Comprehensive characterisation of the IBA myQA SRS Detector for SRS and SBRT patient specific quality assurance

Abstract

Abstract The IBA myQA SRS device is a new to market 2D CMOS detector array with an active area 140x120 mm2 and 0.4 mm resolution, making it a potential real-time dosimetry alternative to film verification for stereotactic plan verifications. Characterisation of the device was performed to assess performance. The devices dosimetric properties were measured for 6X and 6FFF beams from a Varian TrueBeam STx with HD-MLC. Clinical suitability of the device for PSQA was verified using ten SRS/SBRT plans, compared against other detectors, as well as MLC tests including picket fence and chair. Gamma analysis was performed using myQA software with criteria of 4%/1mm. The device demonstrated compliance with recommended specifications for basic tests. After the required warm-up period, the maximum deviation in detector signal from initial readings was 0.2%. Short-term and long-term reproducibility was 0.1%(6X) and 1%(6FFF), respectively. Dose linearity was within 0.3%(6X) and 0.7%(6FFF) and dose-rate dependence within 1.70%(6X), and 2.93%(6FFF) compared to ionization chamber measurements. Angular dependence was quantified for coplanar and non-coplanar situations. Output factors and beam profiles showed agreements within 1% with the CC04 and CC13 chambers for field sizes 1x1 to 10x10cm2. The minimum gamma (4%/1mm) pass rates for MLC-pattern tests were 96% and 98% for the myQA SRS device and film, respectively. The average gamma (4%/1mm) pass rates for SBRT and SRS plans were 98.8% and 99.8% respectively. This work represents one of the first studies performed on the commissioning and performance characterisation of this novel device, demonstrating its accuracy and reliability, making it highly useful as a film alternative in stereotactic treatment plan verification.