1
|
Yip E, Tari SY, Reynolds MW, Sinn D, Murray BR, Fallone BG, Oliver PA. Clinical reference dosimetry for the 0.5 T inline rotating biplanar Linac-MR. Med Phys 2024; 51:2933-2940. [PMID: 38308821 DOI: 10.1002/mp.16951] [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: 08/09/2023] [Revised: 11/13/2023] [Accepted: 12/26/2023] [Indexed: 02/05/2024] Open
Abstract
BACKGROUND The world's first clinical 0.5 T inline rotating biplanar Linac-MR system is commissioned for clinical use. For reference dosimetry, unique features to device, including an SAD = 120 cm, bore clearance of 60 cm × 110 cm, as well as 0.5 T inline magnetic field, provide some challenges to applying a standard dosimetry protocol (i.e., TG-51). PURPOSE In this work, we propose a simple and practical clinical reference dosimetry protocol for the 0.5T biplanar Linac-MR and validated its results. METHODS Our dosimetry protocol for this system is as follows: tissue phantom ratios at 20 and 10 cm are first measured and converted into %dd10x beam quality specifier using equations provided and Kalach and Rogers. The converted %dd10x is used to determine the ion chamber correction factor, using the equations in the TG-51 addendum for the Exradin A12 farmer chamber used, which is cross-calibrated with one calibrated at a standards laboratory. For a 0.5 T parallel field, magnetic field effect on chamber response is assumed to have no effect and is not explicitly corrected for. Once the ion chamber correction factor for a non-standard SAD (kQ,msr) is determined, TG-51 is performed to obtain dose at a depth of 10 cm at SAD = 120 cm. The dosimetry protocol is repeated with the magnetic field ramped down. To validate our dosimetry protocol, Monte Carlo (EGSnrc) simulations are performed to confirm the determined kQ,msr values. MC Simulations and magnetic Field On versus Field Off measurements are performed to confirm that the magnetic field has no effect. To validate our overall dosimetry protocol, external dose audits, based on optical simulated luminescent dosimeters, thermal luminescent dosimeters, and alanine dosimeters are performed on the 0.5 T Linac-MR system. RESULTS Our EGSnrc results confirm our protocol-determined kQ,msr values, as well as our assumptions about magnetic field effects (kB = 1) within statistical uncertainty for the A-12 chamber. Our external dosimetry procedures also validated our overall dosimetry protocol for the 0.5 T biplanar Linac-MR hybrid. Ramping down the magnetic field has resulted in a dosimetric difference of 0.1%, well within experimental uncertainty. CONCLUSION With the 0.5 T parallel magnetic field having minimal effect on the ion chamber response, a TPR20,10 approach to determine beam quality provides an accurate method to perform clinical dosimetry for the 0.5 T biplanar Linac-MR.
Collapse
Affiliation(s)
- Eugene Yip
- Department of Oncology, Medical Physics Division, University of Alberta, Edmonton, Alberta, Canada
- Department of Medical Physics, Cross Cancer Institute, Edmonton, Alberta, Canada
| | - Shima Y Tari
- Department of Oncology, Medical Physics Division, University of Alberta, Edmonton, Alberta, Canada
- Department of Medical Physics, Cross Cancer Institute, Edmonton, Alberta, Canada
| | - Michael W Reynolds
- Department of Medical Physics, Cross Cancer Institute, Edmonton, Alberta, Canada
- Department of Radiation Oncology, BC Cancer - Victoria, Victoria, British Columbia, Canada
| | - David Sinn
- Department of Medical Physics, Cross Cancer Institute, Edmonton, Alberta, Canada
- Department of Radiaiton Oncology, The Queen's Medical Centre, Honolulu, Hawaii, USA
| | - Brad R Murray
- MagnetTx Oncology Solutions, Edmonton, Alberta, Canada
| | - B Gino Fallone
- Department of Oncology, Medical Physics Division, University of Alberta, Edmonton, Alberta, Canada
- Department of Medical Physics, Cross Cancer Institute, Edmonton, Alberta, Canada
- MagnetTx Oncology Solutions, Edmonton, Alberta, Canada
| | - Patricia Ak Oliver
- Department of Oncology, Medical Physics Division, University of Alberta, Edmonton, Alberta, Canada
- Department of Medical Physics, Cross Cancer Institute, Edmonton, Alberta, Canada
- Department of Medical Physics, Nova Scotia Health, Halifax, Nova Scotia, Canada
| |
Collapse
|
2
|
Kodama T, Yasui K, Nishioka S, Miyaura K, Takakura T, Katayose T, Nakamura M. Survey on utilization of flattening filter-free photon beams in Japan. JOURNAL OF RADIATION RESEARCH 2021; 62:726-734. [PMID: 34036361 PMCID: PMC8273795 DOI: 10.1093/jrr/rrab042] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/20/2021] [Revised: 03/08/2021] [Indexed: 06/12/2023]
Abstract
To understand the current state of flattening filter-free (FFF) beam implementation in C-arm linear accelerators (LINAC) in Japan, the quality assurance (QA)/quality control (QC) 2018-2019 Committee of the Japan Society of Medical Physics (JSMP) conducted a 37-question survey, designed to investigate facility information and specifications regarding FFF beam adoption and usage. The survey comprised six sections: facility information, devices, clinical usage, standard calibration protocols, modeling for treatment planning (TPS) systems and commissioning and QA/QC. A web-based questionnaire was developed. Responses were collected between 18 June and 18 September 2019. Of the 846 institutions implementing external radiotherapy, 323 replied. Of these institutions, 92 had adopted FFF beams and 66 had treated patients using them. FFF beams were used in stereotactic radiation therapy (SRT) for almost all disease sites, especially for the lungs using 6 MV and liver using 10 MV in 51 and 32 institutions, respectively. The number of institutions using FFF beams for treatment increased yearly, from eight before 2015 to 60 in 2018. Farmer-type ionization chambers were used as the standard calibration protocol in 66 (72%) institutions. In 73 (80%) institutions, the beam-quality conversion factor for FFF beams was calculated from TPR20,10, via the same protocol used for beams with flattening filter (WFF). Commissioning, periodic QA and patient-specific QA for FFF beams also followed the procedures used for WFF beams. FFF beams were primarily used in high-volume centers for SRT. In most institutions, measurement and QA was conducted via the procedures used for WFF beams.
Collapse
Affiliation(s)
- Takumi Kodama
- Department of Radiation Oncology, Saitama Cancer Center, 780 Ooazakomuro, Inamachi, Kitaadachi-gun, Saitama 362-0806, Japan
| | - Keisuke Yasui
- Faculty of Radiological Technology, School of Health Science, Fujita Health University, 1-98 Dengakugakubo, Kutsukake-cho, Toyoake, Aichi 470–1192, Japan
| | - Shie Nishioka
- Department of Medical Physics, National Cancer Center Hospital, 5-1-1 Tsukiji, Chuo-ku, Tokyo 104–0045, Japan
| | - Kazunori Miyaura
- Graduate School of Health Sciences, Showa University, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142–8666, Japan
| | - Toru Takakura
- Department of Radiation Therapy, Uji-Tokushukai Medical Center, 145 Ishibashi, Makichima-cho, Uji-shi, Kyoto 611–0041, Japan
| | - Tetsurou Katayose
- Department of Radiation Oncology, Chiba Cancer Center, 666-2 Nitona-cho, Chuo-ku, Chiba 260–8717, Japan
| | - Mitsuhiro Nakamura
- Department of Information Technology and Medical engineering, Human Health Science, Graduate School of Medicine, Kyoto University, 53 Shogoin Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan
| |
Collapse
|
3
|
Mizuno H, Yamashita W, Okuyama H, Takase N, Tohyama N, Shimizu H, Fujita Y, Kito S, Nakaji T, Fukuda S. Dose response of a radiophotoluminescent glass dosimeter for TomoTherapy, CyberKnife, and flattening-filter-free linear accelerator output measurements in dosimetry audit. Phys Med 2021; 88:91-97. [PMID: 34214838 DOI: 10.1016/j.ejmp.2021.06.010] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/12/2021] [Revised: 05/11/2021] [Accepted: 06/04/2021] [Indexed: 11/19/2022] Open
Abstract
PURPOSE We experimentally determined the radiophotoluminescent glass dosimeter (RPLD) dose responses for TomoTherapy, CyberKnife, and flattening-filter-free (FFF) linear accelerator (linac) outputs for dosimetry audits in Japan. METHODS A custom-made solid phantom with a narrow central-axis spacing of three RPLD elements was used for output measurement to minimise the dose-gradient effect of the non-flattening filter beams. For RPLD dose estimation, we used the ISO 22127 formalism. Additional unit-specific correction factors were introduced and determined via the measured data. For TomoTherapy (7 units) and CyberKnife (4 units), the doses were measured under machine-specific reference fields. For FFF linac (5 units), in addition to the reference condition, we obtained the field-size effects for the range from 5×5 cm to 25×25 cm. RESULTS The correction factors were estimated as 1.008 and 0.999 for TomoTherapy and CyberKnife, respectively. For FFF linac, they ranged from 1.011 to 0.988 for 6 MV and from 1.011 to 0.997 for 10 MV as a function of the side length of the square field from 5 to 25 cm. The estimated uncertainties of the absorbed dose to water measured by RPLD for the units were 1.32%, 1.35%, and 1.30% for TomoTherapy, CyberKnife, and FFF linac, respectively. A summary of the dosimetry audits of these treatment units using the obtained correction factors is also presented. The average percentage differences between the measured and hospital-stated doses were <1% under all conditions. CONCLUSION RPLD can be successfully used as a dosimetry audit tool for modern treatment units.
Collapse
Affiliation(s)
- Hideyuki Mizuno
- QST Hospital, National Institutes for Quantum and Radiological Science and Technology, Japan.
| | | | | | | | - Naoki Tohyama
- Tokyo Bay Advanced Imaging & Radiation Oncology Makuhari Clinic, Japan
| | | | | | - Satoshi Kito
- Tokyo Metropolitan Cancer and Infectious Diseases Center Komagome Hospital, Japan; Graduate School of Medicine, Kyoto University, Japan
| | - Taku Nakaji
- QST Hospital, National Institutes for Quantum and Radiological Science and Technology, Japan
| | - Shigekazu Fukuda
- QST Hospital, National Institutes for Quantum and Radiological Science and Technology, Japan
| |
Collapse
|
4
|
Buchegger N, Grogan G, Hug B, Oliver C, Ebert M. CyberKnife reference dosimetry: An assessment of the impact of evolving recommendations on correction factors and measured dose. Med Phys 2020; 47:3573-3585. [DOI: 10.1002/mp.14190] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2019] [Revised: 03/29/2020] [Accepted: 03/30/2020] [Indexed: 11/06/2022] Open
Affiliation(s)
- Nicole Buchegger
- Department of Radiation Oncology Sir Charles Gairdner Hospital Nedlands WA 6009 Australia
| | - Garry Grogan
- Department of Radiation Oncology Sir Charles Gairdner Hospital Nedlands WA 6009 Australia
| | - Ben Hug
- 5D Clinics Claremont WA 6010 Australia
| | - Chris Oliver
- Australian Radiation Protection and Nuclear Safety Agency Yallambie Vic. 3085 Australia
| | - Martin Ebert
- Department of Radiation Oncology Sir Charles Gairdner Hospital Nedlands WA 6009 Australia
- 5D Clinics Claremont WA 6010 Australia
- Department of Physics University of Western Australia Crawley WA 6009 Australia
| |
Collapse
|
5
|
Swanpalmer J. Reference dose determination in 60Co and high-energy radiotherapy photon beams by using Farmer-type cylindrical ionization chambers - an experimental investigation. Biomed Phys Eng Express 2020; 6:045003. [PMID: 33444264 DOI: 10.1088/2057-1976/ab8b25] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Ionization chamber dosimetry is predominantly used for determination of the absorbed dose to water in 60Co and high-energy radiotherapy photon beams. The most widespread ionization chambers employed for absolute or reference dose determinations in reference conditions are the Farmer-type cylindrical ionization chambers. The Farmer-type ionization chambers have a variety of constructions and materials and their responses vary in the radiation beam. Clinical accelerators, in addition to conventional photon beams with flattening-filter, can also deliver flattening-filter-free (FFF) photon beams. The responses of five different Farmer-type cylindrical ionization chambers were experimentally examined with reference to absorbed dose determination in reference conditions when using the International Atomic Energy Agency (IAEA) - American Association of Physicists in Medicine (AAPM) Technical Reports Series no. 483 (TRS-483) and the IAEA TRS-398 dosimetry protocol in the present investigation. The irradiations were performed using 60Co and megavoltage photon beams with 6 MV, 15 MV, 6 MV FFF and 10 MV FFF nominal photon energies. The chamber calibrations were performed at different Secondary Standard Dosimetry Laboratories and are traceable to primary standards at different Primary Standard Dosimetry Laboratories. The chambers were also cross-calibrated at our laboratory using 60Co γ-beam. The variation found in the data regarding the reference dose determination using the various Farmer-type chambers in the photon beams employed was about 1% at maximum. Thus, the selection of the ionization chamber in reference dose determinations may affect the outcomes. The differences in the absorbed dose values were similar in the conventional as well as in the FFF photon beams. For the FFF photon beams the absorbed dose computations were performed using the IAEA-AAPM TRS-483 dosimetry protocol. Two of the ionization chambers used had identical construction but different central electrodes, i.e. graphite versus aluminium. The results obtained using these two chambers show that, in the photon beams examined, the employed correction for the central electrode (p cel ) regarding these two chambers is associated with an inaccuracy which is larger than the calculated uncertainty for this correction. The outcomes found in the present experimental investigation using the various ionization chambers also indicate possible inaccuracy in the employed beam quality correction factors (k Q ) and imply the need for a revision of these factors.
Collapse
Affiliation(s)
- John Swanpalmer
- Sahlgrenska University Hospital, Department of Medical Physics and Biomedical Engineering, Gothenburg, Sweden. Department of Radiation Physics, Sahlgrenska Academy, University of Gothenburg, Sweden
| |
Collapse
|
6
|
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
| |
Collapse
|
7
|
de Prez L, de Pooter J, Jansen B, Perik T, Wittkämper F. Comparison of k Q factors measured with a water calorimeter in flattening filter free (FFF) and conventional flattening filter (cFF) photon beams. Phys Med Biol 2018; 63:045023. [PMID: 29461974 DOI: 10.1088/1361-6560/aaaa93] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Recently flattening filter free (FFF) beams became available for application in modern radiotherapy. There are several advantages of FFF beams over conventional flattening filtered (cFF) beams, however differences in beam spectra at the point of interest in a phantom potentially affect the ion chamber response. Beams are also non-uniform over the length of a typical reference ion chamber and recombination is usually larger. Despite several studies describing FFF beam characteristics, only a limited number of studies investigated their effect on k Q factors. Some of those studies predicted significant discrepancies in k Q factors (0.4% up to 1.0%) if TPR20,10 based codes of practice (CoPs) were to be used. This study addresses the question to which extent k Q factors, based on a TPR20,10 CoP, can be applied in clinical reference dosimetry. It is the first study that compares k Q factors measured directly with an absorbed dose to water primary standard in FFF-cFF pairs of clinical photon beams. This was done with a transportable water calorimeter described elsewhere. The measurements corrected for recombination and beam radial non-uniformity were performed in FFF-cFF beam pairs at 6 MV and 10 MV of an Elekta Versa HD for a selection of three different Farmer-type ion chambers (eight serial numbers). The ratio of measured k Q factors of the FFF-cFF beam pairs were compared with the TPR20,10 CoPs of the NCS and IAEA and the %dd(10) x CoP of the AAPM. For the TPR20,10 based CoPs differences less than 0.23% were found in k Q factors between the corresponding FFF-cFF beams with standard uncertainties smaller than 0.35%, while for the %dd(10) x these differences were smaller than 0.46% and within the expanded uncertainty of the measurements. Based on the measurements made with the equipment described in this study the authors conclude that the k Q factors provided by the NCS-18 and IAEA TRS-398 codes of practice can be applied for flattening filter free beams without additional correction. However, existing codes of practice cannot be applied ignoring the significant volume averaging effect of the FFF beams over the ion chamber cavity. For this a corresponding volume averaging correction must be applied.
Collapse
Affiliation(s)
- Leon de Prez
- VSL-Dutch Metrology Institute, Delft, Netherlands
| | | | | | | | | |
Collapse
|
8
|
Lechner W, Kuess P, Georg D, Palmans H. Equivalent (uniform) square field sizes of flattening filter free photon beams. ACTA ACUST UNITED AC 2017; 62:7694-7713. [DOI: 10.1088/1361-6560/aa83f5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
|
9
|
Czarnecki D, Poppe B, Zink K. Monte Carlo-based investigations on the impact of removing the flattening filter on beam quality specifiers for photon beam dosimetry. Med Phys 2017; 44:2569-2580. [DOI: 10.1002/mp.12252] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2016] [Revised: 03/13/2017] [Accepted: 03/21/2017] [Indexed: 01/07/2023] Open
Affiliation(s)
- Damian Czarnecki
- Institute of Medical Physics and Radiation Protection; University of Applied Sciences Giessen; Wiesenstrasse 14 Giessen D-35390 Germany
- University Clinic for Medical Radiation Physics; Medical Campus Pius Hospital; Carl von Ossietzky University; Oldenburg Germany
| | - Björn Poppe
- University Clinic for Medical Radiation Physics; Medical Campus Pius Hospital; Carl von Ossietzky University; Oldenburg Germany
| | - Klemens Zink
- Institute of Medical Physics and Radiation Protection; University of Applied Sciences Giessen; Giessen D-35390 Germany
- Department of Radiotherapy and Radiation Oncology; University Medical Center Giessen and Marburg; Marburg D-35043 Germany
- Frankfurt Institute for Advanced Studies (FIAS); Ruth-Moufang-Straße 1; 60438 Frankfurt am Main Germany
| |
Collapse
|
10
|
O'Brien DJ, Roberts DA, Ibbott GS, Sawakuchi GO. Reference dosimetry in magnetic fields: formalism and ionization chamber correction factors. Med Phys 2017; 43:4915. [PMID: 27487908 DOI: 10.1118/1.4959785] [Citation(s) in RCA: 123] [Impact Index Per Article: 17.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE Magnetic resonance imaging-guided radiotherapy (MRIgRT) provides superior soft-tissue contrast and real-time imaging compared with standard image-guided RT, which uses x-ray based imaging. Several groups are developing integrated MRIgRT machines. Reference dosimetry with these new machines requires accounting for the effects of the magnetic field on the response of the ionization chambers used for dose calibration. Here, the authors propose a formalism for reference dosimetry with integrated MRIgRT devices. The authors also examined the suitability of the TPR10 (20) and %dd(10)x beam quality specifiers in the presence of magnetic fields and calculated detector correction factors to account for the effects of the magnetic field for a range of detectors. METHODS The authors used full-head and point-source Monte Carlo models of an MR-linac along with detailed detector models of an Exradin A19, an NE2571, and several PTW Farmer chambers to calculate magnetic field correction factors for six commercial ionization chambers in three chamber configurations. Calculations of ionization chamber response (performed with geant4) were validated with specialized Fano cavity tests. %dd(10)x values, TPR10 (20) values, and Spencer-Attix water-to-air restricted stopping power ratios were also calculated. The results were further validated against measurements made with a preclinical functioning MR-linac. RESULTS The TPR10 (20) was found to be insensitive to the presence of the magnetic field, whereas the relative change in %dd(10)x was 2.4% when a transverse 1.5 T field was applied. The parameters chosen for the ionization chamber calculations passed the Fano cavity test to within ∼0.1%. Magnetic field correction factors varied in magnitude with detector orientation with the smallest corrections found when the chamber was parallel to the magnetic field. CONCLUSIONS Reference dosimetry can be performed with integrated MRIgRT devices by using magnetic field correction factors, but care must be taken with the choice of beam quality specifier and chamber orientation. The uncertainties achievable under this formalism should be similar to those of conventional formalisms, although this must be further quantified.
Collapse
Affiliation(s)
- D J O'Brien
- Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030
| | - D A Roberts
- Elekta Limited, Crawley, West Sussex RH10 9RR, United Kingdom
| | - G S Ibbott
- Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030
| | - G O Sawakuchi
- Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030 and Graduate School of Biomedical Sciences, The University of Texas, Houston, Texas 77030
| |
Collapse
|
11
|
Vargas Castrillón S, Cutanda Henríquez F. Choice of a Suitable Dosimeter for Photon Percentage Depth Dose Measurements in Flattening Filter-Free Beams. J Med Phys 2017; 42:140-143. [PMID: 28974859 PMCID: PMC5618460 DOI: 10.4103/jmp.jmp_11_17] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
The International Atomic Energy Agency Technical Reports Series-398 code of practice for dosimetry recommends measuring photon percentage depth dose (PDD) curves with parallel-plate chambers. This code of practice was published before flattening filter-free (FFF) beams were widely used in clinical linear accelerators. The choice of detector for PDD measurements needs to be reassessed for FFF beams given the physical differences between FFF beams and flattened ones. The present study compares PDD curves for FFF beams of nominal energies 6 MV, 6 FFF, 10 MV, and 10 FFF from a Varian TrueBeam linear accelerator (Varian Medical Systems, Palo Alto, USA) acquired with Scanditronix photon diodes, two scanning type chambers (both PTW 31010 Semiflex), two small volume chambers (Wellhofer CC04 and PTW 31016 PinPoint 3D), PTW 34001 Roos, Scanditronix Roos, and NACP 02 parallel-plate chambers. Results show that parallel-plate ion chambers can be used for photon PDD measurements, although for better accuracy, recombination effects should be taken into account.
Collapse
|
12
|
Sudhyadhom A, Kirby N, Faddegon B, Chuang CF. Technical Note: Preferred dosimeter size and associated correction factors in commissioning high dose per pulse, flattening filter free x-ray beams. Med Phys 2016; 43:1507-13. [PMID: 26936734 DOI: 10.1118/1.4941691] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE High dose rate flattening filter free (FFF) beams pose new challenges and considerations for accurate reference and relative dosimetry. The authors report errors associated with commonly used ion chambers and introduce simple methods to mitigate them. METHODS Dosimetric errors due to (1) ion recombination effects of high dose per pulse (DPP) FFF beams and (2) volume-averaging effects of the radial profile were examined on a TrueBeam STx. Four commonly used cylindrical ion chambers spanning a range of lengths (0.29-2.3 cm) and volumes (0.016-0.6 cm(3)) were used to determine the magnitude of these effects for 6 and 10 MV unflattened x-ray beams (6XFFF and 10XFFF, respectively). Two methods were used to determine the magnitude of ion collection efficiency: (1) direct measurement of the percent depth dose (PDD) for the clinical, high DPP beam in comparison to that obtained after reducing the DPP and (2) measurement of Pion as a function of depth. Two methods were used to quantify the magnitude of volume-averaging: (1) direct measurement of volume-averaging via cross-calibration and (2) calculation of volume-averaging from radial profiles of the beam. Finally, a simple analytical expression for the radial profile volume-averaging correction factor, Prp = [OAR(0.29L)](-1), or the inverse of the off-axis ratio of dose at 0.29L, where L is the length of the chamber's sensitive volume, is introduced to mitigate the volume-averaging effect in Farmer-type chambers. RESULTS Errors in measured PDD for the clinical beams were 1.3% ± 0.07% and 1.6% ± 0.07% at 35 cm depth for the 6XFFF and 10XFFF beam, respectively, using an IBA CC13 ion chamber, due to charge recombination with a high DPP. Volume-averaging effects were 0.4% and 0.7% for the 6XFFF and 10XFFF beam, respectively, when measured with a Farmer-type chamber. For the application of TG-51, these errors combine when using a CC13 to measure the PDD and a Farmer for absolute output dosimetry for a total error of up to 2% at dmax for the 10XFFF beam. CONCLUSIONS Relative and absolute dosimetry in high DPP, unflattened x-ray beams of 10 MV or higher requires corrections for charge recombination and/or volume-averaging when dosimeters with certain geometries are used. Chambers used for PDD measurement are available that do not require a correction for charge recombination. A simple analytical expression of the correction factor Prp was introduced in this work to account for volume-averaging effects in Farmer chambers. Choice of an appropriate dosimeter coupled with application of the established correction factors Pion and Prp reduces the uncertainty in the PDD measurement and the reference dose measurement.
Collapse
Affiliation(s)
- A Sudhyadhom
- Department of Radiation Oncology, University of California, San Francisco, San Francisco, California 94115
| | - N Kirby
- Department of Radiation Oncology, University of California, San Francisco, San Francisco, California 94115 and Department of Radiation Oncology and Radiology, UTHSCSA, San Antonio, San Antonio, Texas 78229
| | - B Faddegon
- Department of Radiation Oncology, University of California, San Francisco, San Francisco, California 94115
| | - C F Chuang
- Department of Radiation Oncology, University of California, San Francisco, San Francisco, California 94115
| |
Collapse
|
13
|
Pantelis E, Moutsatsos A, Zourari K, Kilby W, Antypas C, Papagiannis P, Karaiskos P, Georgiou E, Sakelliou L. On the implementation of a recently proposed dosimetric formalism to a robotic radiosurgery system. Med Phys 2016; 37:2369-79. [DOI: 10.1118/1.3404289] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
|
14
|
Kuess P, Georg D, Palmans H, Lechner W. Technical Note: On the impact of the incident electron beam energy on the primary dose component of flattening filter free photon beams. Med Phys 2016; 43:4507. [PMID: 27487867 DOI: 10.1118/1.4954849] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE For commercially available linear accelerators (Linacs), the electron energies of flattening filter free (FFF) and flattened (FF) beams are either identical or the electron energy of the FFF beam is increased to match the percentage depth dose curve (PDD) of the FF beam (in reference geometry). This study focuses on the primary dose components of FFF beams for both kinds of settings, studied on the same Linac. METHODS The measurements were conducted on a VersaHD Linac (Elekta, Crawley, UK) for both FF and FFF beams with nominal energies of 6 and 10 MV. In the clinical setting of the VersaHD, the energy of FFFM (Matched) beams is set to match the PDDs of the FF beams. In contrast the incident electron beam of the FFFU beam was set to the same energy as for the FF beam. Half value layers (HVLs) and a dual parameter beam quality specifier (DPBQS) were determined. RESULTS For the 6 MV FFFM beam, HVL and DPBQS values were very similar compared to those of the 6 MV FF beam, while for the 10 MV FFFM and FF beams, only %dd(10)x and HVL values were comparable (differences below 1.5%). This shows that matching the PDD at one depth does not guarantee other beam quality dependent parameters to be matched. For FFFU beams, all investigated beam quality specifiers were significantly different compared to those for FF beams of the same nominal accelerator potential. The DPBQS of the 6 MV FF and FFFM beams was equal within the measurement uncertainty and was comparable to published data of a machine with similar TPR20,10 and %dd(10)x. In contrast to that, the DPBQS's two parameters of the 10 MV FFFM beam were substantially higher compared to those for the 10 MV FF beam. CONCLUSIONS PDD-matched FF and FFF beams of both nominal accelerator potentials were observed to have similar HVL values, indicating similarity of their primary dose components. Using the DPBQS revealed that the mean attenuation coefficient was found to be the same within the uncertainty of 0.8% for 6 MV FF and 6 MV FFFM beams, while for 10 MV beams, they differed by 6.4%. This shows that the DPBQS can provide a differentiation of photon beam characteristics that would remain hidden by the use of a single beam quality specifier, such as %dd(10)x or HVL.
Collapse
Affiliation(s)
- Peter Kuess
- Department of Radiation Oncology, Division Medical Physics, Medical University Vienna, Vienna 1090, Austria and Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Medical University of Vienna, Vienna 1090, Austria
| | - Dietmar Georg
- Department of Radiation Oncology, Division Medical Physics, Medical University Vienna, Vienna 1090, Austria and Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Medical University of Vienna, Vienna 1090, Austria
| | - Hugo Palmans
- EBG MedAustron GmbH, Wiener Neustadt 2700, Austria and National Physical Laboratory, Teddington TW 11 0LW, United Kingdom
| | - Wolfgang Lechner
- Department of Radiation Oncology, Division Medical Physics, Medical University Vienna, Vienna 1090, Austria and Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Medical University of Vienna, Vienna 1090, Austria
| |
Collapse
|
15
|
Lye JE, Butler DJ, Oliver CP, Alves A, Lehmann J, Gibbons FP, Williams IM. Comparison between the TRS-398 code of practice and the TG-51 dosimetry protocol for flattening filter free beams. Phys Med Biol 2016; 61:N362-72. [DOI: 10.1088/0031-9155/61/14/n362] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
|
16
|
Valdenaire S, Mailleux H, Fau P. Modeling of flattening filter free photon beams with analytical and Monte Carlo TPS. Biomed Phys Eng Express 2016. [DOI: 10.1088/2057-1976/2/3/035010] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
|
17
|
Saenz DL, Narayanasamy G, Cruz W, Papanikolaou N, Stathakis S. Pinnacle3 modeling and end-to-end dosimetric testing of a Versa HD linear accelerator with the Agility head and flattening filter-free modes. J Appl Clin Med Phys 2016; 17:192-206. [PMID: 26894352 PMCID: PMC5690210 DOI: 10.1120/jacmp.v17i1.5808] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2015] [Revised: 08/27/2015] [Accepted: 08/26/2015] [Indexed: 11/23/2022] Open
Abstract
The Elekta Versa HD incorporates a variety of upgrades to the line of Elekta linear accelerators, primarily including the Agility head and flattening filter‐free (FFF) photon beam delivery. The completely distinct dosimetric output of the head from its predecessors, combined with the FFF beams, requires a new investigation of modeling in treatment planning systems. A model was created in Pinnacle3 v9.8 with the commissioned beam data. A phantom consisting of several plastic water and Styrofoam slabs was scanned and imported into Pinnacle3, where beams of different field sizes, source‐to‐surface distances (SSDs), wedges, and gantry angles were devised. Beams included all of the available photon energies (6, 10, 18, 6 FFF, and 10 FFF MV), as well as the four electron energies commissioned for clinical use (6, 9, 12, and 15 MeV). The plans were verified at calculation points by measurement with a calibrated ionization chamber. Homogeneous and heterogeneous point‐dose measurements agreed within 2% relative to maximum dose for all photon and electron beams. AP photon open field measurements along the central axis at 100 cm SSD passed within 1%. In addition, IMRT testing was also performed with three standard plans (step and shoot IMRT, as well as a small‐ and large‐field VMAT plan). The IMRT plans were delivered on the Delta4 IMRT QA phantom, for which a gamma passing rate was >99.5% for all plans with a 3% dose deviation, 3 mm distance‐to‐agreement, and 10% dose threshold. The IMRT QA results for the first 23 patients yielded gamma passing rates of 97.4%±2.3%. Such testing ensures confidence in the ability of Pinnacle3 to model photon and electron beams with the Agility head. PACS numbers: 87.55.D, 87.56.bd
Collapse
Affiliation(s)
- Daniel L Saenz
- University of Texas Health Science Center - San Antonio.
| | | | | | | | | |
Collapse
|
18
|
Eaton DJ, Thomas RAS, Duane S. Multi-centre audit of absolute dose calibration for flattening filter-free photon beams. Biomed Phys Eng Express 2015. [DOI: 10.1088/2057-1976/1/4/047002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
|
19
|
Ganesan R, McEwen MR, Orton CG. Point/Counterpoint. Calibration of radiotherapy ionization chambers using Co-60 is outdated and should be replaced by direct calibration in linear accelerator beams. Med Phys 2015; 42:5003-6. [PMID: 26328950 DOI: 10.1118/1.4922710] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Affiliation(s)
- Ramanathan Ganesan
- Radiotherapy Section, Medical Radiation Services Branch, Australian Radiation Protection and Nuclear Safety Agency, Yallambie 3085, Victoria, Australia (Tel: 61 3 9433 2273; E-mail: )
| | - Malcolm R McEwen
- Ionizing Radiation Standards, National Research Council, Ottawa, Ontario K1A OR6, Canada (Tel: 613-993-2197 Ext: 226; E-mail: )
| | | |
Collapse
|
20
|
Simpson E, Gajewski R, Flower E, Stensmyr R. Experimental validation of the dual parameter beam quality specifier for reference dosimetry in flattening-filter-free (FFF) photon beams. Phys Med Biol 2015; 60:N271-81. [DOI: 10.1088/0031-9155/60/14/n271] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
|
21
|
Xiao Y, Kry SF, Popple R, Yorke E, Papanikolaou N, Stathakis S, Xia P, Huq S, Bayouth J, Galvin J, Yin FF. Flattening filter-free accelerators: a report from the AAPM Therapy Emerging Technology Assessment Work Group. J Appl Clin Med Phys 2015; 16:5219. [PMID: 26103482 PMCID: PMC5690108 DOI: 10.1120/jacmp.v16i3.5219] [Citation(s) in RCA: 108] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2014] [Revised: 02/06/2015] [Accepted: 01/23/2015] [Indexed: 11/23/2022] Open
Abstract
This report describes the current state of flattening filter‐free (FFF) radiotherapy beams implemented on conventional linear accelerators, and is aimed primarily at practicing medical physicists. The Therapy Emerging Technology Assessment Work Group of the American Association of Physicists in Medicine (AAPM) formed a writing group to assess FFF technology. The published literature on FFF technology was reviewed, along with technical specifications provided by vendors. Based on this information, supplemented by the clinical experience of the group members, consensus guidelines and recommendations for implementation of FFF technology were developed. Areas in need of further investigation were identified. Removing the flattening filter increases beam intensity, especially near the central axis. Increased intensity reduces treatment time, especially for high‐dose stereotactic radiotherapy/radiosurgery (SRT/SRS). Furthermore, removing the flattening filter reduces out‐of‐field dose and improves beam modeling accuracy. FFF beams are advantageous for small field (e.g., SRS) treatments and are appropriate for intensity‐modulated radiotherapy (IMRT). For conventional 3D radiotherapy of large targets, FFF beams may be disadvantageous compared to flattened beams because of the heterogeneity of FFF beam across the target (unless modulation is employed). For any application, the nonflat beam characteristics and substantially higher dose rates require consideration during the commissioning and quality assurance processes relative to flattened beams, and the appropriate clinical use of the technology needs to be identified. Consideration also needs to be given to these unique characteristics when undertaking facility planning. Several areas still warrant further research and development. Recommendations pertinent to FFF technology, including acceptance testing, commissioning, quality assurance, radiation safety, and facility planning, are presented. Examples of clinical applications are provided. Several of the areas in which future research and development are needed are also indicated. PACS number: 87.53.‐j, 87.53.Bn, 87.53.Ly, 87.55.‐x, 87.55.N‐, 87.56.bc
Collapse
Affiliation(s)
- Ying Xiao
- Thomas Jefferson University Hospital.
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
22
|
Muralidhar KR. Derivation of equations to define inflection point and its analysis in flattening filter free photon beams based on the principle of polynomial function. INTERNATIONAL JOURNAL OF CANCER THERAPY AND ONCOLOGY 2014. [DOI: 10.14319/ijcto.0301.5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
|
23
|
Butler DJ, Ramanathan G, Oliver C, Cole A, Lye J, Harty PD, Wright T, Webb DV, Followill DS. Direct megavoltage photon calibration service in Australia. AUSTRALASIAN PHYSICAL & ENGINEERING SCIENCES IN MEDICINE 2014; 37:753-61. [PMID: 25146559 PMCID: PMC4297255 DOI: 10.1007/s13246-014-0293-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2014] [Accepted: 08/12/2014] [Indexed: 10/24/2022]
Abstract
The Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) maintains the Australian primary standard of absorbed dose. Until recently, the standard was used to calibrate ionisation chambers only in (60)Co gamma rays. These chambers are then used by radiotherapy clinics to determine linac output, using a correction factor (k Q) to take into account the different spectra of (60)Co and the linac. Over the period 2010-2013, ARPANSA adapted the primary standard to work in megavoltage linac beams, and has developed a calibration service at three photon beams (6, 10 and 18 MV) from an Elekta Synergy linac. We describe the details of the new calibration service, the method validation and the use of the new calibration factors with the International Atomic Energy Agency's TRS-398 dosimetry Code of Practice. The expected changes in absorbed dose measurements in the clinic when shifting from (60)Co to the direct calibration are determined. For a Farmer chamber (model 2571), the measured chamber calibration coefficient is expected to be reduced by 0.4, 1.0 and 1.1 % respectively for these three beams when compared to the factor derived from (60)Co. These results are in overall agreement with international absorbed dose standards and calculations by Muir and Rogers in 2010 of k Q factors using Monte Carlo techniques. The reasons for and against moving to the new service are discussed in the light of the requirements of clinical dosimetry.
Collapse
Affiliation(s)
- D J Butler
- Australian Radiation Protection and Nuclear Safety Agency, 619 Lower Plenty Road, Yallambie, VIC, 3085, Australia,
| | | | | | | | | | | | | | | | | |
Collapse
|
24
|
Dalaryd M, Knöös T, Ceberg C. Combining tissue-phantom ratios to provide a beam-quality specifier for flattening filter free photon beams. Med Phys 2014; 41:111716. [DOI: 10.1118/1.4898325] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
|
25
|
Fu G, Li M, Song Y, Dai J. A dosimetric evaluation of flattening filter-free volumetric modulated arc therapy in nasopharyngeal carcinoma. J Med Phys 2014; 39:150-5. [PMID: 25190993 PMCID: PMC4154182 DOI: 10.4103/0971-6203.139003] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2013] [Revised: 05/11/2014] [Accepted: 06/01/2014] [Indexed: 11/04/2022] Open
Abstract
PURPOSE To explore the dosimetric effects of flattening filter-free (FFF) beams in volumetric modulated arc therapy (VMAT) of nasopharyngeal carcinoma via a retrospective planning study. MATERIALS AND METHODS A linear accelerator (LINAC) was prepared to operate in FFF mode and the beam data were collected and used to build a model in TPS. For 10 nasopharyngeal carcinoma (NPC) cases, VMAT plans of FFF beams and normal flattened (FF) beams were designed. Differences of plan quality and delivery efficiency between FFF-VMAT plans and filter filtered VMAT (FF-VMAT) plans were analyzed using two-tailed paired t-tests. RESULTS Removal of the flattening filter increased the dose rate. Averaged beam on time (BOT) of FFF-VMAT plans was decreased by 24.2%. Differences of target dose coverage between plans with flattened and unflattened beams were statistically insignificant. For dose to normal organs, up to 4.9% decrease in V35 of parotid grand and 4.5% decrease in averaged normal tissue (NT) dose was observed. CONCLUSIONS The TPS used in our study was able to handle FFF beams. The FFF beam prone to improve the normal tissue sparing while achieving similar target dose distribution. Decreasing of BOT in NPC cases was valuable in terms of patient's comfort.
Collapse
Affiliation(s)
- Guishan Fu
- Department of Radiotherapy, Cancer Hospital and Institution, Chinese Academy of Medical Sciences, Panjiayuan NaiLi 17#, Chaoyang Dist, Beijing, China
| | - Minghui Li
- Department of Radiotherapy, Cancer Hospital and Institution, Chinese Academy of Medical Sciences, Panjiayuan NaiLi 17#, Chaoyang Dist, Beijing, China
| | - Yixin Song
- Department of Radiotherapy, Cancer Hospital and Institution, Chinese Academy of Medical Sciences, Panjiayuan NaiLi 17#, Chaoyang Dist, Beijing, China
| | - Jianrong Dai
- Department of Radiotherapy, Cancer Hospital and Institution, Chinese Academy of Medical Sciences, Panjiayuan NaiLi 17#, Chaoyang Dist, Beijing, China
| |
Collapse
|
26
|
McEwen M, DeWerd L, Ibbott G, Followill D, Rogers DWO, Seltzer S, Seuntjens J. Addendum to the AAPM's TG-51 protocol for clinical reference dosimetry of high-energy photon beams. Med Phys 2014; 41:041501. [PMID: 24694120 PMCID: PMC5148035 DOI: 10.1118/1.4866223] [Citation(s) in RCA: 200] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2013] [Revised: 02/03/2014] [Accepted: 02/06/2014] [Indexed: 11/07/2022] Open
Abstract
An addendum to the AAPM's TG-51 protocol for the determination of absorbed dose to water in megavoltage photon beams is presented. This addendum continues the procedure laid out in TG-51 but new kQ data for photon beams, based on Monte Carlo simulations, are presented and recommendations are given to improve the accuracy and consistency of the protocol's implementation. The components of the uncertainty budget in determining absorbed dose to water at the reference point are introduced and the magnitude of each component discussed. Finally, the consistency of experimental determination of ND,w coefficients is discussed. It is expected that the implementation of this addendum will be straightforward, assuming that the user is already familiar with TG-51. The changes introduced by this report are generally minor, although new recommendations could result in procedural changes for individual users. It is expected that the effort on the medical physicist's part to implement this addendum will not be significant and could be done as part of the annual linac calibration.
Collapse
Affiliation(s)
- Malcolm McEwen
- National Research Council, 1200 Montreal Road, Ottawa, Ontario, Canada
| | - Larry DeWerd
- University of Wisconsin, 1111 Highland Avenue, Madison, Wisconsin 53705
| | - Geoffrey Ibbott
- Department of Radiation Physics, M D Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, Texas 77030
| | - David Followill
- IROC Houston QA Center, Radiological Physics Center, 8060 El Rio Street, Houston, Texas 77054
| | - David W O Rogers
- Carleton Laboratory for Radiotherapy Physics, Physics Department, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario, Canada
| | - Stephen Seltzer
- National Institute of Standards and Technology, Gaithersburg, Maryland 20899
| | - Jan Seuntjens
- Medical Physics Unit, McGill University, 1650 Cedar Avenue, Montreal, Québec, Canada
| |
Collapse
|
27
|
Jank J, Kragl G, Georg D. Impact of a flattening filter free linear accelerator on structural shielding design. Z Med Phys 2014; 24:38-48. [DOI: 10.1016/j.zemedi.2013.05.002] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2012] [Revised: 05/16/2013] [Accepted: 05/17/2013] [Indexed: 10/26/2022]
|
28
|
Thomas SJ, Aspradakis MM, Byrne JP, Chalmers G, Duane S, Rogers J, Thomas RAS, Tudor GSJ, Twyman N. Reference dosimetry on TomoTherapy: an addendum to the 1990 UK MV dosimetry code of practice. Phys Med Biol 2014; 59:1339-52. [DOI: 10.1088/0031-9155/59/6/1339] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
|
29
|
Improvement of the penumbra for small radiosurgical fields using flattening filter free low megavoltage beams. Z Med Phys 2013; 23:291-9. [DOI: 10.1016/j.zemedi.2013.03.011] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2012] [Revised: 03/12/2013] [Accepted: 03/18/2013] [Indexed: 11/21/2022]
|
30
|
Beam quality and dose perturbation of 6 MV flattening-filter-free linac. Phys Med 2013; 30:47-56. [PMID: 23517668 DOI: 10.1016/j.ejmp.2013.02.004] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/16/2012] [Revised: 01/07/2013] [Accepted: 02/19/2013] [Indexed: 11/22/2022] Open
Abstract
The aim of this study is twofold: (a) determination of the spectral differences for flattening-filter-free (FFF) versus standard (STD) linac under various clinical conditions, (b) based on an extensive list of clinically important beam configurations, identification of clinical scenarios that lead to higher macroscopic dose perturbations due to the presence of high-Z material. The focus is on dose enhancement due to contrast agents including high-Z elements such as gold or gadolinium. EGSnrc was used to simulate clinical beams under various irradiation conditions: open/IMRT/spit-IMRT fields, in/out-off-field areas, different depths and field sizes. Spectra were calculated and analyzed for about 80 beams and for a total of 480 regions. Quantitative differential effects in beam quality were characterized using energy-dependent and cumulative dose perturbation metrics. Analysis of the spectral database showed that even though the general trends for both linacs (FFF/STD) were the same, there were crucial differences. In general, the relative changes between different conditions were smaller for FFF spectra. This was because of the higher component of low-energy photons of the FFF linac, which already lead to higher dose enhancement than for the STD linac (photon energies were more "uniformly" distributed for FFF spectra and henceforth their perturbation resulted in lesser relative changes). For out-of-field FFF spectra and split-IMRT fields the strongest enhancement were observed (∼25 and ∼5 respectively). Different spectral scenarios lead to different dose enhancements, however, they scale with the higher effective-Z of the materials and were directly related to the lower range of the spectra (<200 keV).
Collapse
|
31
|
Fogliata A, Garcia R, Knoos T, Nicolini G, Clivio A, Vanetti E, Khamphan C, Cozzi L. Definition of parameters for quality assurance of flattening filter free (FFF) photon beams in radiation therapy. Med Phys 2012; 39:6455-64. [PMID: 23039680 DOI: 10.1118/1.4754799] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE Flattening filter free (FFF) beams generated by medical linear accelerators have recently started to be used in radiotherapy clinical practice. Such beams present fundamental differences with respect to the standard filter flattened (FF) beams, making the generally used dosimetric parameters and definitions not always viable. The present study will propose possible definitions and suggestions for some dosimetric parameters for use in quality assurance of FFF beams generated by medical linacs in radiotherapy. METHODS The main characteristics of the photon beams have been analyzed using specific data generated by a Varian TrueBeam linac having both FFF and FF beams of 6 and 10 MV energy, respectively. RESULTS Definitions for dose profile parameters are suggested starting from the renormalization of the FFF with respect to the corresponding FF beam. From this point the flatness concept has been translated into one of "unflatness" and other definitions have been proposed, maintaining a strict parallelism between FFF and FF parameter concepts. CONCLUSIONS Ideas for quality controls used in establishing a quality assurance program when introducing FFF beams into the clinical environment are given here, keeping them similar to those used for standard FF beams. By following the suggestions in this report, the authors foresee that the introduction of FFF beams into a clinical radiotherapy environment will be as safe and well controlled as standard beam modalities using the existing guidelines.
Collapse
Affiliation(s)
- A Fogliata
- Oncology Institute of Southern Switzerland, Medical Physics Unit, Bellinzona CH-6500, Switzerland.
| | | | | | | | | | | | | | | |
Collapse
|
32
|
Huang Y, Siochi RA, Bayouth JE. Dosimetric properties of a beam quality-matched 6 MV unflattened photon beam. J Appl Clin Med Phys 2012; 13:3701. [PMID: 22766941 PMCID: PMC5716519 DOI: 10.1120/jacmp.v13i4.3701] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2011] [Revised: 03/23/2012] [Accepted: 04/10/2012] [Indexed: 11/23/2022] Open
Abstract
The purpose of this study was to report the characteristics of an equivalent quality unflattened (eqUF) photon beam in clinical implementation and to provide a generalized method to describe unflattened (UF) photon beam profiles. An unflattened photon beam with a beam quality equivalent to the corresponding flat 6 MV photon beam (WF) was obtained by removing the flattening filter from a Siemens ONCOR Avant‐Garde linear accelerator and adjusting the photon energy. A method independent from the WF beam profile was presented to describe UF beam profiles and other selected beam characteristics were examined. The short‐term beam stability was examined by dynamic beam profiles, recorded every 0.072 s in static and gated delivery, and the long‐term stability was evidenced by the five‐year clinical quality assurance records. The dose rate was raised fivefold using the eqUF beam. The depth of maximum dose (dmax) shifted 3 mm deeper, but the percent depth dose beyond dmax was very similar to that of the WF beam. The surface dose and out‐of‐field dose were lower, but the penumbra was slightly wider. The variation in head scatter and phantom scatter with changes in field size was smaller; the variation in the profile shape with change in depth was also smaller. The eqUF beam is stable 0.072 s after the beam is turned on, and the five‐year beam stability was comparable to that of the WF beam. A fivefold dose rate increase was observed in the eqUF beam with similar beam characteristics to other reported UF beam data except for a deeper dmax and a slightly wider penumbra. The initial and long‐term stability of the eqUF beam profile is on parity with the WF beam. The UF beam profile can be described in the generalized method independently without relying on the WF beam profile. PACS number: 87.55.de
Collapse
Affiliation(s)
- Yunfei Huang
- Department of Radiation Oncology, Division of Medical Physics, University of Iowa Hospitals and Clinics, Iowa City, Iowa 52242
| | | | | |
Collapse
|
33
|
Radiation therapy with unflattened photon beams: Dosimetric accuracy of advanced dose calculation algorithms. Radiother Oncol 2011; 100:417-23. [DOI: 10.1016/j.radonc.2011.09.001] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2011] [Revised: 08/30/2011] [Accepted: 09/02/2011] [Indexed: 11/15/2022]
|
34
|
Tsiamas P, Seco J, Han Z, Bhagwat M, Maddox J, Kappas C, Theodorou K, Makrigiorgos M, Marcus K, Zygmanski P. A modification of flattening filter free linac for IMRT. Med Phys 2011; 38:2342-52. [PMID: 21776768 DOI: 10.1118/1.3571419] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE This study investigates the benefits of a modified flattening filter free (FFF) linac over the standard (STD) linac equipped with the flattening filter. Energy and angular spread of the electron beam of the FFF linac were modified. Modification of FFF beam parameters is explored to maximize the monitor unit efficiency and to minimize the head scatter in IMRT delivery for large target volumes or targets lying away from the central axis. METHODS The EGSnrc code is used to model FFF and STD linacs and study basic beam properties for both linac types in various beam configurations. Increasing energy of FFF linac results in similar beam attenuation properties and maximized dose rate compared to STD linac. Matching beam attenuation properties allows a more direct exploration of beam flatness of FFF linac in regard to IMRT delivery, especially away from the central axis where the effective dose rate is considerably smaller than the one at the central axis. Flatness of open beam dose profile of FFF linac is improved by increasing the angular spread of the electron beam. The resulting dose rate within the treatment field and outside of the field (peripheral dose) are characterized and compared to the unmodified FFF and STD linacs, RESULTS In order to match beam penetration properties, the energy of FFF is adjusted from 6.5 to 8.0 MeV for small to medium field sizes and from 6.5 to 8.5 MeV for larger ones. Dose rate of FFF vs STD linac increased by a factor of 1.9 (6.5 MeV) and 3.4-4.1 (8.0-8.5 MeV). Adjusting the mean angular spread of the electron beam from 0 degrees to 5 degrees-10 degrees resulted in complete flattening of photon beam for field sizes between 10 x 10 cm2 and 15 x 15 cm2 and partial flattening for field sizes from 15 x 15 cm2 to 30 x 30 cm2. Values of angular spread > or =14 degrees are not recommended as they exceed the opening of the primary collimator, affecting the area at the edges of the field. FFF fields of sizes smaller than 6 x 6 cm2 are already flat and beam flattening is not necessary. Overall, the angular spread of 5 degrees-10 degrees is sufficient and can satisfactorily flatten open beam dose profiles even for larger field sizes. Increasing the electron beam angular spread amounts to a slight decrease of dose rate of FFF linac. However, for angular spread, 5 degrees-10 degrees dose rate factor of FFF vs STD is still about 1.6-2.6, depending on the field size (and the adjusted energy). Similarly, in case of peripheral dose, a moderate increase in dose can be observed for angular spread of 5 degrees-10 degrees and for field sizes 10 x 10 cm2 to 30 x 30 cm2. Lastly, beam flatness of not modified FFF linac can be conveniently described by an analytical function representing a ratio of STD vs FFF doses: 1 + b|r|(n). CONCLUSIONS A modified FFF beamline with increased energy and electron beam angular spread results in satisfactory flattened beam and high dose rate within the field. Peripheral dose remaining at similar (or smaller) level than that of STD linac for the same delivered dose within the treatment field.
Collapse
Affiliation(s)
- P Tsiamas
- Brigham and Women Hospital and Harvard Medical School, Boston, Massachusetts 02115, USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
35
|
Stevens SW, Rosser KE, Bedford JL. A 4 MV flattening filter-free beam: commissioning and application to conformal therapy and volumetric modulated arc therapy. Phys Med Biol 2011; 56:3809-24. [DOI: 10.1088/0031-9155/56/13/005] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
|
36
|
Georg D, Knöös T, McClean B. Current status and future perspective of flattening filter free photon beams. Med Phys 2011; 38:1280-93. [PMID: 21520840 DOI: 10.1118/1.3554643] [Citation(s) in RCA: 218] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE Flattening filters (FFs) have been considered as an integral part of the treatment head of a medical accelerator for more than 50 years. The reasons for the longstanding use are, however, historical ones. Advanced treatment techniques, such as stereotactic radiotherapy or intensity modulated radiotherapy have stimulated the interest in operating linear accelerators in a flattening filter free (FFF) mode. The current manuscript reviews treatment head physics of FFF beams, describes their characteristics and the resulting potential advantages in their medical use, and closes with an outlook. METHODS A number of dosimetric benefits have been determined for FFF beams, which range from increased dose rate and dose per pulse to favorable output ratio in-air variation with field size, reduced energy variation across the beam, and reduced leakage and out-of-field dose, respectively. Finally, the softer photon spectrum of unflattened beams has implications on imaging strategies and radiation protection. RESULTS The dosimetric characteristics of FFF beams have an effect on treatment delivery, patient comfort, dose calculation accuracy, beam matching, absorbed dose determination, treatment planning, machine specific quality assurance, imaging, and radiation protection. When considering conventional C-arm linacs in a FFF mode, more studies are needed to specify and quantify the clinical advantages, especially with respect to treatment plan quality and quality assurance. CONCLUSIONS New treatment units are already on the market that operate without a FF or can be operated in a dedicated clinical FFF mode. Due to the convincing arguments of removing the FF, it is expected that more vendors will offer dedicated treatment units for advanced photon beam therapy in the near future. Several aspects related to standardization, dosimetry, treatment planning, and optimization need to be addressed in more detail in order to facilitate the clinical implementation of unflattened beams.
Collapse
Affiliation(s)
- Dietmar Georg
- Department of Radiotherapy, Division of Medical Radiation Physics, Medical University of Vienna/AKH Vienna, A-1090 Vienna, Austria.
| | | | | |
Collapse
|
37
|
Muir BR, Rogers DWO. The central electrode correction factor for high-Z electrodes in small ionization chambers. Med Phys 2011; 38:1081-8. [DOI: 10.1118/1.3532818] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
|
38
|
Dalaryd M, Kragl G, Ceberg C, Georg D, McClean B, af Wetterstedt S, Wieslander E, Knöös T. A Monte Carlo study of a flattening filter-free linear accelerator verified with measurements. Phys Med Biol 2010; 55:7333-44. [PMID: 21081829 DOI: 10.1088/0031-9155/55/23/010] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
A Monte Carlo model of an Elekta Precise linear accelerator has been built and verified by measured data for a 6 and 10 MV photon beam running with and without a flattening filter in the beam line. In this study the flattening filter was replaced with a 6 mm thick copper plate, provided by the linac vendor, in order to stabilize the beam. Several studies have shown that removal of the filter improves some properties of the photon beam, which could be beneficial for radiotherapy treatments. The investigated characteristics of this new beam included output, spectra, mean energy, half value layer and the origin of scattered photons. The results showed an increased dose output per initial electron at the central axis of 1.76 and 2.66 for the 6 and 10 MV beams, respectively. The number of scattered photons from the accelerator head was reduced by (31.7 ± 0.03)% (1 SD) for the 6 MV beam and (47.6 ± 0.02)% for the 10 MV beam. The photon energy spectrum of the unflattened beam was softer compared to a conventional beam and did not vary significantly with the off-axis distance, even for the largest field size (0-20 cm off-axis).
Collapse
Affiliation(s)
- Mårten Dalaryd
- Radiation Physics, Skåne University Hospital and Lund University, Lund, Sweden.
| | | | | | | | | | | | | | | |
Collapse
|
39
|
Ceberg C, Johnsson S, Lind M, Knöös T. Prediction of stopping-power ratios in flattening-filter free beams. Med Phys 2010; 37:1164-8. [PMID: 20384253 DOI: 10.1118/1.3314074] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
PURPOSE In recent years, there has been an increasing interest in flattening-filter free (FFF) beams. However, since the removal of the flattening filter will affect both the mean and the variance of the energy spectrum, current beam-quality specifiers may not be adequate for reference dosimetry in such beams. The purpose of this work was to investigate an alternative, more general beam-quality specifier. METHODS The beam-quality specifier used in this work was a combination of the kerma-weighted mean and the coefficient of variation of the linear attenuation coefficient in water. These parameters can in theory be determined from narrow-beam transmission measurements using a miniphantom "in-air," which is a measurement condition well suited also to small and nonstandard fields. The relation between the Spencer-Attix stopping-power ratios and this novel beam-quality specifier was described by a simple polynomial. For reference, the authors used Monte Carlo calculated spectra and stopping-power data for nine different beams, with and without flattening filter. RESULTS The polynomial coefficients were obtained by least-squares optimization. For all beams included in this investigation, the average of the differences between the predicted and the Monte Carlo calculated stopping-power ratios was 0.02 +/- 0.17% (1 SD) (including TomoTherapy and CyberKnife example beams). CONCLUSIONS An alternative dual-parameter beam-quality specifier was investigated. The evaluation suggests that it can be used successfully to predict stopping-power ratios in FFF as well as conventional beams, regardless of filtration.
Collapse
Affiliation(s)
- Crister Ceberg
- Department of Medical Radiation Physics, Lund University, Box 117, SE-221 00 Lund, Sweden.
| | | | | | | |
Collapse
|
40
|
Kragl G, af Wetterstedt S, Knäusl B, Lind M, McCavana P, Knöös T, McClean B, Georg D. Dosimetric characteristics of 6 and 10MV unflattened photon beams. Radiother Oncol 2009; 93:141-6. [DOI: 10.1016/j.radonc.2009.06.008] [Citation(s) in RCA: 136] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2008] [Revised: 06/05/2009] [Accepted: 06/08/2009] [Indexed: 11/29/2022]
|