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Yadav N, Singh M, Mishra A, Mishra SP. Analysis of the gamma index using an indigenously developed anthropomorphic heterogeneous female pelvis (AHFP) phantom. J Cancer Res Ther 2024:01363817-990000000-00097. [PMID: 39207032 DOI: 10.4103/jcrt.jcrt_721_23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2023] [Accepted: 08/14/2023] [Indexed: 09/04/2024]
Abstract
BACKGROUND It is essential in modern radiotherapy treatment practices to evaluate the quality assurance (QA) of the treatment plan prior to the exclusion of patient from treatment. The typical suitable tools used for patient pretreatment QA are phantoms representing the human anatomy. An anthropomorphic heterogeneous female pelvic (AHFP) phantom has been developed to represent the real female pelvic structure. PURPOSE The objective of the current study is to assess the findings of relative dosimetry carried out utilizing an electronic portal imaging device (EPID) on the AHFP phantom fabricated. METHODS The planning target volume (PTV) was created on CT slices of an AHFP phantom to confirm the tool's ability to represent female pelvic anatomy and serve as a QA tool. In order to assess the dose received by healthy organs during radiotherapy, organs at risk such as the bladder and rectum were additionally drawn alongside the PTV. Rapid Arc and Intensity modulated radiation therapy (IMRT) were both used to create the treatment plan on treatment planning system, and the Anisotropic Analytical Algorithm Version 11.0.31 was used to calculate the dose. RESULTS The results obtained for the average gamma value in RapidArc plans are 0.26, 0.27, and 0.28 (g ≤1) and IMRT plans are 0.39, 0.40, and 0.46 (g ≤1) for target 1, target 2, and target 3, respectively. CONCLUSION According to the findings of the current study, the AHFP phantom was used to explore the potential of relative dosimetry using EPID as a QA tool, which was found to be suitable.
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Affiliation(s)
- Neha Yadav
- Department of Applied Physics, Amity School of Engineering and Technology, Amity University, Gwalior, Madhya Pradesh, India
| | - Manisha Singh
- Department of Applied Physics, Amity School of Engineering and Technology, Amity University, Gwalior, Madhya Pradesh, India
| | - Atul Mishra
- Department of Radiation Oncology, Uttar Pradesh University of Medical Sciences, Etawah, Uttar Pradesh, India
| | - Surendra Prasad Mishra
- Department of Radiation Oncology, Dr. Ram Manohar Lohia Institute of Medical Sciences, Lucknow, Uttar Pradesh, India
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Riis HL, Engstrøm KH, Slama L, Dass J, Ebert MA, Rowshanfarzad P. Assessing focal spot alignment in clinical linear accelerators: a comprehensive evaluation with triplet phantoms. Phys Eng Sci Med 2024:10.1007/s13246-024-01450-9. [PMID: 38954381 DOI: 10.1007/s13246-024-01450-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2024] [Accepted: 05/21/2024] [Indexed: 07/04/2024]
Abstract
A fundamental parameter to evaluate the beam delivery precision and stability on a clinical linear accelerator (linac) is the focal spot position (FSP) measured relative to the collimator axis of the radiation head. The aims of this work were to evaluate comprehensive data on FSP acquired on linacs in clinical use and to establish the ability of alternative phantoms to detect effects on patient plan delivery related to FSP. FSP measurements were conducted using a rigid phantom holding two ball-bearings at two different distances from the radiation source. Images of these ball-bearings were acquired using the electronic portal imaging device (EPID) integrated with each linac. Machine QA was assessed using a radiation head-mounted PTW STARCHECK phantom. Patient plan QA was investigated using the SNC ArcCHECK phantom positioned on the treatment couch, irradiated with VMAT plans across a complete 360° gantry rotation and three X-ray energies. This study covered eight Elekta linacs, including those with 6 MV, 18 MV, and 6 MV flattening-filter-free (FFF) beams. The largest range in the FSP was found for 6 MV FFF. The FSP of one linac, retrofitted with 6 MV FFF, displayed substantial differences in FSP compared to 6 MV FFF beams on other linacs, which all had FSP ranges less than 0.50 mm and 0.25 mm in the lateral and longitudinal directions, respectively. The PTW STARCHECK phantom proved effective in characterising the FSP, while the SNC ArcCHECK measurements could not discern FSP-related features. Minor variations in FSP may be attributed to adjustments in linac parameters, component replacements necessary for beam delivery, and the wear and tear of various linac components, including the magnetron and gun filament. Consideration should be given to the ability of any particular phantom to detect a subsequent impact on the accuracy of patient plan delivery.
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Affiliation(s)
- Hans L Riis
- Department of Oncology, Odense University Hospital, Odense, Denmark.
- Department of Clinical Research, University of Southern Denmark, Odense, Denmark.
- Radiofysisk Laboratorium, Odense University Hospital, Kløvervænget 19, DK-5000 Odense C, Odense, Denmark.
| | - Kenni H Engstrøm
- Department of Oncology, Odense University Hospital, Odense, Denmark
| | - Luke Slama
- Department of Radiation Oncology, Sir Charles Gairdner Hospital, Nedlands, WA, 6009, Australia
| | - Joshua Dass
- Department of Radiation Oncology, Sir Charles Gairdner Hospital, Nedlands, WA, 6009, Australia
- Centre for Advanced Technologies in Cancer Research (CATCR), Perth, WA, 6000, Australia
| | - Martin A Ebert
- Department of Radiation Oncology, Sir Charles Gairdner Hospital, Nedlands, WA, 6009, Australia
- Centre for Advanced Technologies in Cancer Research (CATCR), Perth, WA, 6000, Australia
- School of Physics, Mathematics, and Computing, The University of Western Australia, Crawley, WA, 6009, Australia
| | - Pejman Rowshanfarzad
- Centre for Advanced Technologies in Cancer Research (CATCR), Perth, WA, 6000, Australia
- School of Physics, Mathematics, and Computing, The University of Western Australia, Crawley, WA, 6009, Australia
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Lee S, Lovelock DM, Kowalski A, Chapman K, Foley R, Gil M, Pastrana G, Higginson DS, Yamada Y, Zhang L, Mechalakos J, Yorke E. Failure mode and effect analysis for linear accelerator-based paraspinal stereotactic body radiotherapy. J Appl Clin Med Phys 2021; 22:87-96. [PMID: 34708910 PMCID: PMC8664134 DOI: 10.1002/acm2.13455] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2021] [Revised: 09/21/2021] [Accepted: 10/06/2021] [Indexed: 12/31/2022] Open
Abstract
Introduction Paraspinal stereotactic body radiotherapy (SBRT) involves risks of severe complications. We evaluated the safety of the paraspinal SBRT program in a large academic hospital by applying failure modes and effects analysis. Methods The analysis was conducted by a multidisciplinary committee (two therapists, one dosimetrist, four physicists, and two radiation oncologists). The paraspinal SBRT workflow was segmented into four phases (simulation, treatment planning, delivery, and machine quality assurance (QA)). Each phase was further divided into a sequence of sub‐processes. Potential failure modes (PFM) were identified from each subprocess and scored in terms of the frequency of occurrence, severity and detectability, and a risk priority number (RPN). High‐risk PFMs were identified based on RPN and were studied for root causes using fault tree analysis. Results Our paraspinal SBRT process was characterized by eight simulations, 11 treatment planning, nine delivery, and two machine QA sub‐processes. There were 18, 29, 19, and eight PFMs identified from simulation, planning, treatment, and machine QA, respectively. The median RPN of the PFMs was 62.9 for simulation, 68.3 for planning, 52.9 for delivery, and 22.0 for machine QA. The three PFMs with the highest RPN were: previous radiotherapy outside the institution is not accurately evaluated (RPN: 293.3), incorrect registration between diagnostic magnetic resonance imaging and simulation computed tomography causing incorrect contours (273.0), and undetected patient movement before ExacTrac baseline (217.8). Remedies to the high RPN failures were implemented, including staff education, standardized magnetic resonance imaging acquisition parameters, and an image fusion process, and additional QA on beam steering. Conclusions A paraspinal SBRT workflow in a large clinic was evaluated using a multidisciplinary and systematic risk analysis, which led to feasible solutions to key root causes. Treatment planning was a major source of PFMs that systematically affect the safety and quality of treatments. Accurate evaluation of external treatment records remains a challenge.
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Affiliation(s)
- Sangkyu Lee
- Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, New York, USA
| | - Dale Michael Lovelock
- Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, New York, USA
| | - Alex Kowalski
- Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, New York, USA
| | - Kate Chapman
- Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, New York, USA
| | - Robert Foley
- Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, New York, USA
| | - Mary Gil
- Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, New York, USA
| | - Gerri Pastrana
- Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, New York, USA
| | - Daniel S Higginson
- Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, New York, USA
| | - Yoshiya Yamada
- Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, New York, USA
| | - Lei Zhang
- Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, New York, USA
| | - James Mechalakos
- Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, New York, USA
| | - Ellen Yorke
- Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, New York, USA
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Norvill C, Goodall S. Investigation of pixel scale calibration on the Elekta iView electronic portal imager. J Appl Clin Med Phys 2021; 22:148-155. [PMID: 34250752 PMCID: PMC8364275 DOI: 10.1002/acm2.13339] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Revised: 05/10/2021] [Accepted: 06/16/2021] [Indexed: 01/09/2023] Open
Abstract
This study investigated the variation in electronic portal imager pixel scale at the isocenter plane for Elekta Agility linear accelerators. An in‐house MATLAB script was written to process and calculate the pixel scale based on a metal calibration plate supplied by Elekta. Eight pixel plates were compared and found to have manufacturing tolerances within 0.1 mm of nominal dimensions. The impact of these variations on pixel scale factor was negligible, and plates could be used interchangeably. Uncertainties from other parameters such as source‐to‐surface distance and user variability summed to a combined uncertainty of 0.0003 mm/pixel, compared to a pixel scale range of 0.003 mm/pixel measured across 10 machines. Most of the inter‐machine variation was shown to be attributable to differences in source‐to‐panel distance. Other factors such as focal spot size and shape, electronic portal imager manufacturing consistency, panel sag, and setup errors may account for the residual variation. Individual characterization of machine and imaging panel pixel scale factors is important to ensure accurate geometric information is derived from electronic portal images, which is critical where the portal imager is used for multi‐leaf collimator calibration or other clinical tasks.
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Affiliation(s)
| | - Simon Goodall
- Genesis Care, Perth, Australia.,School of Physics, Mathematics, and Computing, Faculty of Engineering and Mathematical Sciences, University of Western Australia, Crawley, Western Australia, Australia
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Ma Y, Wang X, Mai R, Wang T, Pei Y, Liu S, Guo Y. An electronic portal image device (EPID)-based multiplatform rapid daily LINAC QA tool. J Appl Clin Med Phys 2021; 22:45-58. [PMID: 33410254 PMCID: PMC7856503 DOI: 10.1002/acm2.13055] [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: 10/07/2020] [Revised: 08/07/2020] [Accepted: 09/11/2020] [Indexed: 12/17/2022] Open
Abstract
PURPOSE To develop an efficient and economic daily quality research tool (DQRT) for daily check of multiplatform linear accelerators (LINACs) with flattening filter (FF) and flattening filter-free (FFF) photon beams by using an Electronic Portal Image Device (EPID). MATERIALS AND METHODS After EPID calibration, the monitored parameters were analyzed from a 10 cm × 10 cm open and 60° wedge portal images measured by the EPID with 100 MU exposure. Next, the repeatability of the EPID position accuracy, long-term stability, and linearity between image gray value and exposure were verified. Output and beam quality stability of the 6-MV FF and FFF beams measured by DQRT with the introduced setup errors of EPID were also surveyed. Besides, some test results obtained by DQRT were compared with those measured by FC65-G and Matrixx. At last, the tool was evaluated on three LINACs (Synergy, VersaHD, TrueBeam) for 2 months with two popular commercial QA tools as references. RESULTS There are no differences between repeatability tests for all monitored parameters. Image grayscale values obtained by EPID and exposure show good linearity. Either 6 MV FF or FFF photon beam shows minimal impact to the results. The differences between FC65-G, Matrixx and DQRT results are negligible. Monitor results of the two commercial tools are consistent with the DQRT results collected during the 2-month period. CONCLUSION With a shorter time and procedure, the DQRT is useful to daily QA works of LINACs, producing a QA result quality similarly to or more better than the traditional tools and giving richer contents to the QA results. For hospitals with limited QA time window available or lack of funding to purchase commercial QA tools, the proposed DQRT can provide an alternative and economic approach to accomplish the task of daily QA for LINACs.
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Affiliation(s)
- Yangguang Ma
- Department of Radiation Oncology, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China
| | - Xuemin Wang
- Department of Radiotherapy Hospital Unit Radiation Therapy, Shaanxi Provincial Tumor Hospital, Xi'an, China
| | - Rizhen Mai
- Department of Medical Equipment, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China
| | - Tao Wang
- Department of Radiation Oncology, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China
| | - Yuntong Pei
- Department of Radiation Oncology, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China
| | - Shuaipeng Liu
- Department of Radiation Oncology, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China
| | - Yuexin Guo
- Department of Radiation Oncology, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China
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Slama LA, Riis HL, Sabet M, Barnes MP, Ebert MA, Chan S, Rowshanfarzad P. Beam focal spot intrafraction motion and gantry angle dependence: A study of Varian linac focal spot alignment. Phys Med 2019; 63:41-47. [PMID: 31221407 DOI: 10.1016/j.ejmp.2019.05.021] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/30/2018] [Revised: 05/02/2019] [Accepted: 05/25/2019] [Indexed: 11/25/2022] Open
Abstract
The characteristics of the focal spot of the linear accelerator (linac) play a role in determining the resulting dose distribution within the patient, and hence probability of treatment success. A direct measurement of focal spot position is not recommended by AAPM Task Group 142, but factors influenced by focal spot position, such as beam symmetry and isocentre position, are. Traditional methods of measuring focal spot position are time consuming and can only be performed at gantry 0°. The presented method has been proposed using a phantom of novel design to accurately measure the position of the focal spot relative to the collimator's axis of rotation (CAX) at any gantry angle, and to measure the intra-fraction movement of the focal spot relative to the mean position during treatment. The method was reproducible to within 0.012 mm/0.029 mm (mean/max) for the three Varian linacs tested. The focal spot position was shown to deviate from the CAX by up to 0.386 mm during gantry rotation. The focal spot position was more unstable at the start of treatment, with the worst performing linac having an initial displacement of up to 0.15 mm from its mean position before stabilizing to within 0.01 mm after 3 s. The method proposed is a beneficial addition to the quality assurance (QA) schedule of any clinic, allowing quick determination of source position and movement at any gantry angle. Measurement of focal spot allows the possibility of fine-tuning the electron beam steering system to improve the standard of the photon beam and of stereotactic treatments.
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Affiliation(s)
- Luke A Slama
- Department of Physics, the University of Western Australia, Crawley, WA, Australia; Department of Radiation Oncology, Sir Charles Gairdner Hospital, Nedlands, WA, Australia.
| | - Hans L Riis
- Radiofysisk Laboratorium, Odense University Hospital, DK-5000 Odense C, Denmark
| | - Mahsheed Sabet
- Department of Radiation Oncology, Sir Charles Gairdner Hospital, Nedlands, WA, Australia
| | - Michael P Barnes
- Department of Radiation Oncology, Cavalry Mater Newcastle, Newcastle, NSW, Australia; School of Health Sciences, University of Newcastle, Newcastle, NSW, Australia; School of Mathematical and Physical Sciences, University of Newcastle, Newcastle, NSW, Australia
| | - Martin A Ebert
- Department of Physics, the University of Western Australia, Crawley, WA, Australia; Department of Radiation Oncology, Sir Charles Gairdner Hospital, Nedlands, WA, Australia
| | - Sun Chan
- Department of Medical Technology and Physics, Sir Charles Gairdner Hospital, Nedlands, WA, Australia
| | - Pejman Rowshanfarzad
- Department of Physics, the University of Western Australia, Crawley, WA, Australia
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Riis HL, Ebert MA, Rowshanfarzad P. Detection of the focal spot motion relative to the collimator axis of a linear accelerator under gantry rotation. Phys Med Biol 2019; 64:03NT02. [PMID: 30566917 DOI: 10.1088/1361-6560/aafa04] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The potential for delivering high precision radiotherapy using linear accelerators (linacs) has been improved with the development of digital x-ray electronic portal imaging devices (EPID) for acquiring kilovoltage (kV) cone-beam CT and megavoltage (MV) images for patient positioning. EPIDs have also opened the possibilities of developing novel quality assurance and insight into radiotherapy equipment performance. The aim of this work was to measure the offset of the focal spot position (FSP) of a linac under gantry rotation relative to the collimator axis using an EPID. The focal spot was assumed to be a point source of MV x-ray generation. A special phantom was designed for measurement of FSP as a function of gantry angle on clinical linacs. The phantom was designed for attachment to the gantry head and supporting two tungsten-carbide ball-bearings at two different distances from the focal spot. The methodology was demonstrated on a series of images acquired of the phantom on three Elekta linacs in clinical use with 6 MV flattening-filter-free (FFF) beams. The gantry and collimator were rotated 360° in steps of 30°. For each position an image of the phantom was acquired using the EPID. Each series consisted of 169 EPID images. The images were analysed using in-house developed software. Analyses of the EPID images acquired with 6 MV FFF beams showed that the focal spot motion amplitudes relative to the collimator axis during gantry rotation in the longitudinal and lateral directions were less than 0.10 mm and 0.50 mm, respectively, for an optimized 6 MV FFF FSP calibrated linac. In a treatment planning system (TPS) the focal spot is assumed to be located on the rotation axis of the collimator at all gantry angles. This work introduces a method for quantifying the actual variation from this assumption in practice.
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Affiliation(s)
- Hans L Riis
- Radiofysisk Laboratorium, Odense University Hospital, DK-5000 Odense C, Denmark. Author to whom any correspondence should be addressed
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Gourdeau D, Gingras L, Beaulieu F, Leclerc G, Archambault L. An EPID-based method to determine mechanical deformations in a linear accelerator. Med Phys 2018; 45:5054-5065. [PMID: 30242848 DOI: 10.1002/mp.13184] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2017] [Revised: 07/19/2018] [Accepted: 09/05/2018] [Indexed: 11/12/2022] Open
Abstract
PURPOSE Medical linear accelerators (linac) are delivering increasingly complex treatments using modern techniques in radiation therapy. Complete and precise mechanical QA of the linac is therefore necessary to ensure that there is no unexpected deviation from the gantry's planned course. However, state-of-the-art EPID-based mechanical QA procedures often neglect some degrees of freedom (DOF) like the in-plane rotations of the gantry and imager or the source movements inside the gantry head. Therefore, the purpose of this work is to characterize a 14 DOF method for the mechanical QA of linacs. This method seeks to measure every mechanical deformation in a linac, including source movements, in addition to relevant clinical parameters like mechanical and radiation isocenters. METHODS A widely available commercial phantom and a custom-made accessory inserted in the linac's interface mount are imaged using the electronic portal imaging device (EPID) at multiple gantry angles. Then, simulated images are generated using the nominal geometry of the linac and digitized models of the phantoms. The nominal geometry used to generate these images can be modified using 14 DOF (3 rigid rotations and 3 translations for the imager and the gantry, and 2 in-plane translations of the source) and any change will modify the simulated image. The set of mechanical deformations that minimizes the differences between the simulated and measured image is found using a genetic algorithm coupled with a gradient-descent optimizer. Phantom mispositioning and gantry angular offset were subsequently calculated and extracted from the results. Simulations of the performances of the method for different levels of noise in the phantom models were performed to calculate the absolute uncertainty of the measured mechanical deformations. The measured source positions and the center of collimation were used to define the beam central axis and calculate the radiation isocenter position and radius. RESULTS After the simultaneous optimization of the 14 DOF, the average distance between the center of the measured and simulated ball bearings on the imager was 0.086 mm. Over the course of a full counter-clockwise gantry rotation, all mechanical deformations were measured, showing sub-millimeter translations and rotations smaller than 1° along every axis. The average absolute uncertainty of the 14 DOF (1 SD) was 0.15 mm or degree. Phantom positioning errors were determined with more than 0.1 mm precision. Errors introduced in the experimental setup like phantom positioning errors, source movements or gantry angular offsets were all successfully detected by our QA method. The mechanical deformations measured are shown to be reproducible over the course of a few weeks and are not sensitive to the experimental setup. CONCLUSION This work presents of new method for an accurate mechanical QA of the linacs. It features a 14 DOF model of the mechanical deformations that is both more complete and precise than other available methods. It has demonstrated sub-millimeter accuracy through simulation and experimentation. Introduced errors were successfully detected with high precision.
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Affiliation(s)
- Daniel Gourdeau
- Département de Radio-Oncologie, CHU de Québec, 11 Côte du Palais, Québec, QC, Canada, G1R 0A2.,Département de Physique, de Génie physique et d'Optique, Université Laval, 2325 rue de l' Université, Québec, QC, Canada, G1V 0A6
| | - Luc Gingras
- Département de Radio-Oncologie, CHU de Québec, 11 Côte du Palais, Québec, QC, Canada, G1R 0A2
| | - Frédéric Beaulieu
- Département de Radio-Oncologie, CHU de Québec, 11 Côte du Palais, Québec, QC, Canada, G1R 0A2
| | - Ghyslain Leclerc
- Département de Radio-Oncologie, CHU de Québec, 11 Côte du Palais, Québec, QC, Canada, G1R 0A2
| | - Louis Archambault
- Département de Radio-Oncologie, CHU de Québec, 11 Côte du Palais, Québec, QC, Canada, G1R 0A2.,Département de Physique, de Génie physique et d'Optique, Université Laval, 2325 rue de l' Université, Québec, QC, Canada, G1V 0A6
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Barnes MP, Menk FW, Lamichhane BP, Greer PB. A proposed method for linear accelerator photon beam steering using EPID. J Appl Clin Med Phys 2018; 19:591-597. [PMID: 30047209 PMCID: PMC6123104 DOI: 10.1002/acm2.12419] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2018] [Revised: 05/11/2018] [Accepted: 06/29/2018] [Indexed: 11/30/2022] Open
Abstract
Beam steering is the process of calibrating the angle and translational position with which a linear accelerator's (linac's) electron beam strikes the x‐ray target with respect to the collimator rotation axis. The shape of the dose profile is highly dependent on accurate beam steering and is essential for ensuring correct delivery of the radiotherapy treatment plan. Traditional methods of beam steering utilize a scanning water tank phantom that makes the process user‐dependent. This study is the first to provide a methodology for both beam angle steering and beam translational position steering based on EPID imaging of the beam and does not require a phantom. Both the EPID‐based beam angle steering and beam translational steering methods described have been validated against IC Profiler measurement. Wide field symmetry agreement was found between the EPID and IC Profiler to within 0.06 ± 0.14% (1 SD) and 0.32 ± 0.11% (1 SD) for flattened and flattening‐filter‐free (FFF) beams, respectively. For a 1.1% change in symmetry measured by IC Profiler the EPID method agreed to within 0.23%. For beam translational position steering, the EPID method agreed with IC Profiler method to within 0.03 ± 0.05 mm (1 SD) at isocenter. The EPID‐based methods presented are quick to perform, simple, accurate and could easily be integrated with the linac, potentially via the MPC application. The methods have the potential to remove user variability and to standardize the process of beam steering throughout the radiotherapy community.
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Affiliation(s)
- Michael P Barnes
- Department of Radiation Oncology, Calvary Mater Hospital Newcastle, NSW, Australia.,School of Medical Radiation Sciences, University of Newcastle, Newcastle, NSW, Australia.,School of Mathematical and Physical Sciences, University of Newcastle, Newcastle, NSW, Australia
| | - Frederick W Menk
- School of Mathematical and Physical Sciences, University of Newcastle, Newcastle, NSW, Australia
| | - Bishnu P Lamichhane
- School of Mathematical and Physical Sciences, University of Newcastle, Newcastle, NSW, Australia
| | - Peter B Greer
- Department of Radiation Oncology, Calvary Mater Hospital Newcastle, NSW, Australia.,School of Mathematical and Physical Sciences, University of Newcastle, Newcastle, NSW, Australia
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Chojnowski JM, Taylor LM, Sykes JR, Thwaites DI. Beam focal spot position determination for an Elekta linac with the Agility ® head; practical guide with a ready-to-go procedure. J Appl Clin Med Phys 2018; 19:44-47. [PMID: 29761625 PMCID: PMC6036348 DOI: 10.1002/acm2.12344] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2017] [Revised: 03/08/2018] [Accepted: 03/12/2018] [Indexed: 11/17/2022] Open
Abstract
A novel phantomless, EPID‐based method of measuring the beam focal spot offset of a linear accelerator was proposed and validated for Varian machines. In this method, one set of jaws and the MLC were utilized to form a symmetric field and then a 180o collimator rotation was utilized to determine the radiation isocenter defined by the jaws and the MLC, respectively. The difference between these two isocentres is directly correlated with the beam focal spot offset of the linear accelerator. In the current work, the method has been considered for Elekta linacs. An Elekta linac with the Agility® head does not have two set of jaws, therefore, a modified method is presented making use of one set of diaphragms, the MLC and a full 360o collimator rotation. The modified method has been tested on two Elekta Synergy® linacs with Agility® heads and independently validated. A practical guide with instructions and a MATLAB® code is attached for easy implementation.
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Affiliation(s)
- Jacek M Chojnowski
- Mid North Coast Cancer Institute, Coffs Harbour Health Campus, Coffs Harbour, NSW, Australia.,Institute of Medical Physics, School of Physics, University of Sydney, Sydney, NSW, Australia
| | - Lee M Taylor
- Mid North Coast Cancer Institute, Coffs Harbour Health Campus, Coffs Harbour, NSW, Australia
| | - Jonathan R Sykes
- Institute of Medical Physics, School of Physics, University of Sydney, Sydney, NSW, Australia.,Department of Radiation Oncology, Blacktown Cancer & Haematology Centre, Blacktown, NSW, Australia
| | - David I Thwaites
- Institute of Medical Physics, School of Physics, University of Sydney, Sydney, NSW, Australia
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