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Hayes C, King RB, Hounsell AR, Agnew CE. Impact of target degradation on the 6FFF output of a Varian TrueBeam Linac. Phys Med 2024; 124:103424. [PMID: 39002424 DOI: 10.1016/j.ejmp.2024.103424] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/04/2024] [Revised: 06/07/2024] [Accepted: 06/29/2024] [Indexed: 07/15/2024] Open
Abstract
The dosimetric output of a 6FFF beam, produced from a Varian TrueBeam linac exhibited an unexpected downward trend over time that was contrary to well-established expectations. To elucidate the cause of this uncharacteristic trend, a review of the linac's quality control results over its lifetime was performed, including, constancy checks of the dosimetric output, beam energy, flatness and symmetry, and percentage depth dose characteristics. These results were supplemented with a comprehensive series of measurements including flatness and symmetry measurements with a 1D-diode array, high-resolution measurements of the photon beam's build-up region with a parallel-plate chamber and measurement of the beam's output as a function of the x-ray target position. The review of the linac's QC results and supplemental tests identified no deviations in the linac's performance from its commissioning and baseline measurements. However, the 6FFF beam output exhibited a significant dependence on the target location relative to its default position, increasing by 5.43 % with a 0.5 mm target translation, indicating that target degradation was the cause of the atypical output trend. The change in output behaviour was believed to be the result of primary electrons escaping the degraded target and interacting with the linac's monitor chamber. Replacement of the x-ray target caused the 6FFF output to realign with expected trends. Target degradation was uncovered due to a robust quality control trending database and awareness of typical output behaviour. These results demonstrate the importance of data trending to identify component failure and provide centres with knowledge to recognise this potential fault.
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Affiliation(s)
- Chris Hayes
- Radiotherapy Physics, Northern Ireland Cancer Centre, Belfast City Hospital, Belfast, Northern Ireland, United Kingdom.
| | - Raymond B King
- Radiotherapy Physics, Northern Ireland Cancer Centre, Belfast City Hospital, Belfast, Northern Ireland, United Kingdom
| | - Alan R Hounsell
- Radiotherapy Physics, Northern Ireland Cancer Centre, Belfast City Hospital, Belfast, Northern Ireland, United Kingdom; Patrick G Johnston Centre for Cancer Research, Queen's University Belfast, Jubilee Road, Belfast, Northern Ireland, United Kingdom
| | - Christina E Agnew
- Radiotherapy Physics, Northern Ireland Cancer Centre, Belfast City Hospital, Belfast, Northern Ireland, United Kingdom
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Srivastava SP, Sorensen SP, Jani SS, Yan X, Pinnaduwage DS. Machine performance and stability of the first clinical self-shielded stereotactic radiosurgery system: Initial 2-year experience. J Appl Clin Med Phys 2023; 24:e13857. [PMID: 36519493 PMCID: PMC10018673 DOI: 10.1002/acm2.13857] [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: 07/08/2022] [Revised: 11/04/2022] [Accepted: 11/08/2022] [Indexed: 12/23/2022] Open
Abstract
This study provides insight into the overall system performance, stability, and delivery accuracy of the first clinical self-shielded stereotactic radiosurgery (SRS) system. Quality assurance procedures specifically developed for this unit are discussed, and trends and variations over the course of 2-years for beam constancy, targeting and dose delivery are presented. Absolute dose calibration for this 2.7 MV unit is performed to deliver 1 cGy/MU at dmax = 7 mm at a source-to-axis-distance (SAD) of 450 mm for a 25 mm collimator. Output measurements were made with 2-setups: a device that attaches to a fixed position on the couch (daily) and a spherical phantom that attaches to the collimating wheel (monthly). Beam energy was measured using a cylindrical acrylic phantom at depths of 100 (D10 ) and 200 (D20 ) mm. Beam profiles were evaluated using Gafchromic film and compared with TPS beam data. Accuracy in beam targeting was quantified with the Winston-Lutz (WL) and end-to-end (E2E) tests. Delivery quality assurance (DQA) was performed prior to clinical treatments using Gafchromic EBT3/XD film. Net cumulative output adjustments of 15% (pre-clinical), 9% (1st year) and 3% (2nd year) were made. The mean output was 0.997 ± 0.010 cGy/MU (range: 0.960-1.046 cGy/MU) and 0.993 ± 0.029 cGy/MU (range: 0.884-1.065 cGy/MU) for measurements with the daily and monthly setups, respectively. The mean relative beam energy (D10 /D20 ) was 0.998 ± 0.004 (range: 0.991-1.006). The mean total targeting error was 0.46 ± 0.17 mm (range: 0.06-0.98 mm) for the WL and 0.52 ± 0.28 mm (range: 0.11-1.27 mm) for the E2E tests. The average gamma pass rates for DQA measurements were 99.0% and 90.5% for 2%/2 mm and 2%/1 mm gamma criteria, respectively. This SRS unit meets tolerance limits recommended by TG-135, MPPG 9a., and TG-142 with a treatment delivery accuracy similar to what is achieved by other SRS systems.
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Affiliation(s)
- Shiv P Srivastava
- Department of Radiation Oncology, St. Joseph's Hospital and Medical Center, Phoenix, AZ, USA
| | - Stephen P Sorensen
- Department of Radiation Oncology, St. Joseph's Hospital and Medical Center, Phoenix, AZ, USA
| | - Shyam S Jani
- Department of Radiation Oncology, St. Joseph's Hospital and Medical Center, Phoenix, AZ, USA
| | - Xiangsheng Yan
- Department of Radiation Oncology, St. Joseph's Hospital and Medical Center, Phoenix, AZ, USA
| | - Dilini S Pinnaduwage
- Department of Radiation Oncology, St. Joseph's Hospital and Medical Center, Phoenix, AZ, USA
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Takagi M, Narita Y, Chai H, Kimura T, Soda K, Kattou K. Correcting for the effect of ambient pressure fluctuations on measured output from a linear accelerator with a sealed monitor chamber. Biomed Phys Eng Express 2023; 9. [PMID: 36689771 DOI: 10.1088/2057-1976/acb554] [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: 10/27/2022] [Accepted: 01/23/2023] [Indexed: 01/24/2023]
Abstract
Objective.Ambient pressure fluctuations deform the walls of a sealed monitor chamber in a linear accelerator (LINAC) and affect the output. This study retrospectively quantified the output variations accompanying ambient pressure fluctuations in a LINAC equipped with a sealed monitor chamber and introduced a novel approach of calculating the adjusted output free from the effect of ambient pressure fluctuations.Approach.The output data for the 6 MV and 10 MV X-rays measured between March 2014 and September 2015 were analysed. This period was further divided into four sub-periods according to the output calibrations. Output behaviours were modelled using multiple regression analysis with ambient pressure and the time elapsed since the last calibration as explanatory variables. The output variations accompanying ambient pressure fluctuations were calculated using regression parameters and were subtracted from the measured outputs to obtain the adjusted outputs.Main results.The partial regression coefficients for ambient pressure varied from -2.3 × 10-4to -1.8 × 10-4cGy/MU/hPa for 6 MV and from -1.9 × 10-4to -1.2 × 10-4cGy/MU/hPa for 10 MV X-rays. These partial regression coefficient values were comparable among the four sub-periods and the two x-ray energies, respectively. These findings suggest that the degree of the output variations accompanying ambient pressure fluctuations is independent of x-ray energies and is determined by the internal structure of the chamber and the pressure differential between the inside and outside of the chamber. The adjusted outputs showed a better fit with the time trend line than the measured outputs.Significance.This study demonstrates a novel procedure for obtaining the adjusted outputs and allows precise observation of the output behaviours of a LINAC equipped with a sealed monitor chamber. Combined observation of the measured and adjusted output facilitates the detection of output anomalies, thus contributing to quality control (QC) of LINACs.
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Affiliation(s)
- Masafumi Takagi
- Division of Radiology, Hirosaki Central Hospital, 3-1 Yoshino-Cho Hirosaki, Aomori 036-8188, Japan
| | - Yuichiro Narita
- Section of Medical Physics, Aomori Shintoshi Hospital, 3-1 Ishie, Aomori city, Aomori 038-0003, Japan
| | - Hongbo Chai
- Division of Radiology, Hirosaki Central Hospital, 3-1 Yoshino-Cho Hirosaki, Aomori 036-8188, Japan
| | - Tomomi Kimura
- Division of Radiology, Hirosaki Central Hospital, 3-1 Yoshino-Cho Hirosaki, Aomori 036-8188, Japan
| | - Kenji Soda
- Division of Radiology, Hirosaki Central Hospital, 3-1 Yoshino-Cho Hirosaki, Aomori 036-8188, Japan
| | - Keiichi Kattou
- Division of Radiology, Hirosaki Central Hospital, 3-1 Yoshino-Cho Hirosaki, Aomori 036-8188, Japan
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Cetnar AJ, DiCostanzo DJ. The lifetime of a linac monitor unit ion chamber. J Appl Clin Med Phys 2021; 22:108-114. [PMID: 34762336 PMCID: PMC8664141 DOI: 10.1002/acm2.13463] [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: 05/05/2021] [Revised: 09/16/2021] [Accepted: 10/07/2021] [Indexed: 11/22/2022] Open
Abstract
This study is the first to report the clinical lifetime of Varian Kapton sealed ion chambers as a retrospective review. The data have been analyzed using ion chamber gain values, daily quality assurance results, monthly quality assurance results, and delivered treatment field data were analyzed to comprehensively review trends. The data show the average lifetimes of the ion chambers from our institution, so other physicists can prepare for replacement. Additionally, we share our experience in performing quality assurance tests to calibrate and validate the radiation beam after ion chamber replacement.
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Affiliation(s)
- Ashley J Cetnar
- Department of Radiation Oncology, The Ohio State University, Columbus, Ohio, USA
| | - Dominic J DiCostanzo
- Department of Radiation Oncology, The Ohio State University, Columbus, Ohio, USA
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Bolt M, Clark CH, Nisbet A, Chen T. Quantification of the uncertainties within the radiotherapy dosimetry chain and their impact on tumour control. Phys Imaging Radiat Oncol 2021; 19:33-38. [PMID: 34307916 PMCID: PMC8295844 DOI: 10.1016/j.phro.2021.06.004] [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: 11/14/2020] [Revised: 06/17/2021] [Accepted: 06/21/2021] [Indexed: 11/25/2022] Open
Abstract
BACKGROUND AND PURPOSE Dose delivered during radiotherapy has uncertainty arising from a number of sources including machine calibration, treatment planning and delivery and can impact outcomes. Any systematic uncertainties will impact all patients and can continue for extended periods. The impact on tumour control probability (TCP) of the uncertainties within the radiotherapy calibration process has been assessed. MATERIALS AND METHODS The linear-quadratic model was used to simulate the TCP from two prostate cancer and a head and neck (H&N) clinical trial. The uncertainty was separated into four components; 1) initial calibration, 2) systematic shift due to output drift, 3) drift during treatment and 4) daily fluctuations. Simulations were performed for each clinical case to model the variation in TCP present at the end of treatment arising from the different components. RESULTS Overall uncertainty in delivered dose was +/-2.1% (95% confidence interval (CI)), consisting of uncertainty standard deviations of 0.7% in initial calibration, 0.8% due to subsequent calibration shift due to output drift, 0.1% due to drift during treatment, and 0.2% from daily variations. The overall uncertainty of TCP (95% CI) for a population of patients treated on different machines was +/-3%, +/-5%, and +/-3% for simulations based on the two prostate trials and H&N trial respectively. CONCLUSION The greatest variation in delivered target volume dose arose from calibration shift due to output drift. Careful monitoring of beam output following initial calibration remains vital and may have a significant impact on clinical outcomes.
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Affiliation(s)
- Matthew Bolt
- Department of Medical Physics, St Luke’s Cancer Centre, Royal Surrey County Hospital NHS Foundation Trust, Guildford, UK
- National Physical Laboratory, Teddington, UK
- Department of Chemical and Process Engineering, University of Surrey, Guildford, UK
| | - Catharine H. Clark
- National Physical Laboratory, Teddington, UK
- Radiotherapy Physics, University College London Hospital NHS Foundation Trust, London, UK
| | - Andrew Nisbet
- Department of Medical Physics and Biomedical Engineering, University College London, London, UK
| | - Tao Chen
- Department of Chemical and Process Engineering, University of Surrey, Guildford, UK
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Pearson M, Eaton D, Greener T. Long-term experience of MPC across multiple TrueBeam linacs: MPC concordance with conventional QC and sensitivity to real-world faults. J Appl Clin Med Phys 2020; 21:224-235. [PMID: 32790139 PMCID: PMC7484877 DOI: 10.1002/acm2.12950] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2020] [Revised: 05/11/2020] [Accepted: 05/16/2020] [Indexed: 11/12/2022] Open
Abstract
Machine Performance Check (MPC) is an automated Quality Control (QC) tool that is integrated into the TrueBeam and Halcyon linear accelerators (Linacs), utilizing the imaging systems to verify the Linac beam and geometry. This work compares the concordance of daily MPC results with conventional QC tests over a 3-year period for eight Linacs in order to assess the sensitivity of MPC in detecting faults. The MPC output measurements were compared with the monthly ionization chamber measurements for 6 and 10 MV photon beams and 6, 9, 12, 16, and 18 MeV electron beams. All 6 MV Beam and Geometry (6MVBG) MPC test failures were analyzed to determine the failure rate and the number of true and false negative results, using the conventional QC record as the reference. The concordance between conventional QC test failures and MPC test failures was investigated. The mean agreement across 1933 MPC output and monthly comparison chamber measurements for all beam energies was 0.2%, with 97.8% within 1.5%, and a maximum difference of 2.9%. Of the 5000-6000 MPC individual test parameter results for the 6MVBG test, the highest failure rate was BeamOutputChange (0.5%), then BeamCenterShift (0.3%), and was ≤ 0.1% for the remaining parameters. There were 50 true negative and 27 false negative out of tolerance MPC results, with false negatives resolved by repeating MPC or by independent measurement. The analysis of conventional QC failures demonstrated that MPC detected all failures, except occasions when MPC reported output within tolerance, a result of the MPC-chamber response variation. The variation in MPC output versus chamber measurement indicates MPC is appropriate for daily output constancy but not for the measurement of absolute output. The comparison of the 6MVBG results and conventional records provides evidence that MPC is a sensitive method of performing beam and mechanical checks in a clinical setting.
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Affiliation(s)
- Michael Pearson
- Medical Physics Department, Guys and St Thomas' Hospital, London, SE1 9RT, United Kingdom
| | - David Eaton
- Medical Physics Department, Guys and St Thomas' Hospital, London, SE1 9RT, United Kingdom
| | - Tony Greener
- Medical Physics Department, Guys and St Thomas' Hospital, London, SE1 9RT, United Kingdom
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McCaw TJ, Barraclough BA, Belanger M, Besemer A, Dunkerley DAP, Labby ZE. Diagnosing atmospheric communication of a sealed monitor chamber. J Appl Clin Med Phys 2020; 21:309-314. [PMID: 32648368 PMCID: PMC7484838 DOI: 10.1002/acm2.12975] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2019] [Revised: 06/12/2020] [Accepted: 06/18/2020] [Indexed: 11/10/2022] Open
Affiliation(s)
- Travis J. McCaw
- Department of Human Oncology University of Wisconsin Madison WI USA
| | | | - Maxwell Belanger
- Department of Human Oncology University of Wisconsin Madison WI USA
| | - Abigail Besemer
- Department of Radiation Oncology University of Nebraska Medical Center Omaha NE USA
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Matsumoto K, Tarutani K. [Characteristics of Monitor Chamber for Photon Energy Mounted on Linear Accelerators]. Nihon Hoshasen Gijutsu Gakkai Zasshi 2019; 75:1135-1140. [PMID: 31631106 DOI: 10.6009/jjrt.2019_jsrt_75.10.1135] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Radiotherapy linear accelerators are calibrated to deliver a specific dose under standard conditions following accepted protocols (for example, JSMP12 protocol). The linear accelerator output is calibrated to deliver 1.0 cGy per 1.0 monitor unit (MU) at the depth of maximum in tissue maximum ratio. Beams of photons or electrons pass through a monitor chamber located in the linear accelerators head, which turns off the beam once the prescribed MU is delivered. The clinical outcome of radiotherapy demands that the linear accelerators output do not deviate from the calibrated level by more than a few percent. The purpose of this study is to characterize and understand the long term behavior of the output, change of flatness and symmetry from megavoltage radiotherapy linear accelerators (TrueBeam, Varian Medical Systems). Output trends of beams from three linear accelerators in two institutions over a period of more than 3 years are reported and analyzed. Output taken once per month the basis of this study. The output is measured using ionization chamber with water phantom. These are calibrated by accredited dosimetry laboratory with Japanese traceability system. When the output variation was bounded ±1%, monitor chamber was re-calibrated. The results show that the output from Linac was constantly upward trend. The output of Linac increased up to 8.0% in 1st year. However, upward trend became plateau slowly after years. Beams of same energies from another Linac are correlated with a correlation coefficient. Symmetry and flatness from one Truebeam stabled within 1%. If these adjustments are artificially removed then there is an increase in output, it is important to check the output of linear accelerator periodically.
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Ochi Y, Saito A, Kawahara D, Suzuki T, Tsuneda M, Tanaka S, Nishio T, Ozawa S, Murakami Y, Nagata Y. A novel risk analysis of clinical reference dosimetry based on failure modes and effects analysis. Phys Med 2019; 58:59-65. [PMID: 30824151 DOI: 10.1016/j.ejmp.2019.01.014] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/02/2018] [Revised: 12/29/2018] [Accepted: 01/22/2019] [Indexed: 10/27/2022] Open
Abstract
PURPOSE The output of a linear accelerator (linac) is one of the most important quality assurance (QA) factors in radiotherapy. However, there is no quantitative rationale for frequency and tolerance. The purpose of this study is to develop a novel risk analysis of clinical reference dosimetry based on failure modes and effects analysis (FMEA). METHODS Clinical reference dosimetry data and the daily output data of two linacs (Clinac iX and Clinac 6EX) at Hiroshima University Hospital were analyzed. The analysis involved the number of patients per year for five types of fractionations. Risk priority number (RPN) is defined as the product of occurrence (O), severity (S), and detectability (D) in standard FMEA. In addition, we introduced "severity due to output drifting" (mean output change per day) (S') and the number of patients per year for five types of fractionations (W). We calculated the RPN = O × S × D × S' × W and quantitatively evaluated the risk for clinical reference dosimetry. RESULTS Fewer fractions and less output calibration frequency resulted in higher RPN. Since clinical reference dosimetry data has a drift effect, which is missing in human processes, it was essential to use S' in addition to standard FMEA. Moreover, the parameter W was important in evaluating interinstitutional QA for clinical reference dosimetry. The relative risk of Clinac 6EX to Clinac iX was different approximately by twofold. CONCLUSIONS We developed a novel index that can quantitatively evaluate risk for clinical reference dosimetry of each facility and machines in common on the basis of FMEA.
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Affiliation(s)
- Yusuke Ochi
- Radiation Therapy Section, Department of Clinical Support, Hiroshima University Hospital, Hiroshima 734-8551, Japan; Department of Radiation Oncology, Graduate School of Biomedical & Health Sciences, Hiroshima University, Hiroshima 734-8551, Japan
| | - Akito Saito
- Department of Radiation Oncology, Hiroshima University Hospital, Hiroshima 734-8551, Japan.
| | - Daisuke Kawahara
- Radiation Therapy Section, Department of Clinical Support, Hiroshima University Hospital, Hiroshima 734-8551, Japan; Department of Radiation Oncology, Graduate School of Biomedical & Health Sciences, Hiroshima University, Hiroshima 734-8551, Japan
| | - Tatsuhiko Suzuki
- Department of Radiation Oncology, Graduate School of Biomedical & Health Sciences, Hiroshima University, Hiroshima 734-8551, Japan
| | - Masato Tsuneda
- Department of Radiation Oncology, Graduate School of Biomedical & Health Sciences, Hiroshima University, Hiroshima 734-8551, Japan; Department of Radiation Oncology, Tokyo Women's Medical University, Tokyo 162-8666, Japan
| | - Sodai Tanaka
- Department of Nuclear Engineering and Management, School of Engineering, University of Tokyo, Tokyo 113-8656, Japan
| | - Teiji Nishio
- Department of Medical Physics, Graduate School of Medical Science, Tokyo Women's Medical University, Tokyo 162-8666, Japan
| | - Shuichi Ozawa
- Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima 732-0057, Japan; Department of Radiation Oncology, Institute of Biomedical and Health Sciences, Hiroshima University, Japan
| | - Yuji Murakami
- Department of Radiation Oncology, Institute of Biomedical and Health Sciences, Hiroshima University, Japan
| | - Yasushi Nagata
- Department of Radiation Oncology, Institute of Biomedical and Health Sciences, Hiroshima University, Japan
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Bartolac S, Heaton R, Norrlinger B, Letourneau D. Seasonal variations in measurements of linear accelerator output. J Appl Clin Med Phys 2019; 20:81-88. [PMID: 30817079 PMCID: PMC6414147 DOI: 10.1002/acm2.12548] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2018] [Revised: 09/05/2018] [Accepted: 11/14/2018] [Indexed: 11/10/2022] Open
Abstract
PURPOSE Seasonal trends in linear accelerator output have been reported by at least one institution and data have suggested that they may be present at our center as well. The purpose of this work was to characterize these trends and determine whether local environmental conditions within the treatment rooms may be impacting the linear accelerators and/or the quality control (QC) dosimeter. METHODS Runtime plots of daily output data, acquired using an in-house ion chamber-based device, over 3 yr and for 15 linear accelerators of different makes and models were reviewed and evaluated. Environmental conditions were monitored prospectively in a representative treatment room for approximately 9 months and evaluated for correlations with output trends. Independent measures of output using daily MV portal images were compared with output measurements using the ion chamber-based device. A separate controlled experiment probing the response of the in-house dosimeter to humidity changes over time was also carried out using a constant current source and a small enclosure. RESULTS Runtime plots of output revealed sinusoidal, seasonal variations that were consistent across all treatment units, irrespective of manufacturer, model, or age of machine. The amplitude of the variation was on the order of 1% and maintained a yearly period. The independent measure of output using MV portal images did not corroborate the seasonal trends observed with the daily QC dosimeter. Based on the controlled experiment, the QC dosimeter was found to have a dependence on relative humidity changes, decreasing 1% in output per 30% increase in relative humidity. CONCLUSIONS Results confirm the presence of underlying seasonal variations in measured output from the linear accelerators. The findings identify humidity impact on the measurement device as the underlying cause of the cyclical changes and not the accelerators themselves. These results could help minimize unwarranted machine servicing.
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Affiliation(s)
- Steven Bartolac
- Radiation Medicine Program, Princess Margaret Cancer Center, Toronto, ON, Canada.,Radiation Oncology, Johns Hopkins School of Medicine, Baltimore, MD, USA
| | - Robert Heaton
- Radiation Medicine Program, Princess Margaret Cancer Center, Toronto, ON, Canada
| | - Bernhard Norrlinger
- Radiation Medicine Program, Princess Margaret Cancer Center, Toronto, ON, Canada
| | - Daniel Letourneau
- Radiation Medicine Program, Princess Margaret Cancer Center, Toronto, ON, Canada
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11
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Bolt MA, Clark CH, Chen T, Nisbet A. A multi-centre analysis of radiotherapy beam output measurement. Phys Imaging Radiat Oncol 2017. [DOI: 10.1016/j.phro.2017.12.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022] Open
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12
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Binny D, Lancaster CM, Kairn T, Trapp JV, Crowe SB. Monitoring Daily QA 3 constancy for routine quality assurance on linear accelerators. Phys Med 2016; 32:1479-1487. [DOI: 10.1016/j.ejmp.2016.10.021] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/13/2016] [Revised: 09/21/2016] [Accepted: 10/24/2016] [Indexed: 10/20/2022] Open
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13
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Li Q, Chan MF. Predictive time-series modeling using artificial neural networks for Linac beam symmetry: an empirical study. Ann N Y Acad Sci 2016; 1387:84-94. [PMID: 27627049 DOI: 10.1111/nyas.13215] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Over half of cancer patients receive radiotherapy (RT) as partial or full cancer treatment. Daily quality assurance (QA) of RT in cancer treatment closely monitors the performance of the medical linear accelerator (Linac) and is critical for continuous improvement of patient safety and quality of care. Cumulative longitudinal QA measurements are valuable for understanding the behavior of the Linac and allow physicists to identify trends in the output and take preventive actions. In this study, artificial neural networks (ANNs) and autoregressive moving average (ARMA) time-series prediction modeling techniques were both applied to 5-year daily Linac QA data. Verification tests and other evaluations were then performed for all models. Preliminary results showed that ANN time-series predictive modeling has more advantages over ARMA techniques for accurate and effective applicability in the dosimetry and QA field.
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Affiliation(s)
- Qiongge Li
- Department of Physics, The Graduate Center of the City University of New York, New York, New York.,Department of Physics, The City College of New York, New York, New York
| | - Maria F Chan
- Department of Medical Physics, Memorial Sloan Kettering Cancer Center, Basking Ridge, New Jersey
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Chan MF, Li Q, Tang X, Li X, Li J, Tang G, Hunt MA, Deasy JO. Visual Analysis of the Daily QA Results of Photon and Electron Beams of a Trilogy Linac over a Five-year Period. INTERNATIONAL JOURNAL OF MEDICAL PHYSICS, CLINICAL ENGINEERING AND RADIATION ONCOLOGY 2015; 4:290-299. [PMID: 27547595 PMCID: PMC4989913 DOI: 10.4236/ijmpcero.2015.44035] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Data visualization technique was applied to analyze the daily QA results of photon and electron beams. Special attention was paid to any trend the beams might display. A Varian Trilogy Linac equipped with dual photon energies and five electron energies was commissioned in early 2010. Daily Linac QA tests including the output constancy, beam flatness and symmetry (radial and transverse directions) were performed with an ionization chamber array device (QA BeamChecker Plus, Standard Imaging). The data of five years were collected and analyzed. For each energy, the measured data were exported and processed for visual trending using an in-house Matlab program. These daily data were cross-correlated with the monthly QA and annual QA results, as well as the preventive maintenance records. Majority of the output were within 1% of variation, with a consistent positive/upward drift for all seven energies (~+0.25% per month). The baseline of daily device is reset annually right after the TG-51 calibration. This results in a sudden drop of the output. On the other hand, the large amount of data using the same baseline exhibits a sinusoidal behavior (cycle = 12 months; amplitude = 0.8%, 0.5% for photons, electrons, respectively) on symmetry and flatness when normalization of baselines is accounted for. The well known phenomenon of new Linac output drift was clearly displayed. This output drift was a result of the air leakage of the over-pressurized sealed monitor chambers for the specific vendor. Data visualization is a new trend in the era of big data in radiation oncology research. It allows the data to be displayed visually and therefore more intuitive. Based on the visual display from the past, the physicist might predict the trend of the Linac and take actions proactively. It also makes comparisons, alerts failures, and potentially identifies causalities.
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Affiliation(s)
- Maria F. Chan
- Dept. of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, NY
| | - Qiongge Li
- Dept. of Physics, The City University of New York, New York, NY
| | - Xiaoli Tang
- Dept. of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, NY
| | - Xiang Li
- Dept. of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, NY
| | - Jingdong Li
- Dept. of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, NY
| | - Grace Tang
- Dept. of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, NY
| | - Margie A. Hunt
- Dept. of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, NY
| | - Joseph O. Deasy
- Dept. of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, NY
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Hossain M. Output trends, characteristics, and measurements of three megavoltage radiotherapy linear accelerators. J Appl Clin Med Phys 2014; 15:4783. [PMID: 25207404 PMCID: PMC4393854 DOI: 10.1120/jacmp.v15i4.4783] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2013] [Revised: 03/24/2014] [Accepted: 03/12/2014] [Indexed: 11/26/2022] Open
Abstract
The purpose of this study is to characterize and understand the long‐term behavior of the output from megavoltage radiotherapy linear accelerators. Output trends of nine beams from three linear accelerators over a period of more than three years are reported and analyzed. Output, taken during daily warm‐up, forms the basis of this study. The output is measured using devices having ion chambers. These are not calibrated by accredited dosimetry laboratory, but are baseline‐compared against monthly output which is measured using calibrated ion chambers. We consider the output from the daily check devices as it is, and sometimes normalized it by the actual output measured during the monthly calibration of the linacs. The data show noisy quasi‐periodic behavior. The output variation, if normalized by monthly measured “real’ output, is bounded between ± 3%. Beams of different energies from the same linac are correlated with a correlation coefficient as high as 0.97, for one particular linac, and as low as 0.44 for another. These maximum and minimum correlations drop to 0.78 and 0.25 when daily output is normalized by the monthly measurements. These results suggest that the origin of these correlations is both the linacs and the daily output check devices. Beams from different linacs, independent of their energies, have lower correlation coefficient, with a maximum of about 0.50 and a minimum of almost zero. The maximum correlation drops to almost zero if the output is normalized by the monthly measured output. Some scatter plots of pairs of beam output from the same linac show band‐like structures. These structures are blurred when the output is normalized by the monthly calibrated output. Fourier decomposition of the quasi‐periodic output is consistent with a 1/f power law. The output variation appears to come from a distorted normal distribution with a mean of slightly greater than unity. The quasi‐periodic behavior is manifested in the seasonally averaged output, showing annual variability with negative variations in the winter and positive in the summer. This trend is weakened when the daily output is normalized by the monthly calibrated output, indicating that the variation of the periodic component may be intrinsic to both the linacs and the daily measurement devices. Actual linac output was measured monthly. It needs to be adjusted once every three to six months for our tolerance and action levels. If these adjustments are artificially removed, then there is an increase in output of about 2%–4% per year. PACS numbers: 87.56bd, 87.56Fc, 87.55Qr
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Sanghangthum T, Suriyapee S, Srisatit S, Pawlicki T. Retrospective analysis of linear accelerator output constancy checks using process control techniques. J Appl Clin Med Phys 2013; 14:4032. [PMID: 23318390 PMCID: PMC5713921 DOI: 10.1120/jacmp.v14i1.4032] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2012] [Revised: 08/10/2012] [Accepted: 08/31/2012] [Indexed: 11/23/2022] Open
Abstract
Shewhart control charts have previously been suggested as a process control tool for use in routine linear accelerator (linac) output verifications. However, a comprehensive approach to process control has not been investigated for linac output verifications. The purpose of this work is to investigate a comprehensive process control approach to linac output constancy quality assurance (QA). The RBA‐3 dose constancy check was used to verify outputs of photon beams and electron beams delivered by a Varian Clinac 21EX linac. The data were collected during 2009 to 2010. Shewhart‐type control charts, exponentially weighted moving average (EWMA) charts, and capability indices were applied to these processes. The Shewhart‐type individuals chart (X‐chart) was used and the number of data points used to calculate the control limits was varied. The parameters tested for the EWMA charts (smoothing parameter (λ) and the control limit width (L)) were λ=0.05, L=2.492; λ=0.10, L=2.703; and λ=0.20, L=2.860, as well as the number of points used to estimate the initial process mean and variation. Lastly, the number of in‐control data points used to determine process capability (Cp) and acceptability (Cpk) were investigated, comparing the first in‐control run to the longest in‐control run of the process data. Cp and Cpk values greater than 1.0 were considered acceptable. The 95% confidence intervals were reported. The X‐charts detected systematic errors (e.g., device setup errors). In‐control run lengths on the X‐charts varied from 5 to 30 output measurements (about one to seven months). EWMA charts showed in‐control runs ranging from 9 to 33 output measurements (about two to eight months). The Cp and Cpk ratios are higher than 1.0 for all energies, except 12 and 20 MeV. However, 10 MV and 6, 9, and 16 MeV were in question when considering the 95% confidence limits. The X‐chart should be calculated using 8–12 data points. For EWMA chart, using 4 data points is sufficient to calculate the initial mean and variance of the process. The EWMA limits should be calculated with λ=0.10, L=2.703. At least 25–30 in‐control data points should be used to calculate the Cp and Cpk indices. PACS number: 89
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Affiliation(s)
- Taweap Sanghangthum
- Department of Nuclear Technology, Chulalongkorn University, Bangkok, Thailand
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Kapanen M, Bly R, Sipilä P, Järvinen H, Tenhunen M. How can a cost/benefit ratio be optimized for an output measurement program of external photon radiotherapy beams? Phys Med Biol 2011; 56:2119-30. [PMID: 21389356 DOI: 10.1088/0031-9155/56/7/014] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
We estimated cost/benefit ratios for different quality control programs of radiation output measurements of medical linear accelerators. The cost/benefit ratios of quality control (QC) programs (a combination of output measurement time interval and measurement action levels) were defined as workload divided by achievable dose accuracy. Dose accuracy was assumed to be inversely proportional to the 99% confidence limit of shifts of total treatment doses and workload as inversely proportional to the output measurement time interval. Our previously reported method was used to estimate the distribution of shifts of total treatment doses due to changes in accelerator radiation output (Gy/MU). The confidence limits of dose shifts were estimated for different QC programs and for different levels of output measurement reproducibility. Output shifts used in the estimations had previously been observed for four linear accelerators over 5 years. We observed that the cost/benefit ratio increases remarkably when the output measurement time interval is less than 1 month. The ratio depends strongly on the action levels and reproducibility of the QC measurements. Improvement of these factors optimizes the cost/benefit ratio by a factor of several times. The most cost-effective output measurement time interval to achieve 99% confidence limits of ±2, ±2.5 or ±3% for dose shifts ranged from 0.25 month to as much as 6 months depending on the factors given above and the intended accuracy level. It is several times more cost effective to increase dose accuracy by lowering the action levels of the QC measurements and by attempting to improve their reproducibility than by simply shortening the time interval of the output measurements. Methods improving utilization and interpretation of the results of the QC measurements play a key role in further optimization of cost/benefit ratios in dosimetric QC.
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Affiliation(s)
- Mika Kapanen
- Department of Oncology, Helsinki University Central Hospital, POB-180, 00029 HUS, Finland.
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