VMAT linear accelerator commissioning and quality assurance: dose control and gantry speed tests.

VMAT linear accelerator commissioning and quality assurance: dose control and gantry speed tests.
J Appl Clin Med Phys. 2016;17(3):6067
Authors: Barnes MP, Rowshanfarzad P, Greer PB
Abstract
In VMAT treatment delivery the ability of the linear accelerator (linac) to accurately control dose versus gantry angle is critical to delivering the plan correctly. A new VMAT test delivery was developed to specifically test the dose versus gantry angle with the full range of allowed gantry speeds and dose rates. The gantry-mounted IBA MatriXX with attached inclinometer was used in movie mode to measure the instantaneous relative dose versus gantry angle during the plan every 0.54 s. The results were compared to the expected relative dose at each gantry angle calculated from the plan. The same dataset was also used to compare the instantaneous gan-try speeds throughout the delivery compared to the expected gantry speeds from the plan. Measurements performed across four linacs generally show agreement between measurement and plan to within 1.5% in the constant dose rate regions and dose rate modulation within 0.1 s of the plan. Instantaneous gantry speed was measured to be within 0.11°/s of the plan (1 SD). An error in one linac was detected in that the nominal gantry speed was incorrectly calibrated. This test provides a practical method to quality-assure critical aspects of VMAT delivery including dose versus gantry angle and gantry speed cont...

Source: Journal of Applied Clinical Medical Physics - May 15, 2016 Category: Physics Authors: Barnes MP, Rowshanfarzad P, Greer PB Tags: J Appl Clin Med Phys Source Type: research