SU‐E‐P‐44: The Characteristics and Clinical Application of the ArcCHECK for VMAT Verification

Purpose:To evaluate the characteristics and clinical suitability of the ArcCHECK QA system for VMAT verification.Methods:The intrinsic sensitivity,short and long term reproducibility,dose and dose rate dependence,dose per pulsed dependence,field sizes dependence and directional response of the diodes were measured.The results of the diodes were compared with the measurement results of an ionization chamber and calculated results of TPS. Gamma index (3mm distance to agreement and 3% percentage difference ) was used to analyze the dose difference between the calculation and measurement for random selected 211 verified VMAT plans.Results:The ArcCHECK diodes performed well for all tests except directional dependence, which varies from a minimum of −3.9% (seen only when the beam is incident on the diode at 180°) to a maximum of 7.7% (approximately at 255°). Average gamma analysis passing rates with 3mm/3% for 113 NPC,48 cervical cancer and 50 rectal cancer VMAT plans are 93.5%,95.7% and 97.5%, statistical significance has been found between either two of the groups(t=−12.69∼−4.88,all P<0.01).Conclusion:With proposed calibration method,the ArcCHECK QA system is very suitable for VMAT pretreatment verification,the complexity of VMAT plan is the main factor affecting the passing rate.