Abstract
PurposeThis study investigated the use of high spatial resolution solid‐state detectors (DUO and Octa) combined with an inclinometer for machine‐based quality assurance (QA) of Volumetric Modulated Arc Therapy (VMAT) with flattened and flattening filter‐free beams.MethodThe proposed system was inserted in the accessory tray of the gantry head of a Varian 21iX Clinac and a Truebeam linear accelerator. Mutual dependence of the dose rate (DR) and gantry speed (GS) was assessed using the standard Varian customer acceptance plan (CAP). The multi‐leaf collimator (MLC) leaf speed was evaluated under static gantry conditions in directions parallel and orthogonal to gravity as well as under dynamic gantry conditions. Measurements were compared to machine log files.ResultsDR and GS as a function of gantry angle were reconstructed using the DUO/inclinometer and in agreement to within 1% with the machine log files in the sectors of constant DR and GS. The MLC leaf speeds agreed with the nominal speeds and those extracted from the machine log files to within 0.03 cm s−1. The effect of gravity on the leaf motion was only observed when the leaves traveled faster than the nominal maximum velocity stated by the vendor. Under dynamic gantry conditions, MLC leaf speeds ranging between 0.33 and 1.42 cm s−1 were evaluated. Comparing the average MLC leaf speeds with the machine log files found differences between 0.9% and 5.7%, with the largest discrepancy occurring under conditions of fastest leaf velocity, lowest DR and lowest detector signal.ConclusionsThe investigation on the use of solid‐state detectors in combination with an inclinometer has demonstrated the capability to provide efficient and independent verification of DR, GS, and MLC leaf speed during dynamic VMAT delivery. Good agreement with machine log files suggests the detector/inclinometer system is a useful tool for machine‐specific VMAT QA.
Highlights
Volumetric Modulated Arc Therapy (VMAT) is an extension of Intensity Modulated Radiation Therapy (IMRT)
Purpose: This study investigated the use of high spatial resolution solid‐state detectors (DUO and Octa) combined with an inclinometer for machine‐based quality assurance (QA) of Volumetric Modulated Arc Therapy (VMAT) with flattened and flattening filter‐free beams
We report on the use of a high spatial resolution (0.2 mm) solid‐state detector (DUO), operated in transmission mode which records the current generated in each pixel by the flux of photons and combined to an inclinometer to provide an independent measurement of the angular position of the gantry
Summary
Volumetric Modulated Arc Therapy (VMAT) is an extension of Intensity Modulated Radiation Therapy (IMRT). Electronic portal imaging devices (EPIDs) have become a standard component in the current linac designs.[10,11] Commercial amorphous‐silicon EPIDs have a pixel size of 0.392 mm2 × 0.392 mm[2] and spatial resolution of 0.784 mm.[12,13] Recently, an EPID‐ based system[14] has been tested for VMAT QA This system showed good agreement with a plan for all dynamic parameters including MLC motion, the readout of gantry angle information extracted from the On‐Board Imaging system may not be considered as machine‐independent. That in combination with the easy setup and simple calibration procedure provides a device with the capability to simplify the application of the CoP and its use in clinical practice over existing commercial designs.[25,26,27]
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