Comparison of Arccheck and Portal Dosimetry in dose Verification for Intensity Modulated Radiotherapy (IMRT) and Rapidarc Plans

This study compares Portal Dosimetry with the ArcCheck phantom for patient-specific QA of RapidArc and IMRT plans. The Electronic Portal Imaging Device (EPID) from Varian and the Eclipse Treatment Planning System (TPS) were used for portal dosimetry, while the ArcCheck cylindrical phantom from Sun Nuclear was used for phantom studies. Eclipse-TPS facilitated RapidArc and dynamic IMRT treatment planning and portal dosimetry (PD) for planar dose calculations. Two verification plans were created for each of the 12 patient plans, totaling 24 arcs delivered on two QA systems. The 12 plans, each with two arcs, were delivered on the EPID of the Varian TrueBeam Linac and the ArcCheck phantom. Planar dose matrices were analyzed using the global Gamma Index criteria of 2mm DTA and 2% dose difference. Measurements were performed using the Varian TrueBeam Linac mounted EPID (aS1200) with Portal dosimetry and the ArcCheck phantom with its software. The QA results from both methods were evaluated and compared. The maximum deviations of dose points (γ>1) were 2.9% and 2.2 CU in the ArcCheck phantom and Portal dosimetry, respectively. Mean and standard deviation values were lower in portal dosimetry than in phantom studies, attributed to the closely embedded chambers in the EPID compared to the detector spacing in the phantom. Both dosimetric QA systems are suitable for patient-specific QA of RapidArc or VMAT and IMRT treatments. With a 2%/2mm criterion, the average γ passing rates were over 98% for PD and over 95% for ArcCheck, with PD showing slightly higher consistency.