Investigation of the mechanical performance of Siemens linacs components during arc: gantry, MLC, and electronic portal imaging device

Background In radiotherapy treatments, it is crucial to monitor the performance of linac components including gantry, collimation system, and electronic portal imaging device (EPID) during arc deliveries. In this study, a simple EPID-based measurement method is suggested in conjunction with an algorithm to investigate the stability of these systems at various gantry angles with the aim of evaluating machine-related errors in treatments. Methods The EPID sag, gantry sag, changes in source-to-detector distance (SDD), EPID and collimator skewness, EPID tilt, and the sag in leaf bank assembly due to linac rotation were separately investigated by acquisition of 37 EPID images of a simple phantom with five ball bearings at various gantry angles. A fast and robust software package was developed for automated analysis of image data. Three Siemens linacs were investigated. Results The average EPID sag was within 1 mm for all tested linacs. Two machines showed >1 mm gantry sag. Changes in the SDD values were within 7.5 mm. EPID skewness and tilt values were <1° in all machines. The maximum sag in leaf bank assembly was <1 mm. Conclusion The method and software developed in this study provide a simple tool for effective investigation of the behavior of Siemens linac components with gantry rotation. Such a comprehensive study has been performed for the first time on Siemens machines.

[1]  Jan-Jakob Sonke,et al.  3D Dosimetric verification of volumetric-modulated arc therapy by portal dosimetry. , 2010, Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology.

[2]  Fugen Zhou,et al.  A novel technique for VMAT QA with EPID in cine mode on a Varian TrueBeam linac. , 2013, Physics in medicine and biology.

[3]  Martin A Ebert,et al.  An EPID-based method for comprehensive verification of gantry, EPID and the MLC carriage positional accuracy in Varian linacs during arc treatments , 2014, Radiation oncology.

[4]  Pejman Rowshanfarzad,et al.  Gantry-angle resolved VMAT pretreatment verification using EPID image prediction. , 2013, Medical physics.

[5]  Pejman Rowshanfarzad,et al.  Detection and correction for EPID and gantry sag during arc delivery using cine EPID imaging. , 2012, Medical physics.

[6]  Song Gao,et al.  Measuring the wobble of radiation field centers during gantry rotation and collimator movement on a linear accelerator. , 2011, Medical physics.

[7]  H. L. Riis,et al.  Gantry and isocenter displacements of a linear accelerator caused by an add-on micromultileaf collimator. , 2013, Medical physics.

[8]  P B Greer,et al.  Dosimetric properties of an amorphous-silicon EPID used in continuous acquisition mode for application to dynamic and arc IMRT. , 2009, Medical physics.

[9]  K M Alexander,et al.  Stereotactic body radiation therapy delivery validation , 2013 .

[10]  G J Budgell,et al.  Use of an amorphous silicon EPID for measuring MLC calibration at varying gantry angle. , 2008, Physics in medicine and biology.

[11]  Brian Winey,et al.  A fast double template convolution isocenter evaluation algorithm with subpixel accuracy. , 2011, Medical physics.

[12]  A Agnew,et al.  Monitoring daily MLC positional errors using trajectory log files and EPID measurements for IMRT and VMAT deliveries , 2014, Physics in medicine and biology.

[13]  Fang-Fang Yin,et al.  Task Group 142 report: quality assurance of medical accelerators. , 2009, Medical physics.

[14]  Harish K. Malhotra,et al.  EPID dosimetry for pretreatment quality assurance with two commercial systems , 2012, Journal of applied clinical medical physics.

[15]  Xiao-wu Deng,et al.  Gantry angle-dependent correction of dose detection error due to panel position displacement in IMRT dose verification using EPIDs. , 2014, Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics.

[16]  C D Mubata,et al.  A quality assurance procedure for the Varian multi-leaf collimator. , 1997, Physics in medicine and biology.

[17]  James A. Purdy,et al.  Utilization of Image-Guided Radiation Therapy Equipment to Enhance Stereotactic Body Radiation Therapy Commissioning , 2010 .

[18]  Peter Balter,et al.  Evaluation of IsoCal geometric calibration system for Varian linacs equipped with on‐board imager and electronic portal imaging device imaging systems , 2014, Journal of applied clinical medical physics.

[19]  Pejman Rowshanfarzad,et al.  Investigation of the sag in linac secondary collimator and MLC carriage during arc deliveries. , 2012, Physics in medicine and biology.

[20]  W Ansbacher,et al.  Three-dimensional portal image-based dose reconstruction in a virtual phantom for rapid evaluation of IMRT plans. , 2006, Medical physics.

[21]  Zdenka Kuncic,et al.  Kilovoltage intrafraction monitoring for prostate intensity modulated arc therapy: first clinical results. , 2012, International journal of radiation oncology, biology, physics.

[22]  Piotr Zygmanski,et al.  An MLC-based linac QA procedure for the characterization of radiation isocenter and room lasers' position. , 2006, Medical physics.

[23]  C C Ling,et al.  Developments in megavoltage cone beam CT with an amorphous silicon EPID: reduction of exposure and synchronization with respiratory gating. , 2005, Medical physics.

[24]  Cedric Yu,et al.  Verification of MLC based real-time tumor tracking using an electronic portal imaging device. , 2010, Medical physics.

[25]  Pejman Rowshanfarzad,et al.  Verification of the linac isocenter for stereotactic radiosurgery using cine-EPID imaging and arc delivery. , 2011, Medical physics.

[26]  Zdenka Kuncic,et al.  A system for EPID-based real-time treatment delivery verification during dynamic IMRT treatment. , 2013, Medical physics.

[27]  R. Ganapathi Raman,et al.  Pretreatment Patient Specific Quality Assurance and Gamma Index Variation Study in Gantry Dependent EPID Positions for IMRT Prostate Treatments , 2014 .

[28]  Peter B. Greer,et al.  Isocenter verification for linac‐based stereotactic radiation therapy: review of principles and techniques , 2011, Journal of applied clinical medical physics.

[29]  Helmar Bergmann,et al.  Introducing a system for automated control of rotation axes, collimator and laser adjustment for a medical linear accelerator. , 2003, Physics in medicine and biology.

[30]  H. L. Riis,et al.  A comprehensive study of the mechanical performance of gantry, EPID and the MLC assembly in Elekta linacs during gantry rotation. , 2015, The British journal of radiology.

[31]  Alejandra Rangel,et al.  Tolerances on MLC leaf position accuracy for IMRT delivery with a dynamic MLC. , 2009, Medical physics.

[32]  W. Du,et al.  Quantifying the gantry sag on linear accelerators and introducing an MLC-based compensation strategy. , 2012, Medical physics.

[33]  Cedric Yu,et al.  Verification of MLC based real-time tumor tracking using an electronic portal imaging device. , 2010, Medical physics.

[34]  Daniel A Low,et al.  Linac mechanic QA using a cylindrical phantom , 2008, Physics in medicine and biology.

[35]  Pejman Rowshanfarzad,et al.  An independent system for real-time dynamic multileaf collimation trajectory verification using EPID. , 2014, Physics in medicine and biology.

[36]  P W Chin,et al.  Correction for dose-response variations in a scanning liquid ion chamber EPID as a function of linac gantry angle. , 2004, Physics in medicine and biology.

[37]  W Mao,et al.  Real-time 3D internal marker tracking during arc radiotherapy by the use of combined MV–kV imaging , 2008, Physics in medicine and biology.

[38]  Conor K McGarry,et al.  Mechanical characterization of the varian Exact-arm and R-arm support systems for eight aS500 electronic portal imaging devices. , 2010, Medical physics.