Evaluation of a complementary metal oxide semiconductor detector as a tool for stereotactic body radiotherapy plan quality assurance.

Abstract

A sub-mm resolution Complementary Metal Oxide Semiconductor sensor has been developed for stereotactic radiotherapy quality assurance. Herein we evaluate its basic dosimetric performance and its application for linac C-arm stereotactic body radiotherapy (SBRT) plan quality assurance. The detector was integrated into its accompanying phantom or in Water Equivalent Plastic (WEP). The measurement reproducibility, stability, dose linearity and dependence on angularity, dose rate and field size were investigated. Clinical plan measurements were compared to our radiotherapy treatment planning system and radiochromic film. Sensitivity to introduced Multi Leaf Collimator (MLC) offsets was evaluated by simulating single MLC offsets in SBRT plans and comparing measurements to expected doses. Signal reproducibility was within±0.1% and output calibration was stable over a 6month period. Detector showed good linearity with dose (r2=1). Signal decreased by 5% when dose rate was decreased from 1300 MU/min to 300 MU/min. Output factors agreed within 0.5% of chamber measurements for 1x1 cm field sizes or greater. Angularity measurements showed good agreement with reference. For measurement of planned clinical doses, gamma pass-rates were 98.5%±2.3% (treatment planning system reference, 2%/2mm) and 99.2%±1.0% (film reference, 2%,2mm). The detector also showed sensitivity to errors of 1mm offsets in MLC positioning. The detector performed well when used for pre-treatment SBRT plan quality assurance, offering a good alternative to radiochromic film.