Quality assurance of dynamic parameters in volumetric modulated arc therapy.

OBJECTIVES The purpose of this study was to demonstrate quality assurance checks for accuracy of gantry speed and position, dose rate and multileaf collimator (MLC) speed and position for a volumetric modulated arc treatment (VMAT) modality (Synergy S; Elekta, Stockholm, Sweden), and to check that all the necessary variables and parameters were synchronous. METHODS Three tests (for gantry position-dose delivery synchronisation, gantry speed-dose delivery synchronisation and MLC leaf speed and positions) were performed. RESULTS The average error in gantry position was 0.5° and the average difference was 3 MU for a linear and a parabolic relationship between gantry position and delivered dose. In the third part of this test (sawtooth variation), the maximum difference was 9.3 MU, with a gantry position difference of 1.2°. In the sweeping field method test, a linear relationship was observed between recorded doses and distance from the central axis, as expected. In the open field method, errors were encountered at the beginning and at the end of the delivery arc, termed the "beginning" and "end" errors. For MLC position verification, the maximum error was -2.46 mm and the mean error was 0.0153 ±0.4668 mm, and 3.4% of leaves analysed showed errors of >±1 mm. CONCLUSION This experiment demonstrates that the variables and parameters of the Synergy S are synchronous and that the system is suitable for delivering VMAT using a dynamic MLC.

[1]  Karl Otto,et al.  Volumetric modulated arc therapy: IMRT in a single gantry arc. , 2007, Medical physics.

[2]  Toshikazu Imae,et al.  Quality assurance of volumetric modulated arc therapy using Elekta Synergy , 2009, Acta oncologica.

[3]  R I MacKay,et al.  Use of an amorphous silicon electronic portal imaging device for multileaf collimator quality control and calibration , 2005, Physics in medicine and biology.

[4]  Joao Seco,et al.  Evaluation of two methods of predicting MLC leaf positions using EPID measurements. , 2006, Medical physics.

[5]  C. Ling,et al.  Commissioning and quality assurance of RapidArc radiotherapy delivery system. , 2008, International journal of radiation oncology, biology, physics.

[6]  James F Dempsey,et al.  Validation of dynamic MLC-controller log files using a two-dimensional diode array. , 2003, Medical physics.

[7]  E. Schreibmann,et al.  Patient-specific quality assurance method for VMAT treatment delivery. , 2009, Medical physics.

[8]  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. , 2008, Physics in medicine and biology.

[9]  J. Dempsey,et al.  An extensive log-file analysis of step-and-shoot intensity modulated radiation therapy segment delivery errors. , 2004, Medical physics.

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

[12]  Lei Xing,et al.  Quantitative measurement of MLC leaf displacements using an electronic portal image device. , 2004, Physics in medicine and biology.

[13]  C Cameron,et al.  Sweeping-window arc therapy: an implementation of rotational IMRT with automatic beam-weight calculation , 2005, Physics in medicine and biology.

[14]  J. Bedford,et al.  Commissioning of volumetric modulated arc therapy (VMAT). , 2009, International journal of radiation oncology, biology, physics.

[15]  L. Xing,et al.  Aperture modulated arc therapy. , 2003, Physics in medicine and biology.

[16]  Cedric X. Yu,et al.  Arc-modulated radiation therapy (AMRT): a single-arc form of intensity-modulated arc therapy , 2008, Physics in medicine and biology.

[17]  Daniel A Low,et al.  MLC quality assurance using EPID: a fitting technique with subpixel precision. , 2008, Medical physics.

[18]  Cedric X. Yu,et al.  Guidance document on delivery, treatment planning, and clinical implementation of IMRT: report of the IMRT Subcommittee of the AAPM Radiation Therapy Committee. , 2003, Medical physics.

[19]  C. Ramsey,et al.  Leaf position error during conformal dynamic arc and intensity modulated arc treatments. , 2001, Medical physics.

[20]  Uwe Oelfke,et al.  Development of an optimization concept for arc-modulated cone beam therapy. , 2007, Physics in medicine and biology.