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Rippke C, Renkamp CK, Attieh C, Schlüter F, Buchele C, Debus J, Alber M, Klüter S. Leaf-individual calibration for a double stack multileaf collimator in photon radiotherapy. Phys Imaging Radiat Oncol 2023; 27:100477. [PMID: 37635846 PMCID: PMC10457557 DOI: 10.1016/j.phro.2023.100477] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2023] [Revised: 07/20/2023] [Accepted: 07/22/2023] [Indexed: 08/29/2023] Open
Abstract
Background and Purpose In online adaptive stereotactic body radiotherapy treatments, linear accelerator delivery accuracy is essential. Recently introduced double stack multileaf collimators (MLCs) have new facets in their calibration. We established a radiation-based leaf-individual calibration (LIMCA) method for double stack MLCs. Materials and Methods MLC leaf positions were evaluated from four cardinal angles with test patterns at measurement positions throughout the radiation field on EBT3 radiochromic film for each single stack. The accuracy of the method and repeatability of the results were assessed. The effect of MLC positioning errors was characterized for a measured output factor curve and a clinical patient plan. Results All positions in the motor step - position calibration file were optimized in the established LIMCA method. The resulting double stack mean accuracy for all angles was 0.2 ± 0.1 mm for X1 (left bank) and 0.2 ± 0.2 mm for X2 (right bank). The accuracy of the leaf position evaluation was 0.2 mm (95% confidence level). The MLC calibration remained stable over four months. Small MLC leaf position errors (e.g. 1.2 mm field size reduction) resulted in important dose errors (-5.8 %) for small quadratic fields of 0.83 × 0.83 cm2. Single stack position accuracy was essential for highly modulated treatment plans. Conclusions LIMCA is a new double stack MLC calibration method that increases treatment accuracy from four angles and for all moving leaves.
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Affiliation(s)
- Carolin Rippke
- Department of Radiation Oncology, Heidelberg University Hospital, Heidelberg, Baden-Württemberg, Germany
- Heidelberg Institute of Radiation Oncology (HIRO), National Center for Radiation Oncology (NCRO), Heidelberg, Baden-Württemberg, Germany
- Medical Faculty, University of Heidelberg, Heidelberg, Baden-Württemberg, Germany
| | - C. Katharina Renkamp
- Department of Radiation Oncology, Heidelberg University Hospital, Heidelberg, Baden-Württemberg, Germany
- Heidelberg Institute of Radiation Oncology (HIRO), National Center for Radiation Oncology (NCRO), Heidelberg, Baden-Württemberg, Germany
| | | | - Fabian Schlüter
- Department of Radiation Oncology, Heidelberg University Hospital, Heidelberg, Baden-Württemberg, Germany
- Heidelberg Institute of Radiation Oncology (HIRO), National Center for Radiation Oncology (NCRO), Heidelberg, Baden-Württemberg, Germany
| | - Carolin Buchele
- Department of Radiation Oncology, Heidelberg University Hospital, Heidelberg, Baden-Württemberg, Germany
- Heidelberg Institute of Radiation Oncology (HIRO), National Center for Radiation Oncology (NCRO), Heidelberg, Baden-Württemberg, Germany
- Medical Faculty, University of Heidelberg, Heidelberg, Baden-Württemberg, Germany
| | - Jürgen Debus
- Department of Radiation Oncology, Heidelberg University Hospital, Heidelberg, Baden-Württemberg, Germany
- Heidelberg Institute of Radiation Oncology (HIRO), National Center for Radiation Oncology (NCRO), Heidelberg, Baden-Württemberg, Germany
- Medical Faculty, University of Heidelberg, Heidelberg, Baden-Württemberg, Germany
- National Center for Tumor Diseases (NCT), Heidelberg, Baden-Württemberg, Germany
- Heidelberg Ion-Beam Therapy Center (HIT), Heidelberg, Baden-Württemberg, Germany
- German Cancer Consortium (DKTK), Core-center Heidelberg, Heidelberg, Baden-Württemberg, Germany
- Clinical Cooperation Unit Radiation Oncology, German Cancer Research Center (DKFZ), Heidelberg, Baden-Württemberg, Germany
| | - Markus Alber
- Department of Radiation Oncology, Heidelberg University Hospital, Heidelberg, Baden-Württemberg, Germany
- Heidelberg Institute of Radiation Oncology (HIRO), National Center for Radiation Oncology (NCRO), Heidelberg, Baden-Württemberg, Germany
- Medical Faculty, University of Heidelberg, Heidelberg, Baden-Württemberg, Germany
| | - Sebastian Klüter
- Department of Radiation Oncology, Heidelberg University Hospital, Heidelberg, Baden-Württemberg, Germany
- Heidelberg Institute of Radiation Oncology (HIRO), National Center for Radiation Oncology (NCRO), Heidelberg, Baden-Württemberg, Germany
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Ma Y, Mou X, Beeraka NM, Guo Y, Liu J, Dai J, Fan R. Machine Log File and Calibration Errors-based Patient-specific Quality Assurance (QA) for Volumetric Modulated Arc Therapy (VMAT). Curr Pharm Des 2023; 29:2738-2751. [PMID: 37916622 DOI: 10.2174/0113816128226519231017050459] [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: 09/14/2022] [Revised: 05/19/2023] [Accepted: 06/05/2023] [Indexed: 11/03/2023]
Abstract
INTRODUCTION Dose reconstructed based on linear accelerator (linac) log-files is one of the widely used solutions to perform patient-specific quality assurance (QA). However, it has a drawback that the accuracy of log-file is highly dependent on the linac calibration. The objective of the current study is to represent a new practical approach for a patient-specific QA during Volumetric modulated arc therapy (VMAT) using both log-file and calibration errors of linac. METHODS A total of six cases, including two head and neck neoplasms, two lung cancers, and two rectal carcinomas, were selected. The VMAT-based delivery was optimized by the TPS of Pinnacle^3 subsequently, using Elekta Synergy VMAT linac (Elekta Oncology Systems, Crawley, UK), which was equipped with 80 Multi-leaf collimators (MLCs) and the energy of the ray selected at 6 MV. Clinical mode log-file of this linac was used in this study. A series of test fields validate the accuracy of log-file. Then, six plans of test cases were delivered and log-file of each was obtained. The log-file errors were added to the corresponding plans through the house script and the first reconstructed plan was obtained. Later, a series of tests were performed to evaluate the major calibration errors of the linac (dose-rate, gantry angle, MLC leaf position) and the errors were added to the first reconstruction plan to generate the second reconstruction plan. At last, all plans were imported to Pinnacle and recalculated dose distribution on patient CT and ArcCheck phantom (SUN Nuclear). For the former, both target and OAR dose differences between them were compared. For the latter, γ was evaluated by ArcCheck, and subsequently, the surface dose differences between them were performed. RESULTS Accuracy of log-file was validated. If error recordings in the log file were only considered, there were four arcs whose proportion of control points with gantry angle errors more than ± 1°larger than 35%. Errors of leaves within ± 0.5 mm were 95% for all arcs. The distinctness of a single control point MU was bigger, but the distinctness of cumulative MU was smaller. The maximum, minimum, and mean doses for all targets were distributed between -6.79E-02-0.42%, -0.38-0.4%, 2.69E-02-8.54E-02% respectively, whereas for all OAR, the maximum and mean dose were distributed between -1.16-2.51%, -1.21-3.12% respectively. For the second reconstructed dose: the maximum, minimum, and mean dose for all targets was distributed between 0.0995~5.7145%, 0.6892~4.4727%, 0.5829~1.8931% separately. Due to OAR, maximum and mean dose distribution was observed between -3.1462~6.8920%, -6.9899~1.9316%, respectively. CONCLUSION Patient-specific QA based on the log-file could reflect the accuracy of the linac execution plan, which usually has a small influence on dose delivery. When the linac calibration errors were considered, the reconstructed dose was closer to the actual delivery and the developed method was accurate and practical.
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Affiliation(s)
- Yangguang Ma
- Department of Radiation Oncology, First Affiliated Hospital of Zhengzhou University, Zhengzhou 450052, China
- School of Information and Communications Engineering, Xi'AN Jiaotong University, Xi'an 710049, China
| | - Xuanqin Mou
- School of Information and Communications Engineering, Xi'AN Jiaotong University, Xi'an 710049, China
| | - Narasimha M Beeraka
- Raghavendra Institute of Pharmaceutical Education and Research (RIPER), Anantapuramu, Chiyyedu, Andhra Pradesh 515721, India
- Department of Human Anatomy, I.M. Sechenov First Moscow State Medical University of the Ministry of Health of the Russian Federation (Sechenov University), 8/2 Trubetskaya Str., Moscow 119991, Russia
| | - Yuexin Guo
- Department of Radiation Oncology, First Affiliated Hospital of Zhengzhou University, Zhengzhou 450052, China
| | - Junqi Liu
- Department of Radiation Oncology, First Affiliated Hospital of Zhengzhou University, Zhengzhou 450052, China
| | - Jianrong Dai
- Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer, Cancer Hospital, Chinese Academy of Medical Science and Peking Union Medical College, Beijing 100021, China
| | - Ruitai Fan
- Department of Radiation Oncology, First Affiliated Hospital of Zhengzhou University, Zhengzhou 450052, China
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Woodings SJ, de Vries JHW, Kok JMG, Hackett SL, van Asselen B, Bluemink JJ, van Zijp HM, van Soest TL, Roberts DA, Lagendijk JJW, Raaymakers BW, Wolthaus JWH. Acceptance procedure for the linear accelerator component of the 1.5 T MRI-linac. J Appl Clin Med Phys 2021; 22:45-59. [PMID: 34275176 PMCID: PMC8364272 DOI: 10.1002/acm2.13068] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2019] [Revised: 04/14/2020] [Accepted: 07/09/2020] [Indexed: 11/11/2022] Open
Abstract
Purpose To develop and implement an acceptance procedure for the new Elekta Unity 1.5 T MRI‐linac. Methods Tests were adopted and, where necessary adapted, from AAPM TG106 and TG142, IEC 60976 and NCS 9 and NCS 22 guidelines. Adaptations were necessary because of the atypical maximum field size (57.4 × 22 cm), FFF beam, the non‐rotating collimator, the absence of a light field, the presence of the 1.5 T magnetic field, restricted access to equipment within the bore, fixed vertical and lateral table position, and the need for MR image to MV treatment alignment. The performance specifications were set for stereotactic body radiotherapy (SBRT). Results The new procedure was performed similarly to that of a conventional kilovoltage x‐ray (kV) image guided radiation therapy (IGRT) linac. Results were acquired for the first Unity system. Conclusions A comprehensive set of tests was developed, described and implemented for the MRI‐linac. The MRI‐linac met safety requirements for patients and operators. The system delivered radiation very accurately with, for example a gantry rotation locus of isocenter of radius 0.38 mm and an average MLC absolute positional error of 0.29 mm, consistent with use for SBRT. Specifications for clinical introduction were met.
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Affiliation(s)
- Simon J Woodings
- Department of Radiotherapy, University Medical Center Utrecht, Utrecht, The Netherlands
| | - J H Wilfred de Vries
- Department of Radiotherapy, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Jan M G Kok
- Department of Radiotherapy, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Sara L Hackett
- Department of Radiotherapy, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Bram van Asselen
- Department of Radiotherapy, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Johanna J Bluemink
- Department of Radiotherapy, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Helena M van Zijp
- Department of Radiotherapy, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Theo L van Soest
- Department of Radiotherapy, University Medical Center Utrecht, Utrecht, The Netherlands
| | | | - Jan J W Lagendijk
- Department of Radiotherapy, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Bas W Raaymakers
- Department of Radiotherapy, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Jochem W H Wolthaus
- Department of Radiotherapy, University Medical Center Utrecht, Utrecht, The Netherlands
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Woodings SJ, Bluemink JJ, de Vries JHW, Niatsetski Y, van Veelen B, Schillings J, Kok JGM, Wolthaus JWH, Hackett SL, van Asselen B, van Zijp HM, Pencea S, Roberts DA, Lagendijk JJW, Raaymakers BW. Beam characterisation of the 1.5 T MRI-linac. Phys Med Biol 2018. [PMID: 29521280 DOI: 10.1088/1361-6560/aab566] [Citation(s) in RCA: 48] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
As a prerequisite for clinical treatments it was necessary to characterize the Elekta 1.5 T MRI-linac 7 MV FFF radiation beam. Following acceptance testing, beam characterization data were acquired with Semiflex 3D (PTW 31021), microDiamond (PTW 60019), and Farmer-type (PTW 30013 and IBA FC65-G) detectors in an Elekta 3D scanning water phantom and a PTW 1D water phantom. EBT3 Gafchromic film and ion chamber measurements in a buildup cap were also used. Special consideration was given to scan offsets, detector effective points of measurement and avoiding air gaps. Machine performance has been verified and the system satisfied the relevant beam requirements of IEC60976. Beam data were acquired for field sizes between 1 × 1 and 57 × 22 cm2. New techniques were developed to measure percentage depth dose (PDD) curves including the electron return effect at beam exit, which exhibits an electron-type practical range of 1.2 ± 0.1 cm. The Lorentz force acting on the secondary charged particles creates an asymmetry in the crossline profiles with an average shift of +0.24 cm. For a 10 × 10 cm2 beam, scatter from the cryostat contributes 1% of the dose at isocentre. This affects the relative output factors, scatter factors and beam profiles, both in-field and out-of-field. The average 20%-80% penumbral width measured for small fields with a microDiamond detector at 10 cm depth is 0.50 cm. MRI-linac penumbral widths are very similar to that of the Elekta Agility linac MLC, as is the near-surface dose PDD(0.2 cm) = 57%. The entrance surface dose is ∼36% of Dmax. Cryostat transmission is quantified for inclusion within the treatment planning system. As a result, the 1.5 T MRI-linac 7 MV FFF beam has been characterised for the first time and is suitable for clinical use. This was a key step towards the first clinical treatments with the MRI-linac, which were delivered at University Medical Center Utrecht in May 2017 (Raaymakers et al 2017 Phys. Med. Biol. 62 L41-50).
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Affiliation(s)
- S J Woodings
- Department of Radiotherapy, University Medical Center Utrecht, Heidelberglaan 100, Utrecht 3584 CX, Netherlands
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Li Y, Chen L, Zhu J, Wang B, Liu X. A quantitative method to the analysis of MLC leaf position and speed based on EPID and EBT3 film for dynamic IMRT treatment with different types of MLC. J Appl Clin Med Phys 2017; 18:106-115. [PMID: 28517613 PMCID: PMC7663986 DOI: 10.1002/acm2.12102] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2017] [Revised: 04/03/2017] [Accepted: 03/04/2017] [Indexed: 12/03/2022] Open
Abstract
A quantitative method based on the electronic portal imaging system (EPID) and film was developed for MLC position and speed testing; this method was used for three MLC types (Millennium, MLCi, and Agility MLC). To determine the leaf position, a picket fence designed by the dynamic (DMLC) model was used. The full‐width half‐maximum (FWHM) values of each gap measured by EPID and EBT3 were converted to the gap width using the FWHM versus nominal gap width relationship. The algorithm developed for the picket fence analysis was able to quantify the gap width, the distance between gaps, and each individual leaf position. To determine the leaf speed, a 0.5 × 20 cm2MLC‐defined sliding gap was applied across a 14 × 20 cm2 symmetry field. The linacs ran at a fixed‐dose rate. The use of different monitor units (MUs) for this test led to different leaf speeds. The effect of leaf transmission was considered in a speed accuracy analysis. The difference between the EPID and film results for the MLC position is less than 0.1 mm. For the three MLC types, twice the standard deviation (2 SD) is provided; 0.2, 0.4, and 0.4 mm for gap widths of three MLC types, and 0.1, 0.2, and 0.2 mm for distances between gaps. The individual leaf positions deviate from the preset positions within 0.1 mm. The variations in the speed profiles for the EPID and EBT3 results are consistent, but the EPID results are slightly better than the film results. Different speeds were measured for each MLC type. For all three MLC types, speed errors increase with increasing speed. The analysis speeds deviate from the preset speeds within approximately 0.01 cm s−1. This quantitative analysis of MLC position and speed provides an intuitive evaluation for MLC quality assurance (QA).
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Affiliation(s)
- Yinghui Li
- School of Physics, Sun Yat-sen University, Guangzhou, Guangdong, China
| | - Lixin Chen
- State Key Laboratory of Oncology in South China, Sun Yat-sen University Cancer Center, Guangzhou, Guangdong, China
| | - Jinhan Zhu
- State Key Laboratory of Oncology in South China, Sun Yat-sen University Cancer Center, Guangzhou, Guangdong, China
| | - Bin Wang
- State Key Laboratory of Oncology in South China, Sun Yat-sen University Cancer Center, Guangzhou, Guangdong, China
| | - Xiaowei Liu
- School of Physics, Sun Yat-sen University, Guangzhou, Guangdong, China
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Mans A, Schuring D, Arends MP, Vugts CAJM, Wolthaus JWH, Lotz HT, Admiraal M, Louwe RJW, Öllers MC, van de Kamer JB. The NCS code of practice for the quality assurance and control for volumetric modulated arc therapy. Phys Med Biol 2016; 61:7221-7235. [PMID: 27649474 DOI: 10.1088/0031-9155/61/19/7221] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
In 2010, the NCS (Netherlands Commission on Radiation Dosimetry) installed a subcommittee to develop guidelines for quality assurance and control for volumetric modulated arc therapy (VMAT) treatments. The report (published in 2015) has been written by Dutch medical physicists and has therefore, inevitably, a Dutch focus. This paper is a condensed version of these guidelines, the full report in English is freely available from the NCS website www.radiationdosimetry.org. After describing the transition from IMRT to VMAT, the paper addresses machine quality assurance (QA) and treatment planning system (TPS) commissioning for VMAT. The final section discusses patient specific QA issues such as the use of class solutions, measurement devices and dose evaluation methods.
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Affiliation(s)
- Anton Mans
- Department of Radiation Oncology, Netherlands Cancer Institute, Amsterdam, The Netherlands
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Katsuta Y, Kadoya N, Fujita Y, Shimizu E, Matsunaga K, Matsushita H, Majima K, Jingu K. Quantification of residual dose estimation error on log file-based patient dose calculation. Phys Med 2016; 32:701-5. [PMID: 27162084 DOI: 10.1016/j.ejmp.2016.04.015] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/06/2016] [Revised: 04/02/2016] [Accepted: 04/29/2016] [Indexed: 11/30/2022] Open
Abstract
PURPOSE The log file-based patient dose estimation includes a residual dose estimation error caused by leaf miscalibration, which cannot be reflected on the estimated dose. The purpose of this study is to determine this residual dose estimation error. METHODS AND MATERIALS Modified log files for seven head-and-neck and prostate volumetric modulated arc therapy (VMAT) plans simulating leaf miscalibration were generated by shifting both leaf banks (systematic leaf gap errors: ±2.0, ±1.0, and ±0.5mm in opposite directions and systematic leaf shifts: ±1.0mm in the same direction) using MATLAB-based (MathWorks, Natick, MA) in-house software. The generated modified and non-modified log files were imported back into the treatment planning system and recalculated. Subsequently, the generalized equivalent uniform dose (gEUD) was quantified for the definition of the planning target volume (PTV) and organs at risks. RESULTS For MLC leaves calibrated within ±0.5mm, the quantified residual dose estimation errors that obtained from the slope of the linear regression of gEUD changes between non- and modified log file doses per leaf gap are in head-and-neck plans 1.32±0.27% and 0.82±0.17Gy for PTV and spinal cord, respectively, and in prostate plans 1.22±0.36%, 0.95±0.14Gy, and 0.45±0.08Gy for PTV, rectum, and bladder, respectively. CONCLUSIONS In this work, we determine the residual dose estimation errors for VMAT delivery using the log file-based patient dose calculation according to the MLC calibration accuracy.
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Affiliation(s)
- Yoshiyuki Katsuta
- Department of Radiology, Takeda General Hospital, Aizuwakamatsu, Japan; Department of Radiation Oncology, Tohoku University Graduate School of Medicine, Sendai, Japan
| | - Noriyuki Kadoya
- Department of Radiation Oncology, Tohoku University Graduate School of Medicine, Sendai, Japan.
| | - Yukio Fujita
- Department of Radiation Oncology, Tokai University Graduate School of Medicine, Isehara, Japan
| | - Eiji Shimizu
- Department of Radiology, Takeda General Hospital, Aizuwakamatsu, Japan
| | - Kenichi Matsunaga
- Department of Radiology, Takeda General Hospital, Aizuwakamatsu, Japan
| | - Haruo Matsushita
- Department of Radiation Oncology, Tohoku University Graduate School of Medicine, Sendai, Japan
| | - Kazuhiro Majima
- Department of Radiology, Takeda General Hospital, Aizuwakamatsu, Japan
| | - Keiichi Jingu
- Department of Radiation Oncology, Tohoku University Graduate School of Medicine, Sendai, Japan
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Bedford JL, Chajecka-Szczygielska H, Thomas MDR. Quality control of VMAT synchronization using portal imaging. J Appl Clin Med Phys 2015; 16:5238. [PMID: 25679179 PMCID: PMC5689994 DOI: 10.1120/jacmp.v16i1.5238] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2014] [Revised: 10/07/2014] [Accepted: 09/29/2014] [Indexed: 02/01/2023] Open
Abstract
For accurate delivery of volumetric-modulated arc therapy (VMAT), the gantry position should be synchronized with the multileaf collimator (MLC) leaf positions and the dose rate. This study, therefore, aims to implement quality control (QC) of VMAT synchronization, with as few arcs as possible and with minimal data handling time, using portal imaging. A steel bar of diameter 12 mm is accurately positioned in the G-T direction, 80 mm laterally from the isocenter. An arc prescription irradiates the bar with a 16 mm × 220 mm field during a complete 360° arc, so as to cast a shadow of the bar onto the portal imager. This results in a sinusoidal sweep of the field and shadow across the portal imager and back. The method is evaluated by simulating gantry position errors of 1°-9° at one control point, dose errors of 2 monitor units to 20 monitor units (MU) at one control point (0.3%-3% overall), and MLC leaf position errors of 1 mm - 6 mm at one control point. Inhomogeneity metrics are defined to characterize the synchronization of all leaves and of individual leaves with respect to the complete set. Typical behavior is also investigated for three models of accelerator. In the absence of simulated errors, the integrated images show uniformity, and with simulated delivery errors, irregular patterns appear. The inhomogeneity metrics increase by 67% due to a 4° gantry position error, 33% due to an 8 MU (1.25%) dose error, and 70% due to a 2 mm MLC leaf position error. The method is more sensitive to errors at gantry angle 90°/270° than at 0°/180° due to the geometry of the test. This method provides fast and effective VMAT QC suitable for inclusion in a monthly accelerator QC program. The test is able to detect errors in the delivery of individual control points, with the possibility of using movie images to further investigate suspicious image features.
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Létourneau D, Wang A, Amin MN, Pearce J, McNiven A, Keller H, Norrlinger B, Jaffray DA. Multileaf collimator performance monitoring and improvement using semiautomated quality control testing and statistical process control. Med Phys 2014; 41:121713. [DOI: 10.1118/1.4901520] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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A quality assurance technique for the static multileaf collimator mode based on intrinsic base lines. JOURNAL OF RADIATION RESEARCH AND APPLIED SCIENCES 2014. [DOI: 10.1016/j.jrras.2014.03.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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Tatsumi D, Nakada R, Ienaga A, Yomoda A, Inoue M, Ichida T, Hosono M. [Positional accuracy and quality assurance of Backup JAWs required for volumetric modulated arc therapy]. Nihon Hoshasen Gijutsu Gakkai Zasshi 2012; 68:1486-91. [PMID: 23171770 DOI: 10.6009/jjrt.2012_jsrt_68.11.1486] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The tolerance of the Backup diaphragm (Backup JAW) setting in Elekta linac was specified as 2 mm according to the AAPM TG-142 report. However, the tolerance and the quality assurance procedure for volumetric modulated arc therapy (VMAT) was not provided. This paper describes positional accuracy and quality assurance procedure of the Backup JAWs required for VMAT. It was found that a gap-width error of the Backup JAW by a sliding window test needed to be less than 1.5 mm for prostate VMAT delivery. It was also confirmed that the gap-widths had been maintained with an error of 0.2 mm during the past one year.
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Sumida I, Yamaguchi H, Kizaki H, Koizumi M, Ogata T, Takahashi Y, Yoshioka Y. Quality assurance of MLC leaf position accuracy and relative dose effect at the MLC abutment region using an electronic portal imaging device. JOURNAL OF RADIATION RESEARCH 2012; 53:798-806. [PMID: 22843372 PMCID: PMC3430416 DOI: 10.1093/jrr/rrs038] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/21/2011] [Revised: 05/15/2012] [Accepted: 05/28/2012] [Indexed: 06/01/2023]
Abstract
We investigated an electronic portal image device (EPID)-based method to see whether it provides effective and accurate relative dose measurement at abutment leaves in terms of positional errors of the multi-leaf collimator (MLC) leaf position. A Siemens ONCOR machine was used. For the garden fence test, a rectangular field (0.2 20 cm) was sequentially irradiated 11 times at 2-cm intervals. Deviations from planned leaf positions were calculated. For the nongap test, relative doses at the MLC abutment region were evaluated by sequential irradiation of a rectangular field (2 20 cm) 10 times with a MLC separation of 2 cm without a leaf gap. The integral signal in a region of interest was set to position A (between leaves) and B (neighbor of A). A pixel value at position B was used as background and the pixel ratio (A/B 100) was calculated. Both tests were performed at four gantry angles (0, 90, 180 and 270°) four times over 1 month. For the nongap test the difference in pixel ratio between the first and last period was calculated. Regarding results, average deviations from planned positions with the garden fence test were within 0.5 mm at all gantry angles, and at gantry angles of 90 and 270° tended to decrease gradually over the month. For the nongap test, pixel ratio tended to increase gradually in all leaves, leading to a decrease in relative doses at abutment regions. This phenomenon was affected by both gravity arising from the gantry angle, and the hardware-associated contraction of field size with this type of machine.
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Affiliation(s)
- Iori Sumida
- Department of Oral and Maxillofacial Radiology, Osaka University Graduate School of Dentistry, 1-8 Yamada-oka, Suita, Osaka, 565-0871 Japan.
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Tatsumi D, Nakada R, Yomoda A, Ishii K, Tsutsumi S, Inoue M, Ichida T, Hosono MN, Miki Y. Minimum requirements for commissioning and long-term quality assurance of Elekta multi-leaf collimator for volumetric modulated arc therapy. Radiol Phys Technol 2012; 6:98-106. [PMID: 22890571 DOI: 10.1007/s12194-012-0175-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2012] [Revised: 08/01/2012] [Accepted: 08/02/2012] [Indexed: 11/25/2022]
Abstract
We have proposed minimum requirements for commissioning and long-term quality assurance (QA) of an Elekta multi-leaf collimator (MLC) for volumetric modulated arc therapy (VMAT). The MLC leaf position accuracy during VMAT delivery was evaluated with the use of three different QA test plans: (1) a leaf gap-width test between opposing leaves by measurement of the isocenter dose during constant-gap sliding-window delivery with varied dose rates, MLC leaf speeds, and gantry angles; (2) a leaf position test by picket-fence delivery with and without gantry rotation; and (3) a leaf-bank symmetry test by measurement of the field geometry with different collimator angles at a fixed gantry position. All the QA test plans were created using an ERGO++ treatment-planning system. The leaf gap-width deviation was within 0.2 mm, the leaf position deviation was within 0.5 mm, and the leaf-bank symmetry error was within 0.5 mm under all the test conditions. MLC leaf position accuracy and long-term stability were confirmed by the proposed procedures.
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Affiliation(s)
- Daisaku Tatsumi
- Department of Radiology, Osaka City University Hospital, 1-5-7 Asahimachi, Abenoku, Osaka 545-8586, Japan.
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Tatsumi D, Hosono MN, Nakada R, Ishii K, Tsutsumi S, Inoue M, Ichida T, Miki Y. Direct impact analysis of multi-leaf collimator leaf position errors on dose distributions in volumetric modulated arc therapy: a pass rate calculation between measured planar doses with and without the position errors. Phys Med Biol 2011; 56:N237-46. [DOI: 10.1088/0031-9155/56/20/n03] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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15
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Rødal J, Waldeland E, Søvik Å, Malinen E. Dosimetric verification of biologically adapted IMRT. Med Phys 2011; 38:2586-94. [DOI: 10.1118/1.3581406] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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16
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Clews L, Greer PB. An EPID based method for efficient and precise asymmetric jaw alignment quality assurance. Med Phys 2010; 36:5488-96. [PMID: 20095261 DOI: 10.1118/1.3253463] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE The aim of this work was to investigate the use of amorphous silicon electronic portal imaging devices (EPIDs) for regular quality assurance of linear accelerator asymmetric jaw junctioning. METHODS The method uses the beam central axis position on the EPID measured to subpixel accuracy found from two EPID images with 180 degrees opposing collimator angles. Individual zero jaw position ("half-beam blocked") images are then acquired and the jaw position precisely determined for each using penumbra interpolation. The accuracy of determining jaw position with the EPID method was measured by translating a block (simulating a jaw) by known distances, using a translation stage, and then measuring each translation distance with the EPID. To establish the utility of EPID based junction dose measurements, radiographic film measurements of junction dose maxima/minima as a function of jaw gap/overlap were made and compared to EPID measurements. Using the method, the long-term stability of zero jaw positioning was assessed for four linear accelerators over a 1-1.5 yr time period. The stability at nonzero gantry angles was assessed over a shorter time period. RESULTS The accuracy of determining jaw translations with the method was within 0.14 mm found using the translation stage [standard deviation (SD) of 0.037 mm]. The junction doses measured with the EPID were different from film due to the nonwater equivalent EPID scattering properties and hence different penumbra profile. The doses were approximately linear with gap or overlap, and a correction factor was derived to convert EPID measured junction dose to film measured equivalent. Over a 1 yr period, the zero jaw positions at gantry zero position were highly reproducible with an average SD of 0.07 mm for the 16 collimator jaws examined. However, the average jaw positions ranged from -0.7 to 0.9 mm relative to central axis for the different jaws. The zero jaw position was also reproducible at gantry 90 degrees position with 0.1 mm SD variation with the mean jaw position offset from the gantry zero position consistently by 0.3-0.4 mm for the jaws studied. CONCLUSIONS The EPID based method is efficient and yields more precise data on linear accelerator jaw positioning and reproducibility than previous methods. The results highlight that zero jaw positions are highly reproducible to a level much smaller than the displayed jaw resolution and that there is a need for better methods to calibrate the jaw positioning.
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Affiliation(s)
- Luke Clews
- Calvary Mater Newcastle Hospital, Newcastle, New South Wales, 2298, Australia
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Klein EE, Hanley J, Bayouth J, Yin FF, Simon W, Dresser S, Serago C, Aguirre F, Ma L, Arjomandy B, Liu C, Sandin C, Holmes T. Task Group 142 report: quality assurance of medical accelerators. Med Phys 2009; 36:4197-212. [PMID: 19810494 DOI: 10.1118/1.3190392] [Citation(s) in RCA: 966] [Impact Index Per Article: 64.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The task group (TG) for quality assurance of medical accelerators was constituted by the American Association of Physicists in Medicine's Science Council under the direction of the Radiation Therapy Committee and the Quality Assurance and Outcome Improvement Subcommittee. The task group (TG-142) had two main charges. First to update, as needed, recommendations of Table II of the AAPM TG-40 report on quality assurance and second, to add recommendations for asymmetric jaws, multileaf collimation (MLC), and dynamic/virtual wedges. The TG accomplished the update to TG-40, specifying new test and tolerances, and has added recommendations for not only the new ancillary delivery technologies but also for imaging devices that are part of the linear accelerator. The imaging devices include x-ray imaging, photon portal imaging, and cone-beam CT. The TG report was designed to account for the types of treatments delivered with the particular machine. For example, machines that are used for radiosurgery treatments or intensity-modulated radiotherapy (IMRT) require different tests and/or tolerances. There are specific recommendations for MLC quality assurance for machines performing IMRT. The report also gives recommendations as to action levels for the physicists to implement particular actions, whether they are inspection, scheduled action, or immediate and corrective action. The report is geared to be flexible for the physicist to customize the QA program depending on clinical utility. There are specific tables according to daily, monthly, and annual reviews, along with unique tables for wedge systems, MLC, and imaging checks. The report also gives specific recommendations regarding setup of a QA program by the physicist in regards to building a QA team, establishing procedures, training of personnel, documentation, and end-to-end system checks. The tabulated items of this report have been considerably expanded as compared with the original TG-40 report and the recommended tolerances accommodate differences in the intended use of the machine functionality (non-IMRT, IMRT, and stereotactic delivery).
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Affiliation(s)
- Eric E Klein
- Washington University, St. Louis, Missouri, USA.
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18
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Yan G, Liu C, Simon TA, Peng LC, Fox C, Li JG. On the sensitivity of patient-specific IMRT QA to MLC positioning errors. J Appl Clin Med Phys 2009; 10:120-128. [PMID: 19223841 PMCID: PMC5720508 DOI: 10.1120/jacmp.v10i1.2915] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2008] [Revised: 08/26/2008] [Accepted: 09/07/2008] [Indexed: 12/22/2022] Open
Abstract
Accurate multileaf collimator (MLC) leaf positioning plays an essential role in the effective implementation of intensity modulated radiation therapy (IMRT). This work evaluates the sensitivity of current patient-specific IMRT quality assurance (QA) procedures to minor MLC leaf positioning errors. Random errors of up to 2 mm and systematic errors of +/-1 mm and +/-2 mm in MLC leaf positions were introduced into 8 clinical IMRT patient plans (totaling 53 fields). Planar dose distributions calculated with modified plans were compared to dose distributions measured with both radiochromic films and a diode matrix. The agreement between calculation and measurement was evaluated using both absolute distance-to-agreement (DTA) analysis and gamma index with 2%/2 mm and 3%/3 mm criteria. It was found that both the radiochromic film and the diode matrix could only detect systematic errors on the order of 2 mm or above. The diode array had larger sensitivity than film due to its excellent detector response (such as small variation, linear response, etc.). No difference was found between DTA analysis and gamma index in terms of the sensitivity to MLC positioning errors. Higher sensitivity was observed with 2%/2 mm than with 3%/3 mm in general. When using the diode array and 2%/2 mm criterion, the IMRT QA procedure showed strongest sensitivity to MLC position errors and, at the same time, achieved clinically acceptable passing rates. More accurate dose calculation and measurement would further enhance the sensitivity of patient-specific IMRT QA to MLC positioning errors. However, considering the significant dosimetric effect such MLC errors could cause, patient-specific IMRT QA should be combined with a periodic MLC QA program in order to guarantee the accuracy of IMRT delivery.
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Affiliation(s)
- Guanghua Yan
- Department of Radiation Oncology, University of Florida, Gainesville, FL, U.S.A.,Department of Nuclear and Radiological Engineering, University of Florida, Gainesville, FL, U.S.A
| | - Chihray Liu
- Department of Radiation Oncology, University of Florida, Gainesville, FL, U.S.A
| | - Thomas A Simon
- Department of Radiation Oncology, University of Florida, Gainesville, FL, U.S.A.,Department of Nuclear and Radiological Engineering, University of Florida, Gainesville, FL, U.S.A
| | - Lee-Cheng Peng
- Department of Radiation Oncology, University of Florida, Gainesville, FL, U.S.A.,Department of Nuclear and Radiological Engineering, University of Florida, Gainesville, FL, U.S.A
| | - Christopher Fox
- Department of Radiation Oncology, University of Florida, Gainesville, FL, U.S.A
| | - Jonathan G Li
- Department of Radiation Oncology, University of Florida, Gainesville, FL, U.S.A
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Sastre-Padro M, Lervåg C, Eilertsen K, Malinen E. The performance of multileaf collimators evaluated by the stripe test. Med Dosim 2008; 34:202-6. [PMID: 19647629 DOI: 10.1016/j.meddos.2008.08.005] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2008] [Revised: 08/14/2008] [Accepted: 08/21/2008] [Indexed: 11/28/2022]
Abstract
The performance of 3 multileaf collimator (MLC) systems (Varian Medical Systems, Elekta, and Siemens Medical Solutions) mounted on 7 different radiotherapy linear accelerators was investigated by a stripe test. The stripe test consisted of 8 adjacent multileaf segments of 2.5 x 40 cm(2), enclosed by all leaf pairs. With 6-MV photons, the segments were used to irradiate Agfa CR films. The optical density profile of the irradiated film in the travel direction of the MLC was used to estimate the short- and long-term leaf positioning reproducibility. The short-term reproducibility was found by analyzing 6 consecutive stripe tests. The long-term reproducibility was obtained by performing 3 to 5 stripe tests over 2 months. The short-term reproducibility was mainly within 0.3 mm for all systems. For the long-term reproducibility, the Varian and Elekta MLCs were within 0.4 to 0.5 mm, while the Siemens MLC showed a wider distribution, with values up to 1 mm for some leaf pairs. The inferior long-term reproducibility of the Siemens MLCs was mainly due to a decrease of the segment size with time. In conclusion, the stripe test is a useful method for evaluating MLC performance. Furthermore, the long-term reproducibility varied among the MLC systems investigated.
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Affiliation(s)
- Maria Sastre-Padro
- Department of Medical Physics, Division of Cancer Medicine and Radiotherapy, Rikshospitalet University Hospital, Oslo, Norway.
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20
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Budgell GJ, Clarke MF. Analysis of the measurement precision of an amorphous silicon EPID used for MLC leaf position quality control and the long-term calibration stability of an optically controlled MLC. Phys Med Biol 2008; 53:N297-306. [DOI: 10.1088/0031-9155/53/15/n01] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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21
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Liu C, Simon TA, Fox C, Li J, Palta JR. Multileaf collimator characteristics and reliability requirements for IMRT Elekta system. Int J Radiat Oncol Biol Phys 2008; 71:S89-92. [PMID: 18406946 DOI: 10.1016/j.ijrobp.2007.07.2392] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2007] [Revised: 07/17/2007] [Accepted: 07/27/2007] [Indexed: 11/19/2022]
Abstract
Understanding the characteristics of a multileaf collimator (MLC) system, modeling MLC in a treatment planning system, and maintaining the mechanical accuracy of the linear accelerator gantry head system are important factors in the safe implementation of an intensity-modulated radiotherapy program. We review the characteristics of an Elekta MLC system, discuss the necessary MLC modeling parameters for a treatment planning system, and provide a novel method to establish an MLC leaf position quality assurance program. To perform quality assurance on 40 pairs of individual MLC leaves is a time-consuming and difficult task. In this report, an effective routine MLC quality assurance method based on the field edge of a backup jaw as referenced in conjunction with a diode array as a radiation detector system is discussed. The sensitivity of this test for determining the relative leaf positions was observed to be better than 0.1 mm. The Elekta MLC leaf position accuracy measured with this system has been better than 0.3 mm.
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Affiliation(s)
- Chihray Liu
- Department of Radiation Oncology, University of Florida College of Medicine, Gainesville, FL 32610-0385, USA.
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22
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Mamalui-Hunter M, Li H, Low DA. MLC quality assurance using EPID: A fitting technique with subpixel precision. Med Phys 2008; 35:2347-55. [DOI: 10.1118/1.2919560] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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23
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IMRT Delivery Performance With a Varian Multileaf Collimator. Int J Radiat Oncol Biol Phys 2008; 71:S85-8. [DOI: 10.1016/j.ijrobp.2007.06.082] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2007] [Revised: 06/29/2007] [Accepted: 06/30/2007] [Indexed: 11/23/2022]
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24
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Sastre-Padro M, Welleweerd J, Malinen E, Eilertsen K, Olsen DR, van der Heide UA. Consequences of leaf calibration errors on IMRT delivery. Phys Med Biol 2007; 52:1147-56. [PMID: 17264376 DOI: 10.1088/0031-9155/52/4/019] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
IMRT treatments using multi-leaf collimators may involve a large number of segments in order to spare the organs at risk. When a large proportion of these segments are small, leaf positioning errors may become relevant and have therapeutic consequences. The performance of four head and neck IMRT treatments under eight different cases of leaf positioning errors has been studied. Systematic leaf pair offset errors in the range of +/-2.0 mm were introduced, thus modifying the segment sizes of the original IMRT plans. Thirty-six films were irradiated with the original and modified segments. The dose difference and the gamma index (with 2%/2 mm criteria) were used for evaluating the discrepancies between the irradiated films. The median dose differences were linearly related to the simulated leaf pair errors. In the worst case, a 2.0 mm error generated a median dose difference of 1.5%. Following the gamma analysis, two out of the 32 modified plans were not acceptable. In conclusion, small systematic leaf bank positioning errors have a measurable impact on the delivered dose and may have consequences for the therapeutic outcome of IMRT.
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Affiliation(s)
- M Sastre-Padro
- Department of Medical Physics, The Norwegian Radium Hospital, Montebello, N-0310 Oslo, Norway, and Department of Radiotherapy, University Medical Center Utrecht, The Netherlands.
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25
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Mohammadi M, Bezak E. Evaluation of MLC leaf positioning using a scanning liquid ionization chamber EPID. Phys Med Biol 2006; 52:N21-33. [PMID: 17183123 DOI: 10.1088/0031-9155/52/1/n03] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
A method was developed to determine the accuracy of multileaf collimator (MLC) positioning using transmitted dose maps measured by a scanning liquid ionization chamber electronic portal imaging device (SLIC-EPID). Several MLC fields were designed, using the Varian C-series standard MLC-80, as reference fields for open fields. The MLC leaves were then shifted from the reference positions along the direction of MLC leaf movement towards the central axis from 0.1 to 1.6 mm. The electronic portal images (EPIs), acquired for each case, were converted to two-dimensional dose maps using an appropriate calibration method and the relative dose difference maps were then calculated. The experiment was then performed at non-zero gantry angles in the presence of an anthropomorphic phantom for typical prostate and head and neck fields. Several standard edge detection algorithms were also used in order to find the shifted MLC leaf position. In addition, the short-term reproducibility of MLC leaf positioning was evaluated using the above-mentioned methods. It was found that the relationship between the relative dose difference and MLC leaf spatial displacement is linear. A variation of 0.2 mm in leaf position leads to approximately 4% change in the relative dose values for open fields. The variation of the relative dose difference for phantom studies depends on the phantom positioning and the EPI normalization. From the standard edge detection algorithms, used in the current study, the 'Canny' algorithm was found to be the optimum method to identify the minimum detectable MLC leaf displacements with a precision of approximately 0.1 mm for all cases. However, the result of edge detection algorithms generally is binary and there is no additional information compared to the relative dose maps. The reproducibility of MLC positions was found to be within 0.3 mm. In conclusion, a SLIC-EPID can be used for regular quality assurance (QA) of MLC leaf positioning. Despite significant difference in the pixel size of the acquired SLIC-EPIs, it can be concluded that the SLIC-EPID can be used for MLC quality assurance protocols with similar accuracy compared to amorphous silicon (a-Si) EPID results.
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Affiliation(s)
- Mohammad Mohammadi
- Department of Medical Physics, Royal Adelaide Hospital, Adelaide, SA 5000, Australia.
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26
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Pasquino M, Borca VC, Catuzzo P, Ozzello F, Tofani S. Transmission, Penumbra and Leaf Positional Accuracy in Commissioning and Quality Assurance Program of a Multileaf Collimator for Step-and-Shoot IMRT Treatments. TUMORI JOURNAL 2006; 92:511-6. [PMID: 17260492 DOI: 10.1177/030089160609200608] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Aims and background The performance characteristics of a commercial multileaf collimator (MLC) for intensity modulated radiation therapy (IMRT) and a comprehensive quality assurance program (QA) to be performed during the commissioning of the MLC were investigated. Materials and methods The midleaf transmission and interleaf leakage, the in-plane penumbra and its in-plane/cross-plane variation, the cross-plane penumbra and its in-plane/cross-plane variation, and the leaf positional accuracy of a high-energy photon (6 MV) Sli Precise Elekta linear accelerator were measured. Kodak EDR2 Ready Pack film was used for MLC transmission measurement; for the other characterization measurements we used Kodak X-Omat XV2 Ready Pack film placed at 5 cm depth in a solid RW3 phantom. Each film was digitized with a laser scanning photodensitometer VXR-12 Plus using the Omni Pro-Accept 6.0A film dosimetry system and converted to dose by means of H&D curves. The dose calibration measurements were performed with a Farmer ionization chamber according to the guidelines of the IAEA Technical Report No. 277. Results The average midleaf transmission and interleaf leakage were 1.8% ± 0.1% and 2.1% ± 0.2%, respectively. The average value of the cross-plane penumbra was 5.4 mm ± 0.3 mm with maximum variation less than 0.4 mm and 1.0 mm in the in-plane and cross-plane direction, respectively. The average value of the in-plane penumbra was 3.2 mm ± 0.2 mm and 3.5 mm ± 0.2 mm for the step side and groove side of the leaves, respectively. A dose profile perpendicular to the direction of the leaf travel passing through the central axis shows a tongue-and-groove effect of about 33%. The positional accuracy of the leaves was investigated according to AAPM Report No. 72 TG50; the deviation of the net optical density along all the match lines was less than ± 20%. Moreover, the results obtained with a step field technique showed a positional accuracy of less than 1 mm. Conclusions The results suggest the necessity of extensive knowledge of the MLC dosimetric characteristics for IMRT applications in order to allow physicists to study their influence on treatment delivery and to perform a comprehensive routine QA program of the investigated parameters.
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Affiliation(s)
- Massimo Pasquino
- SC Fisica Sanitaria,, Azienda Ospedaliera ASL 9, Ivrea, Turin, Italy.
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Vieira SC, Bolt RA, Dirkx MLP, Visser AG, Heijmen BJM. Fast, daily linac verification for segmented IMRT using electronic portal imaging. Radiother Oncol 2006; 80:86-92. [PMID: 16854483 DOI: 10.1016/j.radonc.2006.06.010] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2005] [Revised: 05/15/2006] [Accepted: 06/27/2006] [Indexed: 11/24/2022]
Abstract
PURPOSE Intensity modulated radiotherapy (IMRT) requires dedicated quality assurance (QA). Recently, we have published a method for fast (1-2 min) and accurate linac quality control for dynamic multileaf collimation, using a portal imaging device. This method is in routine use for daily leaf motion verification. The purpose of the present study was to develop an equivalent procedure for QA of IMRT with segmented (static) multileaf collimation (SMLC). MATERIALS AND METHODS The QA procedure is based on measurements performed during 3- to 8-month periods at Elekta, Siemens and Varian accelerators. On each measurement day, images were acquired for a field consisting of five 3 x 22 cm(2) segments. These 10 monitor unit (MU) segments were delivered in SMLC mode, moving the leaves from left to right. Deviations of realized leaf gap widths from the prescribed width were analysed to study the leaf positioning accuracy. To assess hysteresis in leaf positioning, the sequential delivery of the SMLC segments was also inverted. A static 20 x 20 cm(2) field was delivered with exposures between 1 and 50 MU to study the beam output and beam profile at low exposures. Comparisons with an ionisation chamber were made to verify the EPID dose measurements at low MU. Dedicated software was developed to improve the signal-to-noise ratio and to correct for image distortion. RESULTS AND CONCLUSIONS The observed long-term leaf gap reproducibility (1 standard deviation) was 0.1 mm for the Varian, and 0.2 mm for the Siemens and the Elekta accelerators. In all cases the hysteresis was negligible. Down to the lowest MU, beam output measurements performed with the EPID agreed within 1+/-1% (1SD) with ionisation chamber measurements. These findings led to a fast (3-4 min) procedure for accurate, daily linac quality control for SMLC.
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Affiliation(s)
- Sandra C Vieira
- Department of Radiation Oncology, Erasmus MC/Daniel den Hoed Cancer Center, Rotterdam, The Netherlands.
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28
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Petoukhova AL, Terhaard CHJ, Welleweerd H. Does 4MV perform better compared to 6MV in the presence of air cavities in the head and neck region? Radiother Oncol 2006; 79:203-7. [PMID: 16698100 DOI: 10.1016/j.radonc.2006.04.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2005] [Revised: 03/23/2006] [Accepted: 04/19/2006] [Indexed: 10/24/2022]
Abstract
BACKGROUND AND PURPOSE The underdose near air cavities in the head and neck region at photon energies of 4 MV and 6 MV was studied in search for clinical advantages of the 4 MV over 6 MV treatments. MATERIALS AND METHODS The on-axis and off-axis dose distributions were measured with a parallel-plate ionization chamber and films in polystyrene phantoms containing an air cavity of appropriate size based on the results of computed tomography scans. RESULTS Although most results are similar for both energies, the 4 MV photon beams give a somewhat smaller underdose effect and a faster re-build up than the 6 MV. For both energies a significant underdose effect was observed at the edge of the field in the larynx phantom. This proved to be true for small and large fields, for smaller and larger cavities, for one-beam as well as parallel-opposed beams. CONCLUSION For most clinically relevant situations there is no remarkable benefit in the use of either of the two energies.
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Affiliation(s)
- Anna L Petoukhova
- Department of Radiation Oncology, University Medical Center Utrecht, Utrecht, The Netherlands
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29
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Baker SJK, Budgell GJ, MacKay RI. Use of an amorphous silicon electronic portal imaging device for multileaf collimator quality control and calibration. Phys Med Biol 2005; 50:1377-92. [PMID: 15798330 DOI: 10.1088/0031-9155/50/7/003] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Multileaf collimator (MLC) calibration and quality control is a time-consuming procedure typically involving the processing, scanning and analysis of films to measure leaf and collimator positions. Faster and more reliable calibration procedures are required for these tasks, especially with the introduction of intensity modulated radiotherapy which requires more frequent checking and finer positional leaf tolerances than previously. A routine quality control (QC) technique to measure MLC leaf bank gain and offset, as well as minor offsets (individual leaf position relative to a reference leaf), using an amorphous silicon electronic portal imaging device (EPID) has been developed. The technique also tests the calibration of the primary and back-up collimators. A detailed comparison between film and EPID measurements has been performed for six linear accelerators (linacs) equipped with MLC and amorphous silicon EPIDs. Measurements of field size from 4 to 24 cm with the EPID were systematically smaller than film measurements over all field sizes by 0.4 mm for leaves/back-up collimators and by 0.2 mm for conventional collimators. This effect is due to the gain calibration correction applied by the EPID, resulting in a 'flattening' of primary beam profiles. Linac dependent systematic differences of up to 0.5 mm in individual leaf/collimator positions were also found between EPID and film measurements due to the difference between the mechanical and radiation axes of rotation. When corrections for these systematic differences were applied, the residual random differences between EPID and film were 0.23 mm and 0.26 mm (1 standard deviation) for field size and individual leaf/back-up collimator position, respectively. Measured gains (over a distance of 220 mm) always agreed within 0.4 mm with a standard deviation of 0.17 mm. Minor offset measurements gave a mean agreement between EPID and film of 0.01+/-0.10 mm (1 standard deviation) after correction for the tilt of the EPID and small rotational misalignments between leaf banks and the back-up collimators used as a reference straight edge. Reproducibility of EPID measurements was found to be very high, with a standard deviation of <0.05 mm for field size and <0.1 mm for individual leaf/collimator positions for a 10x10 cm2 field. A standard set of QC images (three field sizes defined both by leaves only and collimators only) can be acquired in less than 20 min and analysed in 5 min.
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Affiliation(s)
- S J K Baker
- North Western Medical Physics, Christie Hospital NHS Trust, Manchester M20 4BX, UK.
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