small field dosimetry. ACTA ACUST UNITED AC 2014. [DOI: 10.1088/1742-6596/489/1/012006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
|
33
|
Charles PH, Cranmer-Sargison G, Thwaites DI, Crowe SB, Kairn T, Knight RT, Kenny J, Langton CM, Trapp JV. A practical and theoretical definition of very small field size for radiotherapy output factor measurements. Med Phys 2014; 41:041707. [DOI: 10.1118/1.4868461] [Citation(s) in RCA: 63] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
|
34
|
Lechner W, Palmans H, Sölkner L, Grochowska P, Georg D. Detector comparison for small field output factor measurements in flattening filter free photon beams. Radiother Oncol 2013; 109:356-60. [DOI: 10.1016/j.radonc.2013.10.022] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2013] [Revised: 10/11/2013] [Accepted: 10/19/2013] [Indexed: 11/28/2022]
|
35
|
Underwood TSA, Winter HC, Hill MA, Fenwick JD. Mass-density compensation can improve the performance of a range of different detectors under non-equilibrium conditions. Phys Med Biol 2013; 58:8295-310. [DOI: 10.1088/0031-9155/58/23/8295] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
|
36
|
A methodological approach to reporting corrected small field relative outputs. Radiother Oncol 2013; 109:350-5. [PMID: 24183867 DOI: 10.1016/j.radonc.2013.10.002] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2013] [Revised: 09/27/2013] [Accepted: 10/01/2013] [Indexed: 10/26/2022]
Abstract
PURPOSE The goal of this work was to set out a methodology for measuring and reporting small field relative output and to assess the application of published correction factors across a population of linear accelerators. METHODS AND MATERIALS Measurements were made at 6 MV on five Varian iX accelerators using two PTW T60017 unshielded diodes. Relative output readings and profile measurements were made for nominal square field sizes of side 0.5 to 1.0 cm. The actual in-plane (A) and cross-plane (B) field widths were taken to be the FWHM at the 50% isodose level. An effective field size, defined as √FS eff=A · B, was calculated and is presented as a field size metric. FSeff was used to linearly interpolate between published Monte Carlo (MC) calculated [Formula in text] values to correct for the diode over-response in small fields. RESULTS The relative output data reported as a function of the nominal field size were different across the accelerator population by up to nearly 10%. However, using the effective field size for reporting showed that the actual output ratios were consistent across the accelerator population to within the experimental uncertainty of ± 1.0%. Correcting the measured relative output using [Formula in text] at both the nominal and effective field sizes produce output factors that were not identical but differ by much less than the reported experimental and/or MC statistical uncertainties. CONCLUSIONS In general, the proposed methodology removes much of the ambiguity in reporting and interpreting small field dosimetric quantities and facilitates a clear dosimetric comparison across a population of linacs.
Collapse
|