Aim: This study evaluates the impacts of using different evaluation criteria on gamma pass rates in two commercially available QA methods employed for the verification of VMAT plans using different hypothetical planning target volumes (PTVs) and anatomical regions.
Introduction: Volumetric modulated arc therapy (VMAT) is a widely accepted technique to deliver highly conformal treatment in a very efficient manner. As their level of complexity is high in comparison to intensity-modulated radiotherapy (IMRT), the implementation of stringent quality assurance (QA) before treatment delivery is of paramount importance.
Material and Methods: Two sets of VMAT plans were generated using Eclipse planning systems, one with five different complex hypothetical three-dimensional PTVs and one including three anatomical regions. The verification of these plans was performed using a MatriXX ionization chamber array embedded inside a MultiCube phantom and a Varian EPID dosimetric system attached to a Clinac iX. The plans were evaluated based on the 3%/3 mm, 2%/2 mm, and 1%/1 mm global gamma criteria and with three low-dose threshold values (0%, 10%, and 20%).
Results: The gamma pass rates were above 95% in all VMAT plans, when the 3%/3mm gamma criterion was used and no threshold was applied. In both systems, the pass rates decreased as the criteria become stricter. Higher pass rates were observed when no threshold was applied and they tended to decrease for 10% and 20% thresholds.
Conclusion: The results confirm the suitability of the equipments used and the validity of the plans. The study also confirmed that the threshold settings greatly affect the gamma pass rates, especially for lower gamma criteria.
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 Verbakel WF, Cuijpers J P, Hoffmans D, et al. Volumetric intensity-modulated arc therapy versus conventional IMRT in head-and-neck cancer: a comparative planning and dosimetric study. Int J Radiat Oncol Biol Phys. 2009;74(1):252–259.
 Wolff D, Stieler F, Welzel G, et al. Volumetric modulated arc therapy (VMAT) versus serial tomotherapy, step-and-shoot IMRT and 3D-conformal RT for treatment of prostate cancer. Radiother Oncol. 2009;93(2):226–233.
 Otto K. Volumetric modulated arc therapy: IMRT in a single gantry arc. Med Phys. 2008;35(1):310-317.
 Bedford JL, Warrington AP. Commissioning of volumetric modulated arc therapy (VMAT). Int J Radiat Oncol Biol Phys. 2009;73:537-545.
 Tatsumi D, Hosono MN, Nakada R, et al. 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(20):237-246.
 Pardo Montero J, Fenwick JD. The effect of different control point sampling sequences on convergence of VMAT inverse planning Phys Med Biol. 2011;56(8):2569-2583.
 Iftimia I, Cirino ET, Xiong L, Mower HW. Quality assurance methodology for Varian RapidArc treatment plans. J Appl Clin Med Phys. 2010;11(4):3164
 Chandraraj V, Stathakis S, Manickam R, et al. Consistency and reproducibility of the VMAT plan delivery using three independent validation methods. J Appl Clin Med Phys. 2010;12(1):3373.
 Hussein M, Adams EJ, Jordan TJ, et al. A critical evaluation of the PTW 2D-ARRAY seven29 and OCTAVIUS II phantom for IMRT and VMAT verification. J Appl Clin Med Phys. 2013;14(6):4460.
 Zhu J, Chen L, Jin G. A comparison of VMAT dosimetric verifications between fixed and rotating gantry positions. Phys Med Biol. 2013;58(15):1315-1322.
 Wolfsberger LD, Wagar M, Nitsch P, et al. Angular dose dependence of Matrixx TM and its calibration J Appl Clin Med Phys. 2010;11(1): 241-251.
 Herzen J, Todorovic M, Cremers F, et al. Dosimetric evaluation of a 2D pixel ionization chamber for implementation in clinical routine Phys Med Biol. 2007;52(4):1197-1208.
 Li JG, Yan G, Liu C. Comparison of two commercial detector arrays for IMRT quality assurance J Appl Clin Med Phys. 2009;10(2):62-74.
 Han Z, Ng SK, Bhagwat MS, et al. Evaluation of MatriXX for IMRT and VMAT dose verifications in peripheral dose regions. Med Phys. 2010;37(7):3704-3714.
 Wiezorek T, Banz N, Schwedas M, et al. Dosimetric quality assurance for intensity-modulated radiotherapy feasibility study for a filmless approach. Strahlenther Onkol. 2005;181(7):468-474.
 Chandraraj V, Stathakis S, Manickam R, et al. Comparison of four commercial devices for RapidArc and sliding window IMRT QA. J Appl Clin Med Phys. 2011;12(2):338-349.
 Shimohigashi Y, Araki F, Tominaga H, et al. Angular dependence correction of MatriXX and its application to composite dose verification. J Appl Clin Med Phys. 2012;13(5):81-96.
 Boggula R, Birkner M, Lohr F, et al. Evaluation of a 2D detector array for patient-specific VMAT QA with different setups. Phys Med Biol. 2011l56(22):7163-7177.
 Bakhtiari M, Kumaraswamy L, Bailey DW, et al. Using an EPID for patient-specific VMAT quality assurance Using an EPID for patient-specific VMAT quality assurance. Med Phys. 2011;38(3):1366-73.
 Iori M, Cagni E, Paiusco M, et al. Dosimetric verification of IMAT delivery with a conventional EPID system and a commercial portal dose image prediction tool. Med Phys. 2010;37(1):377-390.
 Sharma DS, Mhatre V, Heigrujam M, et al. Portal dosimetry for pretreatment verification of IMRT plan : a comparison with 2D ion chamber array. J Appl Clin Med Phys. 2010;11(4):3268.
 Low DA, Harms WB, Mutic S, Purdy JA. A technique for the quantitative evaluation of dose distributions. Med Phys. 1998;25(5):656-661.
 Bailey DW, Nelms BE, Attwood K, et al. Statistical variability and confidence intervals for planar dose QA pass rates. Med Phys. 2011;38(11):6053-6064.
 Low DA, Dempsey JF. Evaluation of the gamma dose distribution comparison method. Med Phys. 2003;30(9):2455-2464.
 Das IJ, Ding GX, Ahnesjö A. Small fields: nonequilibrium radiation dosimetry. Med Phys. 2008;35(1):206-215.
 Bailey DW, Kumaraswamy L, Bakhtiari M, et al. EPID dosimetry for pretreatment quality assurance with two commercial systems. J Appl Clin Med Phys. 2012;13(4):3736.
 Wagner D, Vorwerk H. Two years experience with quality assurance protocol for patient related Rapid Arc treatment plan verification using a two dimensional ionization chamber array. Radiat Oncol. 2011;6(1):21.
 Mans A, Remeijer P, Olaciregui-Ruiz I, et al. 3D dosimetric verification of volumetric-modulated arc therapy by portal dosimetry. Radiother Oncol. 2010;94:181-187.
 van Elmpt W, Nijsten S, Dekker AL, et al. Treatment verification in the presence of inhomogeneities using EPID-based three dimensional dose reconstruction Med. Phys. 2007;34(7):2816-2826.
 Boggula R, Lorenz F, Mueller L, et al. Experimental validation of a commercial 3D dose verification system for intensity-modulated arc therapies. Phys Med Biol. 2010;55(19):5619-5633.
 Mancuso GM, Fontenot JD, Gibbons JP, parker BC. Comparison of action levels for patient-specific quality assurance of intensity modulated radiation therapy and volumetric modulated arc therapy treatments. Med Phys. 2012;39(7):4378-4385.