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 u 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 u . 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 22.46 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. The concept of volumetric modulated arc therapy (VMAT) has been described in many studies [1][2][3][4][5]. VMAT is a system for intensity-modulated radiotherapy treatment (IMRT) delivery that achieves high dose conformity by optimising the dose rate, gantry speed and leaf positions of the dynamic multileaf collimator (MLC) [6]. One study [5] demonstrated quality assurance (QA) checks using dynamic MLC controller log files (Dynalog) for VMAT systems such as RapidArcH (Varian Medical Systems Inc., Palo Alto, CA). It is assumed that the actual delivery process is truly represented in the log files [6]. The major disadvantage of this method is that Dynalog files need to be validated against an independent system. The electronic portal imaging device (EPID) is a dependable system when corrections are made for systematic tilts and shifts [7,8] and when image sagging due to gantry angle [9] has been taken into account. A significant number of researchers have investigated MLC QA by film or EPID [7][8][9][10][11][12][13] to measure the accuracy of the MLC controller independently and ensure that the MLC edge positions agree with the radiation field edges to within 0.3 mm [14]. EPID measurements are highly reproducible, with a standard deviation of ,0.1 mm for individual leaf/collimator positions and ,0.05 mm for a 10610 cm 2 field [7]. Few studies [15][16][17] have demonstrated commissioning, QA and patient-specific QA for VMAT using both the RapidArc and the SynergyH S (Elekta, Stockholm, Sweden) systems. The purpose of this study was to demonstrate QA checks for accuracy of gantry...

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For high dose rate (HDR) brachytherapy, independent treatment verification is needed to ensure that the treatment is performed as per prescription. This study demonstrates dosimetric quality assurance of the HDR brachytherapy using a commercially available two-dimensional ion chamber array called IMatriXX, which has a detector separation of 0.7619 cm. The reference isodose length, step size, and source dwell positional accuracy were verified. A total of 24 dwell positions, which were verified for positional accuracy gave a total error (systematic and random) of –0.45 mm, with a standard deviation of 1.01 mm and maximum error of 1.8 mm. Using a step size of 5 mm, reference isodose length (the length of 100% isodose line) was verified for single and multiple catheters of same and different source loadings. An error ≤1 mm was measured in 57% of tests analyzed. Step size verification for 2, 3, 4, and 5 cm was performed and 70% of the step size errors were below 1 mm, with maximum of 1.2 mm. The step size ≤1 cm could not be verified by the IMatriXX as it could not resolve the peaks in dose profile.

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