Radiological tissue equivalence of deformable silicone-based chemical radiation dosimeters (FlexyDos3D)

FlexyDos3D, a silicone-based chemical radiation dosimeter, has great potential to serve as a three-dimensional (3D) deformable dosimetric tool to verify complex dose distributions delivered by modern radiotherapy techniques. To facilitate its clinical application, its radiological tissue needs to be clarified. In this study we investigated its tissue-equivalence in comparison with water and Solid Water (RMI457). We found that its effective and mean atomic numbers were 40% and 20% higher and the total interaction probabilities for kV x-ray photons were larger than those of water respectively. To assess the influence of its over-response to kV photons, its HU value was measured by kV computed tomography (CT) and was found higher than all the soft-tissue substitutes. When applied for dose calculation without correction, this effect led to an 8% overestimation in electron density via HU-value mapping and 0.65% underestimation in target dose. Furthermore, depth dose curves (PDDs) and off-axis ratios (profiles) at various beam conditions as well as the dose distribution of a full-arc VMAT plan in FlexyDos3D and reference materials were simulated by Monte Carlo, where the results showed great agreement. As indicated, FlexyDos3D exhibits excellent radiological water-equivalence for clinical MV x-ray dosimetry, while its nonwater-equivalent effect for low energy x-ray dosimetry requires necessary correction. The key findings of this study provide pertinent reference for further FlexyDos3D characterization research.