An EPID-based method for comprehensive verification of gantry, EPID and the MLC carriage positional accuracy in Varian linacs during arc treatments

Radiation Oncology

Martin A Ebert¹  Mahsheed Sabet¹  Michael P Barnes³  Conor K McGarry²  Pejman Rowshanfarzad⁴ 

[1] Department of Radiation Oncology, Sir Charles Gairdner Hospital, Nedlands 6009, WA, Australia;Centre for Cancer Research and Cell Biology, Queen’s University Belfast, Belfast, UK;Department of Radiation Oncology, Calvary Mater Newcastle Hospital, Newcastle 2310, NSW, Australia;School of Physics, University of Western Australia, Crawley 6009, WA, Australia

关键词: Arc;    Quality assurance;    Collimator;    MLC;    EPID;    Gantry;    Sag;    Varian;    Linac;   

Others  :  1150864
DOI  :  10.1186/s13014-014-0249-8

 received in 2014-09-02, accepted in 2014-11-04,  发布年份 2014

【 摘 要 】

Background

In modern radiotherapy, it is crucial to monitor the performance of all linac components including gantry, collimation system and electronic portal imaging device (EPID) during arc deliveries. In this study, a simple EPID-based measurement method has been introduced in conjunction with an algorithm to investigate the stability of these systems during arc treatments with the aim of ensuring the accuracy of linac mechanical performance.

Methods

The Varian EPID sag, gantry sag, changes in source-to-detector distance (SDD), EPID and collimator skewness, EPID tilt, and the sag in MLC carriages as a result of linac rotation were separately investigated by acquisition of EPID images of a simple phantom comprised of 5 ball-bearings during arc delivery. A fast and robust software package was developed for automated analysis of image data. Twelve Varian linacs of different models were investigated.

Results

The average EPID sag was within 1 mm for all tested linacs. All machines showed less than 1 mm gantry sag. Changes in SDD values were within 1.7 mm except for three linacs of one centre which were within 9 mm. Values of EPID skewness and tilt were negligible in all tested linacs. The maximum sag in MLC leaf bank assemblies was around 1 mm. The EPID sag showed a considerable improvement in TrueBeam linacs.

Conclusion

The methodology and software developed in this study provide a simple tool for effective investigation of the behaviour of linac components with gantry rotation. It is reproducible and accurate and can be easily performed as a routine test in clinics.

【 授权许可】

   
2014 Rowshanfarzad et al.; licensee BioMed Central Ltd.

【 图 表 】

Figure 1.

Figure 2.

Figure 3.

Figure 4.

Figure 5.

Figure 6.

Figure 7.

Figure 8.

【 参考文献 】

• [1]Teoh M, Clark CH, Wood K, Whitaker S, Nisbet A: Volumetric modulated arc therapy: a review of current literature and clinical use in practice. Brit J Radiol 2011, 84:967-996.
• [2]Wolff D, Stieler F, Welzel G, Lorenz F, Abo-Madyan Y, Mai S, Herskind C, Polednik M, Steil V, Wenz F, Lohr F: Volumetric modulated arc therapy (VMAT) vs. serial tomotherapy, step-and-shoot IMRT and 3D-conformal RT for treatment of prostate cancer. Radiother Oncol 2009, 93(2):226-233.
• [3]Palma DA, Verbakel WFAR, Otto K, Senan S: New developments in arc radiation therapy: a review. Canc Treat Rev 2010, 36:393-399.
• [4]Ansbacher W: Three-dimensional portal image-based dose reconstruction in a virtual phantom for rapid evaluation of IMRT plans. Med Phys 2006, 33:3369-3382.
• [5]Mans A, Remeijer P, Olaciregui-Ruiz I, Wendling M, Sonke JJ, Mijnheer B, Van Herk M, Stroom JC: 3D dosimetric verification of volumetric-modulated arc therapy by portal dosimetry. Radiother Oncol 2010, 94:181-187.
• [6]Bailey DW, Kumaraswamy L, Bakhtiari M, Malhotra HK, Podgorsak MB: EPID dosimetry for pretreatment quality assurance with two commercial systems. J Appl Clin Med Phys 2012, 13(2):82-99.
• [7]Van Elmpt W, McDermott L, Nijsten S, Wendling M, Lambin P, Mijnheer B: A literature review of electronic portal imaging for radiotherapy dosimetry. Radiother Oncol 2008, 88:289-309.
• [8]Klein EE, Hanley J, Bayouth J: Quality assurance of medical accelerators. Med Phys 2009, 36:4197-4112.
• [9]McGarry CK, Grattan MWD, Cosgrove VP: Optimization of image quality and dose for Varian aS500 electronic portal imaging devices (EPIDs). Phys Med Biol 2007, 52:6865-6877.
• [10]Du W, Gao S, Wang X, Kudchadker RJ: Quantifying the gantry sag on linear accelerators and introducing an MLC-based compensation strategy. Med Phys 2012, 39(4):2156-2162.
• [11]Grattan MW, McGarry CK: Mechanical characterization of the varian Exact-arm and R-arm support systems for eight aS500 electronic portal imaging devices. Med Phys 2010, 37(4):1707-1713.
• [12]Rowshanfarzad P, Sabet M, O’Connor DJ, Greer PB: Investigation of the sag in linac secondary collimator and MLC carriage during arc deliveries. Phys Med Biol 2012, 57(12):N209-N224.
• [13]Rowshanfarzad P, Sabet M, O’Connor DJ, McCowan PM, McCurdy BMC, Greer PB: Detection and correction for EPID and gantry sag during arc delivery using cine EPID imaging. Med Phys 2012, 39(2):623-635.
• [14][http://webstore.iec.ch/preview/info_iec61217%7Bed2.0%7Db.pdf] webcite International Electrotechnical Commission (IEC): Radiotherapy equipment: coordinates, movements and scales. Report No. IEC 61217. Geneva: IEC; 2008. .
• [15]Rowshanfarzad P, Sabet M, O’Connor DJ, Greer PB: Verification of the linac isocentre for stereotactic radiosurgery using cine-EPID imaging and arc delivery. Med Phys 2011, 38(7):3963-3970.
• [16]Rangel A, Dunscombe P: Tolerances on MLC leaf position accuracy for IMRT delivery with a dynamic MLC. Med Phys 2009, 36:3304-3309.
• [17]Agnew CE, Irvine DM, Hounsell AR, McGarry CK: Improvement in clinical step and shoot intensity modulated radiation therapy delivery accuracy on an integrated linear accelerator control system. Pract Radiat Oncol 2014, 4(1):43-49.
• [18]Varian Medical Systems: TrueBeamTM, TrueBeamSTxTM, Technical reference guide (Version 1.6 Volume 2: Imaging; Docu ID: B501671R01, RevisionD). Switzerland: Varian Medical Systems, Inc; 2011:205–207.
• [19]Gao S, Du W, Balter P, Munro P, Jeung A: Evaluation of IsoCal geometric calibration system for Varian linacs equipped with on-board imager and electronic portal imaging device imaging systems. J Appl Clin Med Phys 2014, 15(3):164-181.
• [20]Liu B, Adamson J, Rodrigues A, Zhou F, Yin FF, Wu Q: A novel technique for VMAT QA with EPID in cine mode on a Varian TrueBeam linac. Phys Med Biol 2013, 58:6683-6700.
• [21]Bakhtiari M, Kumaraswamy L, Bailey DW, de Boer S, Malhotra HK, Podgorsak MB: Using an EPID for patient-specific VMAT quality assurance. Med Phys 2011, 38:1366-1373.
• [22]Chin PW, Lewis DG, Spezi E: Correction for dose–response variations in a scanning liquid ion chamber EPID as a function of linac gantry angle. Phys Med Biol 2004, 49(8):N93-N103.