RapidArc™ treatment verification using polymer gel dosimetry

The aim of this study was to verify a novel volumetric arc therapy technique, RapidArc". Polymer gel dosimetry system was used to measure the advanced inhomogeneous 3D dose distribution produced using the technique RapidArc". A preclinical installation of the novel beam delivery approach was set up on a linear accelerator at Rigshospitalet in Copenhagen. A prostate treatment plan was delivered to a 1.3 l nPAG gel phantom using one single arc rotation from 200 to 160 degrees, and a target dose of 3.3 Gy. Magnetic resonance imaging of the gel was carried out using the 1.5 T scanner and MATLAB was used for image processing and 3D rendering. The difference in relative absorbed dose between the treatment planning system (TPS) and gel measurement was calculated voxel by voxel within the 80% and the 95% isodose volume, respectively. Measurements agreed well with the TPS within the treated volume. Within both isodose volumes 90% of the voxels showed a deviation less or equal to 5%. This study shows that the 3D gel dosimetry system is a useful tool for dose verification of advanced treatment delivery techniques