Evaluation of a 2D detector array for patient-specific VMAT QA with different setups

For pre-treatment plan verification of advanced treatment techniques such as intensity-modulated arc therapy, a fast and reliable dosimetric device is required. In this study, we investigated the suitability of MatriXX in different setups for verification of volumetric modulated arc therapy (VMAT) plans. If MatriXX is used in a stationary phantom (MULTICube), the measured dose is dependent on the beam angle. For the first setup (MatriXX/MULTICube), we developed correction factors (CFs) for each detector element (1020 CFs). We investigated the accuracy of these CFs by verifying 12 VMAT plans. In the second setup, we also assessed the suitability of MatriXX in a dedicated holder. Using this setup (MatriXX/Holder), 30 additional VMAT plans were verified. Deviations of up to similar to 17% and similar to 11% were noted for one of the ion chambers at 90 degrees and 180 degrees gantry positions. The influence of the beam angle dependence (MULTICube) can explicitly be seen when a gamma criterion of 2%/2 mm was chosen. An overall improvement of 4.3% of passing pixels (pp) was noted after applying beam angular-dependent CFs. When the gamma criterion was 3%/3 mm, the %pp was >= 95% without and similar to 100% with correction. With the second setup, MatriXX/holder, we showed excellent agreement between measurements and calculations. The % pp averaged over all plans (30 VMAT treatment plans) was nearly similar to 100%. The combination of MatriXX with MULTICube or with holder proved to be a fast and reliable method for pretreatment verification of arc therapy with sufficient accuracy.