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Perrett B, Seshadri V, Huxley C, Kumar S, Wawrzak M, Ramachandran P. Evaluation of radiation detectors for the determination of field output factors in Leksell Gamma Knife dosimetry using 3D printed phantom inserts. Phys Med 2024; 121:103370. [PMID: 38677196 DOI: 10.1016/j.ejmp.2024.103370] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/19/2023] [Revised: 02/22/2024] [Accepted: 04/22/2024] [Indexed: 04/29/2024] Open
Abstract
The Leksell Gamma Knife® Perfexion™ and Icon™ have a unique geometry, containing 192 60Co sources with collimation for field sizes of 4 mm, 8 mm, and 16 mm. 4 mm and 8 mm collimated fields lack lateral charged particle equilibrium, so accurate field output factors are essential. This study performs field output factor measurements for the microDiamond, microSilicon, and RAZOR™ Nano detectors. 3D printed inserts for the spherical Solid Water® Phantom were fabricated for microDiamond detector, the microSilicon unshielded diode and the RAZOR™ Nano micro-ionisation chamber. Detectors were moved iteratively to identify the peak detector signal for each collimator, representing the effective point of measurement of the chamber. In addition, field output correction factors were calculated for each detector relative to vendor supplied Monte Carlo simulated field output factors and field output factors measured with a W2 scintillator. All field output factors where within 1.1 % for the 4 mm collimator and within 2.3 % for the 8 mm collimator. The 3D printed phantom inserts were suitable for routine measurements if the user identifies the effective point of measurement, and ensures a reproducible setup by marking the rotational alignment of the cylindrical print. Measurements with the microDiamond and microSilicon can be performed faster compared to the RAZOR™ Nano due to differences in the signal to noise ratio. All detectors are suitable for field output factor measurements for the Leksell Gamma Knife® Perfexion™ and Icon™.
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Affiliation(s)
- Ben Perrett
- Radiation Oncology, Princess Alexandra Hospital, 199 Ipswich Road, Woolloongabba, Queensland 4102, Australia.
| | - Venkatakrishnan Seshadri
- Radiation Oncology, Princess Alexandra Hospital, 199 Ipswich Road, Woolloongabba, Queensland 4102, Australia
| | - Cosmo Huxley
- 3DOne Australia Pty Ltd, 30 Nashos Place, Wacol, Queensland 4102, Australia
| | - Sanjay Kumar
- Elekta Australia and New Zealand Pty Ltd, Suite 10.02, 146 Arthur Street, North Sydney, New South Wales 2060, Australia
| | - Michal Wawrzak
- Radiation Oncology, Princess Alexandra Hospital, 199 Ipswich Road, Woolloongabba, Queensland 4102, Australia
| | - Prabhakar Ramachandran
- Radiation Oncology, Princess Alexandra Hospital, 199 Ipswich Road, Woolloongabba, Queensland 4102, Australia
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Kim TH, Yang HJ, Jeong JY, Schaarschmidt T, Kim YK, Chung HT. Feasibility of Isodose-shaped scintillation detectors for the measurement of gamma Knife ® output factors. Med Phys 2022; 49:1944-1954. [PMID: 35050516 DOI: 10.1002/mp.15469] [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: 10/23/2021] [Revised: 12/20/2021] [Accepted: 01/06/2022] [Indexed: 11/07/2022] Open
Abstract
PURPOSE Scintillation detectors were 3D printed based on a gamma knife (GK) dose distribution to calculate the volume averaging effect. The collimator output factors were measured using isodose-shaped scintillators (ISSs) and compared with those of a micro-diamond detector and previous reports. METHODS An absorbed dose distribution in a spherical dosimetry phantom with a radius of 8 cm was obtained from GK treatment planning software (Leksell GammaPlan (LGP), Elekta AB, Stockholm, Sweden). Two types of ISSs were fabricated to fit the 97.2% (ISS-1) and 95.6% (ISS-2) isodose surfaces. The volume averaging correction factors were obtained by dividing the absorbed dose to water in the central voxel (CV) by that in the ISS. The correction effect due to the difference between the ISS and water was calculated by Monte Carlo simulations. Ten ISS detectors, five of each type, were used to measure the output factors of the 4 and 8 mm collimators of a GK IconTM to assess system consistency. The output factors of seven GKs were measured using two ISS detectors, one of each type, and a PTW T60019 (PTW, Freiburg, Germany) micro-diamond detector. RESULTS The detector output ratios (DORs) measured using the five ISSs of each type were consistent, with standard uncertainties less than 0.2%. In the 4 mm field, the volume averaging correction factor ratios were 1.018 and 1.026, and the output factors after all corrections were 0.827 (0.006) and 0.825 (0.006) for ISS-1 and ISS-2, respectively. In the 8 mm field, the volume averaging correction factor ratios were 1.000 for both ISS types, and the output factors were 0.898 (0.003) and 0.900 (0.003) for ISS-1 and ISS-2, respectively. The ISS detectors could measure the output factors of a GK with uncertainties comparable to that of the PTW 60019 detector. The output factors of all detectors decreased with the dose rate. CONCLUSION The volume averaging effect of an ISS developed in-house could be calculated using known dose distributions. The collimator output factors of the GK Perfexion/Icon™ models measured using ISS detectors were consistent with those of a commercial synthetic micro-diamond detector and recent studies. This article is protected by copyright. All rights reserved.
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Affiliation(s)
- Tae Hoon Kim
- Department of Nuclear Engineering, Hanyang University College of Engineering, Seoul, Republic of Korea
| | - Hye Jeong Yang
- Department of Biomedical Engineering, College of Medicine, Catholic University of Korea, Seoul, Republic of Korea
| | - Jae Young Jeong
- Department of Nuclear Engineering, Hanyang University College of Engineering, Seoul, Republic of Korea
| | - Thomas Schaarschmidt
- Department of Nuclear Engineering, Hanyang University College of Engineering, Seoul, Republic of Korea
| | - Yong Kyun Kim
- Department of Nuclear Engineering, Hanyang University College of Engineering, Seoul, Republic of Korea
| | - Hyun-Tai Chung
- Department of Neurosurgery, Seoul National University College of Medicine, Seoul, Republic of Korea
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Rudek B, Bernstein K, Osterman S, Qu T. Replacing gamma knife beam-profiles on film with point-detector scans. J Appl Clin Med Phys 2022; 23:e13522. [PMID: 35001499 DOI: 10.1002/acm2.13522] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2021] [Revised: 12/02/2021] [Accepted: 12/15/2021] [Indexed: 11/07/2022] Open
Abstract
PURPOSE Detector arrays and profile-scans have widely replaced film-measurements for quality assurance (QA) on linear accelerators. Film is still used for relative output factor (ROF) measurements, positioning, and dose-profile verification for annual Leksell Gamma Knife (LGK) QA. This study shows that small-field active detector measurements can be performed in the easily accessed clinical mode and that they are an effective replacement to time-consuming and exacting film measurements. METHODS Beam profiles and positioning scans for 4-mm, 8-mm, and 16-mm-collimated fields were collected along the x-, y-, and z-axes. The Exradin W2-scintillator and the PTW microdiamond-detector were placed in custom inserts centered in the Elekta solid-water phantom for these scans. GafChromic EBT3-film was irradiated with single uniformly collimated exposures as the clinical-standard reference, using the same solid-water phantom for profile tests and the Elekta film holder for radiation focal point (RFP)/patient-positioning system (PPS) coincidence. All experimental data were compared to the tissue-maximum-ratio-based (TMR10) dose calculation. RESULTS The detector-measured beam profiles and film-based profiles showed excellent agreement with TMR10-predicted full-width, half-maximum (FWHM) values. Absolute differences between the measured FWHM and FWHM from the treatment-planning system were on average 0.13 mm, 0.08 mm, and 0.04 mm for film, microdiamond, and scintillator, respectively. The coincidence between the RFP and the PPS was measured to be ≤0.5 mm with microdiamond, ≤0.41 mm with the W2-1 × 1 scintillator, and ≤0.22 mm using the film-technique. CONCLUSIONS Small-volume field detectors, used in conjunction with a clinically available phantom, an electrometer with data-logging, and treatment plans created in clinical mode offer an efficient and viable alternative for film-based profile tests. Position verification can be accurately performed when CBCT-imaging is available to correct for residual detector-position uncertainty. Scans are easily set up within the treatment-planning-system and, when coupled with an automated analysis, can provide accurate measurements within minutes.
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Affiliation(s)
- Benedikt Rudek
- Department of Radiation Oncology, Laura and Isaac Perlmutter Cancer Center, NYU Langone Health, New York, New York, USA
| | - Kenneth Bernstein
- Department of Radiation Oncology, Laura and Isaac Perlmutter Cancer Center, NYU Langone Health, New York, New York, USA
| | - Sunshine Osterman
- Department of Radiation Oncology, NYU Grossman School of Medicine, New York University, New York, New York, USA
| | - Tanxia Qu
- Department of Radiation Oncology, NYU Grossman School of Medicine, New York University, New York, New York, USA
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Petti PL, Rivard MJ, Alvarez PE, Bednarz G, Daniel Bourland J, DeWerd LA, Drzymala RE, Johansson J, Kunugi K, Ma L, Meltsner SG, Neyman G, Seuntjens JP, Shiu AS, Goetsch SJ. Recommendations on the practice of calibration, dosimetry, and quality assurance for gamma stereotactic radiosurgery: Report of AAPM Task Group 178. Med Phys 2021; 48:e733-e770. [DOI: 10.1002/mp.14831] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2020] [Revised: 02/21/2021] [Accepted: 02/24/2021] [Indexed: 12/25/2022] Open
Affiliation(s)
- Paula L. Petti
- Gamma Knife Center Washington Hospital Fremont CA 94538 USA
| | - Mark J. Rivard
- Department of Radiation Oncology Alpert Medical School of Brown University Providence RI 02903 USA
| | - Paola E. Alvarez
- Radiological Physics Center University of Texas MD Anderson Cancer Center Houston TX 77054 USA
| | - Greg Bednarz
- Department of Radiation Oncology University of Pittsburgh Medical Center Pittsburgh PA 15232 USA
| | - J. Daniel Bourland
- Department of Radiation Oncology Wake Forest University Winston‐Salem NC 27157 USA
| | - Larry A. DeWerd
- Accredited Dosimetry and Calibration Laboratory University of Wisconsin Madison WI 53705 USA
| | - Robert E. Drzymala
- Department of Radiation Oncology Washington University Saint Louis MO 63119 USA
| | | | - Keith Kunugi
- Accredited Dosimetry and Calibration Laboratory University of Wisconsin Madison WI 53705 USA
| | - Lijun Ma
- Department of Radiation Oncology University California–San Francisco San Francisco CA 94143 USA
| | - Sheridan G. Meltsner
- Department of Radiation Oncology Duke University Medical Center Durham NC 27713 USA
| | - Gennady Neyman
- Department of Radiation Oncology The Cleveland Clinic Cleveland OH 44195 USA
| | - Jan P. Seuntjens
- Department of Medical Physics McGill University Montreal QC H4A3J1 Canada
| | - Almon S. Shiu
- Department of Radiation Oncology University of Southern California Los Angeles CA 90033 USA
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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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Häger W, Kaveckyte V, Benmakhlouf H. Experimental investigation of TRS-483 reference dosimetry correction factors for Leksell Gamma Knife® Icon™ beams. Med Phys 2020; 48:434-444. [PMID: 33119131 PMCID: PMC7894485 DOI: 10.1002/mp.14561] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2020] [Revised: 09/22/2020] [Accepted: 09/29/2020] [Indexed: 11/28/2022] Open
Abstract
Purpose Radiosurgery using the Leksell Gamma Knife® (LGK) Icon™ is an established technique used for treating intracranial lesions. The largest beam field size the LGK Icon can produce is a 16 mm diameter sphere. Despite this, reference dosimetry on the LGK Icon is typically performed using ionization chambers calibrated in 10 × 10 cm2 fields. Furthermore, plastic phantoms are widely used instead of liquid water phantoms. In an effort to resolve these issues, the International Atomic Energy Agency (IAEA) in collaboration with American Association of Physicists in medicine (AAPM) recently published Technical Report Series No. 483 (TRS‐483) as a Code of Practice for small‐field dosimetry. TRS‐483 includes small‐field correction factors, kQmsr,Q0fmsr,fref, intended to account for the differences between setups when using small‐field modalities such as the LGK Icon, and conventional setups. Since the publication of TRS‐483, at least three new sets of values of kQmsr,Q0fmsr,fref for the LGK Icon have been published. The purpose of this study was to experimentally investigate the published values of kQmsr,Q0fmsr,fref for commonly used phantom and ionization chamber (IC) models for the LGK Icon. Methods Dose‐rates from two LGK units were determined using acrylonitrile butadiene styrene (ABS) and Certified Medical Grade Solid Water® (SW) phantoms, and PTW 31010 and PTW 31016 ICs. Correction factors were applied, and the resulting dose‐rates compared. Relative validity of the correction factors was investigated by taking the ratios of dose‐rate correction factor products. Additionally, dose‐rates from the individual sectors were determined in order to calculate the beam attenuation caused by the ABS phantom adapter. Results and Conclusions It was seen that the dose‐rate is underestimated by at least 1% when using the ABS phantom, which was attributed to fluence perturbation caused by the IC and phantom adapter. Published correction factors kQmsr,Q0fmsr,fref account for these effects to varying degree and should be used. The SW phantom is unlikely to underestimate the dose‐rate by more than 1%, and applying kQmsr,Q0fmsr,fref could not be shown to be necessary. Out of the two phantom models, the ABS phantom is not recommended for use in LGK reference dosimetry. The use of newly published values of kQmsr,Q0fmsr,fref should be considered.
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Affiliation(s)
- Wille Häger
- Department of Physics, Stockholm University, Stockholm, SE-106 91, Sweden
| | - Vaiva Kaveckyte
- Radiation Physics, Department of Medical and Health Sciences, Linköping University, Linköping, SE-581 85, Sweden.,Department of Medical Radiation Physics and Nuclear Medicine, Karolinska University Hospital, Stockholm, SE-171 76, Sweden
| | - Hamza Benmakhlouf
- Department of Medical Radiation Physics and Nuclear Medicine, Karolinska University Hospital, Stockholm, SE-171 76, Sweden
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Costa NA, Patallo IS, Dimitriadis A, Saraiva CW, Potiens MDPA. Phantom development and implementation for Gamma Knife® dosimetry. Radiat Phys Chem Oxf Engl 1993 2020. [DOI: 10.1016/j.radphyschem.2019.108355] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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Kry SF, Alvarez P, Cygler JE, DeWerd LA, Howell RM, Meeks S, O'Daniel J, Reft C, Sawakuchi G, Yukihara EG, Mihailidis D. AAPM TG 191: Clinical use of luminescent dosimeters: TLDs and OSLDs. Med Phys 2019; 47:e19-e51. [DOI: 10.1002/mp.13839] [Citation(s) in RCA: 62] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2019] [Revised: 08/27/2019] [Accepted: 08/28/2019] [Indexed: 12/20/2022] Open
Affiliation(s)
- Stephen F. Kry
- The University of Texas MD Anderson Cancer Center Houston TX USA
| | - Paola Alvarez
- The University of Texas MD Anderson Cancer Center Houston TX USA
| | | | | | | | - Sanford Meeks
- University of Florida Health Cancer Center Orlando FL USA
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Therriault-Proulx F, Pino R, Yang JN, Beddar AS. Quality assurance for Gamma Knife Perfexion using the Exradin W1 plastic scintillation detector and Lucy phantom. Phys Med Biol 2019; 64:225007. [PMID: 31581139 DOI: 10.1088/1361-6560/ab4ac3] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The goal of this work is to validate the use of the Exradin W1 plastic scintillation detector (PSD) to measure profiles and output factors from Gamma Knife Perfexion collimators in a Lucy phantom. The Exradin W1 PSD has a small-volume, near-water-equivalent, energy-independent sensitive element. Output measurements were performed for all 3 collimators (4 mm, 8 mm, and 16 mm) of the Gamma Knife Perfexion system, and these measurements were compared to measurements made with an A16 ion chamber and an EBT3 film and to the nominal values. We showed that a configuration in which the focus or 'shot' moves while the detector remains fixed is essentially equivalent to a configuration in which the focus is fixed while the detector moves. A Lucy phantom containing a PSD was moved in small steps to acquire profiles in all three dimensions. EBT3 film was inserted in the Lucy phantom and exposed to a single shot for each collimator. The relative values for output factors measured with the PSD were 1.000, 0.892, and 0.795, for the 16 mm, 8 mm, and 4 mm collimators, respectively. The values measured with EBT3 film were 1.000, 0.881, and 0.793, and the values measured with the A16 ion chamber were 1.000, 0.883, and 0.727. The nominal output factors for the Gamma Knife Perfexion are 1.000, 0.900, and 0.814, respectively. There was excellent agreement between all profiles measured with the PSD and EBT3 as well as with the treatment planning system data provided by the vendor. In light of our results, the Exradin W1 PSD is well suited for beam quality assurance of a Gamma Knife Perfexion irradiator.
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Affiliation(s)
- Francois Therriault-Proulx
- Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, United States of America
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Kim TH, Schaarschmidt T, Yang HJ, Kim YK, Chun KJ, Choi Y, Chung HT. Development of an IAEA phase-space dataset for the Leksell Gamma Knife® Perfexion™ using multi-threaded Geant4 simulations. Phys Med 2019; 64:222-229. [DOI: 10.1016/j.ejmp.2019.07.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/19/2019] [Revised: 06/07/2019] [Accepted: 07/01/2019] [Indexed: 10/26/2022] Open
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Akino Y, Mizuno H, Tanaka Y, Isono M, Masai N, Yamamoto T. Inter-institutional variability of small-field-dosimetry beams among HD120™ multileaf collimators: a multi-institutional analysis. ACTA ACUST UNITED AC 2018; 63:205018. [DOI: 10.1088/1361-6560/aae450] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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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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Chung JP, Seong YM, Kim TY, Choi Y, Kim TH, Choi HJ, Min CH, Benmakhlouf H, Chun KJ, Chung HT. Development of a PMMA phantom as a practical alternative for quality control of gamma knife® dosimetry. Radiat Oncol 2018; 13:176. [PMID: 30217160 PMCID: PMC6137750 DOI: 10.1186/s13014-018-1117-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2018] [Accepted: 08/27/2018] [Indexed: 11/17/2022] Open
Abstract
BACKGROUND To measure the absorbed dose rate to water and penumbra of a Gamma Knife® (GK) using a polymethyl metacrylate (PMMA) phantom. METHODS A multi-purpose PMMA phantom was developed to measure the absorbed dose rate to water and the dose distribution of a GK. The phantom consists of a hemispherical outer phantom, one exchangeable cylindrical chamber-hosting inner phantom, and two film-hosting inner phantoms. The radius of the phantom was determined considering the electron density of the PMMA such that it corresponds to 8 g/cm2 water depth, which is the reference depth of the absorbed dose measurement of GK. The absorbed dose rate to water was measured with a PTW TN31010 chamber, and the dose distributions were measured with radiochromic films at the calibration center of a patient positioning system of a GK Perfexion. A spherical water-filled phantom with the same water equivalent depth was constructed as a reference phantom. The dose rate to water and dose distributions at the center of a circular field delimited by a 16-mm collimator were measured with the PMMA phantom at six GK Perfexion sites. RESULTS The radius of the PMMA phantom was determined to be 6.93 cm, corresponding to equivalent water depth of 8 g/cm2. The absorbed dose rate to water was measured with the PMMA phantom, the spherical water-filled phantom and a commercial solid water phantom. The measured dose rate with the PMMA phantom was 1.2% and 1.8% higher than those measured with the spherical water-filled phantom and the solid water phantom, respectively. These differences can be explained by the scattered photon contribution of PMMA off incoming 60Co gamma-rays to the dose rate. The average full width half maximum and penumbra values measured with the PMMA phantom showed reasonable agreement with two calculated values, one at the center of the PMMA phantom (LGP6.93) and other at the center of a water sphere with a radius of 8 cm (LGP8.0) given by Leksell Gamma Plan using the TMR10 algorithm. CONCLUSIONS A PMMA phantom constructed in this study to measure the absorbed dose rates to water and dose distributions of a GK represents an acceptable and practical alternative for GK dosimetry considering its cost-effectiveness and ease of handling.
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Affiliation(s)
- Jae Pil Chung
- Center for Ionizing Radiation, Division of Metrology for Quality of Life, Korea Research Institute of Standards and Science, 267 Gajeong-ro, Yuseong-gu, Daejon, 34311 Korea
| | - Young Min Seong
- Center for Ionizing Radiation, Division of Metrology for Quality of Life, Korea Research Institute of Standards and Science, 267 Gajeong-ro, Yuseong-gu, Daejon, 34311 Korea
| | - Tae Yeon Kim
- Department of Accelerator Science, Korea University Sejong Campus, 2511 Sejong-ro, Sejong, 30019 Korea
| | - Yona Choi
- Department of Accelerator Science, Korea University Sejong Campus, 2511 Sejong-ro, Sejong, 30019 Korea
| | - Tae Hoon Kim
- Department of Nuclear Engineering, Hanyang University College of Engineering, Seoul, 04763 Korea
| | - Hyun Joon Choi
- Department of Radiation Convergence Engineering, Yonsei University, 1 Yeonsedae-gil, Heungeop-myeon, Wonju, 26493 Korea
| | - Chul Hee Min
- Department of Radiation Convergence Engineering, Yonsei University, 1 Yeonsedae-gil, Heungeop-myeon, Wonju, 26493 Korea
| | - Hamza Benmakhlouf
- Department of Medical Radiation Physics and Nuclear Medicine, Karolinska University Hospital, SE-17176 Stockholm, Sweden
| | - Kook Jin Chun
- Department of Accelerator Science, Korea University Sejong Campus, 2511 Sejong-ro, Sejong, 30019 Korea
| | - Hyun-Tai Chung
- Department of Neurosurgery, Seoul National University College of Medicine, 101 Daehak-ro Jongno-gu, Seoul, 03080 Korea
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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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Parwaie W, Refahi S, Ardekani MA, Farhood B. Different Dosimeters/Detectors Used in Small-Field Dosimetry: Pros and Cons. JOURNAL OF MEDICAL SIGNALS & SENSORS 2018; 8:195-203. [PMID: 30181968 PMCID: PMC6116321 DOI: 10.4103/jmss.jmss_3_18] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
With the advent of complex and precise radiation therapy techniques, the use of relatively small fields is needed. Using such field sizes can cause uncertainty in dosimetry; therefore, special attention is required both in dose calculations and measurements. There are several challenges in small-field dosimetry such as the steep gradient of the radiation field, volume averaging effect, lack of charged particle equilibrium, partial occlusion of radiation source, beam alignment, and unable to use a reference dosimeter. Due to these challenges, special dosimeters are needed for small-field dosimetry, and this review article discusses this topic.
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Affiliation(s)
- Wrya Parwaie
- Department of Medical Physics and Biomedical Engineering, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran
| | - Soheila Refahi
- Department of Medical Physics, Faculty of Medicine, Ardabil University of Medical Sciences, Ardabil, Iran
| | - Mahdieh Afkhami Ardekani
- Department of Radiology, Faculty of Para-Medicine, Hormozgan University of Medical Sciences, Bandar Abbas, Iran
| | - Bagher Farhood
- Department of Radiology and Medical Physics, Faculty of Paramedical Sciences, Kashan University of Medical Sciences, Kashan, Iran
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16
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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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17
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Veselsky T, Novotny J, Pastykova V, Koniarova I. Determination of small field synthetic single-crystal diamond detector correction factors for CyberKnife, Leksell Gamma Knife Perfexion and linear accelerator. Phys Med 2017; 44:66-71. [DOI: 10.1016/j.ejmp.2017.11.010] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/22/2017] [Revised: 10/09/2017] [Accepted: 11/09/2017] [Indexed: 10/18/2022] Open
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18
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Kaveckyte V, Malusek A, Benmakhlouf H, Alm Carlsson G, Carlsson Tedgren Å. Suitability of microDiamond detectors for the determination of absorbed dose to water around high-dose-rate 192 Ir brachytherapy sources. Med Phys 2017; 45:429-437. [PMID: 29171060 DOI: 10.1002/mp.12694] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2017] [Revised: 10/26/2017] [Accepted: 10/29/2017] [Indexed: 11/06/2022] Open
Abstract
PURPOSE Experimental dosimetry of high-dose-rate (HDR) 192 Ir brachytherapy (BT) sources is complicated due to high dose and dose-rate gradients, and softening of photon energy spectrum with depth. A single crystal synthetic diamond detector microDiamond (PTW 60019, Freiburg, Germany) has a small active volume, high sensitivity, direct readout, and nearly water-equivalent active volume. The purpose of this study was to evaluate the suitability of microDiamond detectors for the determination of absorbed dose to water around HDR 192 Ir BT sources. Three microDiamond detectors were used, allowing for the comparison of their properties. METHODS In-phantom measurements were performed using microSelectron and VariSource iX HDR 192 Ir BT treatment units. Their treatment planning systems (TPSs), Oncentra (v. 4.3) and BrachyVision (v. 13.6), respectively, were used to create irradiation plans for a cubic PMMA phantom with the microDiamond positioned at one of three source-to-detector distances (SDDs) (1.5, 2.5, and 5.5 cm) at a time. The source was stepped in increments of 0.5 cm over a total length of 6 cm to yield absorbed dose of 2 Gy at the nominal reference-point of the detector. Detectors were calibrated in 60 Co beam in terms of absorbed dose to water, and Monte Carlo (MC) calculated beam quality correction factors were applied to account for absorbed-dose energy dependence. Phantom correction factors were applied to account for differences in dimensions between the measurement phantom and a water phantom used for absorbed dose calculations made with a TPS. The same measurements were made with all three of the detectors. Additionally, dose-rate dependence and stability of the detectors were evaluated in 60 Co beam. RESULTS The percentage differences between experimentally determined and TPS-calculated absorbed doses to water were from -1.3% to +2.9%. The values agreed to within experimental uncertainties, which were from 1.9% to 4.3% (k = 2) depending on the detector, SDD and treatment delivery unit. No dose-rate or intrinsic energy dependence corrections were applied. All microDiamonds were comparable in terms of preirradiation dose, stability of the readings and energy response, and showed a good agreement. CONCLUSIONS The results indicate that the microDiamond is potentially suitable for the determination of absorbed dose to water around HDR 192 Ir BT sources and may be used for independent verification of TPS's calculations, as well as for QA measurements of HDR 192 Ir BT treatment delivery units at clinical sites.
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Affiliation(s)
- Vaiva Kaveckyte
- Radiation Physics, Department of Medical and Health Sciences, Linköping University, SE-581 85, Linköping, Sweden
| | - Alexandr Malusek
- Radiation Physics, Department of Medical and Health Sciences, Linköping University, SE-581 85, Linköping, Sweden
| | - Hamza Benmakhlouf
- Department of Medical Radiation Physics and Nuclear Medicine, Karolinska University Hospital, SE-171 76, Stockholm, Sweden
| | - Gudrun Alm Carlsson
- Radiation Physics, Department of Medical and Health Sciences, Linköping University, SE-581 85, Linköping, Sweden
| | - Åsa Carlsson Tedgren
- Radiation Physics, Department of Medical and Health Sciences, Linköping University, SE-581 85, Linköping, Sweden.,Department of Medical Radiation Physics and Nuclear Medicine, Karolinska University Hospital, SE-171 76, Stockholm, Sweden
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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.
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Affiliation(s)
- E Zoros
- Medical Physics Laboratory, Medical School, National and Kapodistrian University of Athens, 75 Mikras Asias, 115 27 Athens, Greece
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20
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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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21
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Chung HT, Park JH, Chun KJ. Verification of dose profiles generated by the convolution algorithm of the gamma knife ® radiosurgery planning system. Med Phys 2017; 44:4880-4889. [PMID: 28513854 DOI: 10.1002/mp.12347] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2016] [Revised: 05/08/2017] [Accepted: 05/11/2017] [Indexed: 11/09/2022] Open
Abstract
PURPOSE A convolution algorithm that takes into account electron-density inhomogeneity was recently introduced to calculate dose distributions for the Gamma Knife (GK) Perfexion™ treatment planning program. The accuracies of the dose distributions computed using the convolution method were assessed using an anthropomorphic phantom and film dosimetry. METHODS Absorbed-dose distributions inside a phantom (CIRS Radiosurgery Head Phantom, Model 605) were calculated using the convolution method of the GK treatment-planning software (Leksell Gamma Plan® version 10.1; LGP) for various combinations of collimator size, location, direction of calculation plane, and number of shots. Computed tomography (CT) images of the phantom and a data set of CT number versus electron density were provided to the LGP. Calculated distributions were exported as digital-image communications in medicine-radiation therapy (DICOM-RT) files. Three types of radiochromic film (GafChromic® MD-V2-55, MD-V3, and EBT2) were irradiated inside the phantom using GK Perfexion™. Scanned images of the measured films were processed following standard radiochromic film-handling procedures. For a two-dimensional quantitative evaluation, gamma index pass rates (GIPRs) and normalized agreement-test indices (NATIs) were obtained. Image handling and index calculations were performed using a commercial software package (DoseLab Pro version 6.80). RESULTS The film-dose calibration data were well fitted with third-order polynomials (R2 ≥ 0.9993). The mean GIPR and NATI of the 93 analyzed films were 99.3 ± 1.1% and 0.8 ± 1.3, respectively, using 3%/1.0 mm criteria. The calculated maximum doses were 4.3 ± 1.7% higher than the measured values for the 4 mm single shots and 1.8 ± 0.7% greater than those for the 8 mm single shots, whereas differences of only 0.3 ± 0.9% were observed for the 16 mm single shots. The accuracy of the calculated distribution was not statistically related to the collimator size, number of shots, or centrality of location (P > 0.05, independent-sample t-test). The plans in the axial planes exhibited poorer agreement with the measured distributions than the plans in the coronal or sagittal planes; however, their GIPR values (≥ 96.9%) were clinically acceptable. The plans for an arbitrary virtual target of volume 1.6 cm3 at an axial plane close to the top of the phantom showed the worst agreement and the greatest fluctuation (GIPR = 96.9 ± 1.2%, NATI = 3.9 ± 1.7). CONCLUSIONS The measured accuracies of the dose distributions calculated by the convolution algorithm of the LGP were within the clinically acceptable range (GIPR ≥ 96.9%) for various configurations of collimator size, location, direction of calculation plane, and number of shots. Due to the intrinsic asymmetry in the dose distribution along the z-axis, the treatment plan should also be verified in coronal or sagittal plane.
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Affiliation(s)
- Hyun-Tai Chung
- Department of Neurosurgery, College of Medicine, Seoul National University College of Medicine, Seoul, 03080, Korea
| | - Jeong-Hoon Park
- Department of Radiation Oncology, Baylor Scott & White Health, Temple, TX, 76508, USA
| | - Kook Jin Chun
- Department of Accelerator Science, Korea University Sejong Campus, 2511 Sejong-ro, Sejong, 30019, Korea
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22
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Sahgal A, Ruschin M, Ma L, Verbakel W, Larson D, Brown PD. Stereotactic radiosurgery alone for multiple brain metastases? A review of clinical and technical issues. Neuro Oncol 2017; 19:ii2-ii15. [PMID: 28380635 DOI: 10.1093/neuonc/nox001] [Citation(s) in RCA: 65] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Over the past three decades several randomized trials have enabled evidence-based practice for patients presenting with limited brain metastases. These trials have focused on the role of surgery or stereotactic radiosurgery (SRS) with or without whole brain radiation therapy (WBRT). As a result, it is clear that local control should be optimized with surgery or SRS in patients with optimal prognostic factors presenting with up to 4 brain metastases. The routine use of adjuvant WBRT remains debatable, as although greater distant brain control rates are observed, there is no impact on survival, and modern outcomes suggest adverse effects from WBRT on patient cognition and quality of life. With dramatic technologic advances in radiation oncology facilitating the adoption of SRS into mainstream practice, the optimal management of patients with multiple brain metastases is now being put forward. Practice is evolving to SRS alone in these patients despite a lack of level 1 evidence to support a clinical departure from WBRT. The purpose of this review is to summarize the current state of the evidence for patients presenting with limited and multiple metastases, and to present an in-depth analysis of the technology and dosimetric issues specific to the treatment of multiple metastases.
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Affiliation(s)
- Arjun Sahgal
- Department of Radiation Oncology, Sunnybrook Odette Cancer Centre, University of Toronto, Toronto, Ontario, Canada
| | - Mark Ruschin
- Department of Radiation Oncology, Sunnybrook Odette Cancer Centre, University of Toronto, Toronto, Ontario, Canada
| | - Lijun Ma
- Department of Radiation Oncology, University of California San Francisco, San Francisco, California, USA
| | - Wilko Verbakel
- Department of Radiation Oncology, VU University Medical Center, Amsterdam,The Netherlands
| | - David Larson
- Department of Radiation Oncology, University of California San Francisco, San Francisco, California, USA
| | - Paul D Brown
- Department of Radiation Oncology, Mayo Clinic, Rochester, Minnesota, USA
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23
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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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24
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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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25
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Rossomme S, Denis JM, Souris K, Delor A, Bartier F, Dumont D, Vynckier S, Palmans H. LET dependence of the response of a PTW-60019 microDiamond detector in a 62MeV proton beam. Phys Med 2016; 32:1135-8. [PMID: 27567088 DOI: 10.1016/j.ejmp.2016.08.017] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/11/2016] [Revised: 08/17/2016] [Accepted: 08/20/2016] [Indexed: 10/21/2022] Open
Abstract
This study was initiated following conclusions from earlier experimental work, performed in a low-energy carbon ion beam, indicating a significant LET dependence of the response of a PTW-60019 microDiamond detector. The purpose of this paper is to present a comparison between the response of the same PTW-60019 microDiamond detector and an IBA Roos-type ionization chamber as a function of depth in a 62MeV proton beam. Even though proton beams are considered as low linear energy transfer (LET) beams, the LET value increases slightly in the Bragg peak region. Contrary to the observations made in the carbon ion beam, in the 62MeV proton beam good agreement is found between both detectors in both the plateau and the distal edge region. No significant LET dependent response of the PTW-60019 microDiamond detector is observed consistent with other findings for proton beams in the literature, despite this particular detector exhibiting a substantial LET dependence in a carbon ion beam.
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Affiliation(s)
- S Rossomme
- Center of Molecular Imaging, Radiotherapy and Oncology, Institut de Recherche Expérimentale et Clinique, Université catholique de Louvain, B-1200 Brussels, Belgium.
| | - J M Denis
- Cliniques Universitaires Saint-Luc, Radiotherapy and Oncology Department, B-1200 Brussels, Belgium
| | - K Souris
- Center of Molecular Imaging, Radiotherapy and Oncology, Institut de Recherche Expérimentale et Clinique, Université catholique de Louvain, B-1200 Brussels, Belgium
| | - A Delor
- Cliniques Universitaires Saint-Luc, Radiotherapy and Oncology Department, B-1200 Brussels, Belgium
| | - F Bartier
- Cliniques Universitaires Saint-Luc, Radiotherapy and Oncology Department, B-1200 Brussels, Belgium
| | - D Dumont
- Cliniques Universitaires Saint-Luc, Radiotherapy and Oncology Department, B-1200 Brussels, Belgium
| | - S Vynckier
- Center of Molecular Imaging, Radiotherapy and Oncology, Institut de Recherche Expérimentale et Clinique, Université catholique de Louvain, B-1200 Brussels, Belgium; Cliniques Universitaires Saint-Luc, Radiotherapy and Oncology Department, B-1200 Brussels, Belgium
| | - H Palmans
- EBG MedAustron GmbH, A-2700 Wiener Neustadt, Austria; National Physical Laboratory, Acoustics and Ionising Radiation Division, Teddington TW11 0LW, United Kingdom
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26
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Bouchard H, Kamio Y, Palmans H, Seuntjens J, Duane S. Detector dose response in megavoltage small photon beams. II. Pencil beam perturbation effects. Med Phys 2016; 42:6048-61. [PMID: 26429280 DOI: 10.1118/1.4930798] [Citation(s) in RCA: 49] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE To quantify detector perturbation effects in megavoltage small photon fields and support the theoretical explanation on the nature of quality correction factors in these conditions. METHODS In this second paper, a modern approach to radiation dosimetry is defined for any detector and applied to small photon fields. Fano's theorem is adapted in the form of a cavity theory and applied in the context of nonstandard beams to express four main effects in the form of perturbation factors. The pencil-beam decomposition method is detailed and adapted to the calculation of perturbation factors and quality correction factors. The approach defines a perturbation function which, for a given field size or beam modulation, entirely determines these dosimetric factors. Monte Carlo calculations are performed in different cavity sizes for different detection materials, electron densities, and extracameral components. RESULTS Perturbation effects are detailed with calculated perturbation functions, showing the relative magnitude of the effects as well as the geometrical extent to which collimating or modulating the beam impacts the dosimetric factors. The existence of a perturbation zone around the detector cavity is demonstrated and the approach is discussed and linked to previous approaches in the literature to determine critical field sizes. CONCLUSIONS Monte Carlo simulations are valuable to describe pencil beam perturbation effects and detail the nature of dosimetric factors in megavoltage small photon fields. In practice, it is shown that dosimetric factors could be avoided if the field size remains larger than the detector perturbation zone. However, given a detector and beam quality, a full account for the detector geometry is necessary to determine critical field sizes.
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Affiliation(s)
- Hugo Bouchard
- Acoustics and Ionising Radiation Team, National Physical Laboratory, Hampton Road, Teddington TW11 0LW, United Kingdom
| | - Yuji Kamio
- Centre hospitalier de l'Université de Montréal (CHUM), 1560 Sherbrooke Est, Montréal, Québec H2L 4M1, Canada
| | - Hugo Palmans
- Acoustics and Ionising Radiation Team, National Physical Laboratory, Hampton Road, Teddington TW11 0LW, United KingdomMedical Physics, EBG MedAustron GmbH, Wiener Neustadt A-2700, Austria
| | - Jan Seuntjens
- Medical Physics Unit, McGill University, Montréal, Québec H3G 1A4, Canada
| | - Simon Duane
- Acoustics and Ionising Radiation Team, National Physical Laboratory, Hampton Road, Teddington TW11 0LW, United Kingdom
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Cheng JY, Ning H, Arora BC, Zhuge Y, Miller RW. Output factor comparison of Monte Carlo and measurement for Varian TrueBeam 6 MV and 10 MV flattening filter-free stereotactic radiosurgery system. J Appl Clin Med Phys 2016; 17:100-110. [PMID: 27167266 PMCID: PMC5690931 DOI: 10.1120/jacmp.v17i3.5956] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2015] [Revised: 12/30/2015] [Accepted: 12/22/2015] [Indexed: 11/25/2022] Open
Abstract
The dose measurements of the small field sizes, such as conical collimators used in stereotactic radiosurgery (SRS), are a significant challenge due to many factors including source occlusion, detector size limitation, and lack of lateral electronic equilibrium. One useful tool in dealing with the small field effect is Monte Carlo (MC) simulation. In this study, we report a comparison of Monte Carlo simulations and measurements of output factors for the Varian SRS system with conical collimators for energies of 6 MV flattening filter‐free (6 MV) and 10 MV flattening filter‐free (10 MV) on the TrueBeam accelerator. Monte Carlo simulations of Varian's SRS system for 6 MV and 10 MV photon energies with cones sizes of 17.5 mm, 15.0 mm, 12.5 mm, 10.0 mm, 7.5 mm, 5.0 mm, and 4.0 mm were performed using EGSnrc (release V4 2.4.0) codes. Varian's version‐2 phase‐space files for 6 MV and 10 MV of TrueBeam accelerator were utilized in the Monte Carlo simulations. Two small diode detectors Edge (Sun Nuclear) and Small Field Detector (SFD) (IBA Dosimetry) were applied to measure the output factors. Significant errors may result if detector correction factors are not applied to small field dosimetric measurements. Although it lacked the machine‐specific kQclin,Qmsrfclin,fmsr correction factors for diode detectors in this study, correction factors were applied utilizing published studies conducted under similar conditions. For cone diameters greater than or equal to 12.5 mm, the differences between output factors for the Edge detector, SFD detector, and MC simulations are within 3.0% for both energies. For cone diameters below 12.5 mm, output factors differences exhibit greater variations. PACS number(s): 87.55.k, 87.55.Qr
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Affiliation(s)
- Jason Y Cheng
- National Cancer Institute; National Institutes of Health.
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Pappas EP, Moutsatsos A, Pantelis E, Zoros E, Georgiou E, Torrens M, Karaiskos P. On the development of a comprehensive MC simulation model for the Gamma Knife Perfexion radiosurgery unit. Phys Med Biol 2016; 61:1182-203. [PMID: 26788618 DOI: 10.1088/0031-9155/61/3/1182] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
This work presents a comprehensive Monte Carlo (MC) simulation model for the Gamma Knife Perfexion (PFX) radiosurgery unit. Model-based dosimetry calculations were benchmarked in terms of relative dose profiles (RDPs) and output factors (OFs), against corresponding EBT2 measurements. To reduce the rather prolonged computational time associated with the comprehensive PFX model MC simulations, two approximations were explored and evaluated on the grounds of dosimetric accuracy. The first consists in directional biasing of the (60)Co photon emission while the second refers to the implementation of simplified source geometric models. The effect of the dose scoring volume dimensions in OF calculations accuracy was also explored. RDP calculations for the comprehensive PFX model were found to be in agreement with corresponding EBT2 measurements. Output factors of 0.819 ± 0.004 and 0.8941 ± 0.0013 were calculated for the 4 mm and 8 mm collimator, respectively, which agree, within uncertainties, with corresponding EBT2 measurements and published experimental data. Volume averaging was found to affect OF results by more than 0.3% for scoring volume radii greater than 0.5 mm and 1.4 mm for the 4 mm and 8 mm collimators, respectively. Directional biasing of photon emission resulted in a time efficiency gain factor of up to 210 with respect to the isotropic photon emission. Although no considerable effect on relative dose profiles was detected, directional biasing led to OF overestimations which were more pronounced for the 4 mm collimator and increased with decreasing emission cone half-angle, reaching up to 6% for a 5° angle. Implementation of simplified source models revealed that omitting the sources' stainless steel capsule significantly affects both OF results and relative dose profiles, while the aluminum-based bushing did not exhibit considerable dosimetric effect. In conclusion, the results of this work suggest that any PFX simulation model should be benchmarked in terms of both RDP and OF results.
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Affiliation(s)
- E P Pappas
- Medical Physics Laboratory, Medical School, National and Kapodistrian University of Athens, 75 Mikras Asias, 115 27 Athens, Greece
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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]
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30
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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
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