An investigation into the robustness of Optical-CT dosimetry of a radiochromic dosimeter compatible with the RPC Head-and-Neck Phantom

The potential of the PRESAGE/Optical-CT system as a comprehensive 3D dosimetry tool has been demonstrated. The current study focused on detailed characterization of robustness (intra-dosimeter uniformity and temporal stability) and reproducibility (inter-dosimeter reproducibility) of PRESAGE inserts compatible with the RPC H and N phantom. In addition, the accuracy and precision of PRESAGE dose measurement was also evaluated. Four identical PRESAGE dosimeters (10cm diameter and 7cm height cylinders) were irradiated with the same rotationally symmetric treatment plan using a Varian accelerator. The treatment plan was designed to rigorously evaluate robustness and reproducibility for multiple dose levels and in 3D. All dosimeters were scanned by optical-CT at daily intervals to study temporal stability. Dose comparisons were made between PRESAGE, ECLIPSE, and independent measurement with EBT film at a select depth. The use of improved optics and acquisition technique yielded substantially higher quality 3D dosimetry data from PRESAGE than has been achieved previously (noise reduced to ∼1%, accuracy to within 3%). Data analysis showed excellent intra-dosimeter uniformity, temporal stability and inter-dosimeter reproducibility of relative radiochromic response. In general, the PRESAGE dose-distribution was found to agree better with EBT (∼99% pass rate) than with ECLIPSE calculations (∼92% pass rate) especially in penumbral regions for a 3% dose-difference and 3 mm distance-to-agreement evaluation criteria. The results demonstrate excellent robustness and reproducibility of the PRESAGE for relative 3D-dosimetry and represent a significant step towards incorporation in the RadOnc-clinic (e.g. integration with RPC phantom).