SU‐C‐105‐03: Progress Toward the Development of a Deformable Anthropomorphic 3D Dosimetric Phantom

Abstract

Purpose: Previous work has demonstrated that Presage‐Def, a deformable, polyurethane‐based radiochromic 3D dosimeter, has strong potential for validating deformable image registration algorithms by tracking optically measured radiation patterns from the deformed shape to the non‐deformed shape. Here we present recent investigations into the efficacy of variant Presage‐Def formulations with a range of elastic properties in terms of increased dose sensitivity and post‐irradiation stability. Methods: Eleven formulations of Presage‐Def were created from combinations of 3 elastic polyurethane matrices (Shore Hardness 10–20A and 30A) and 7 leuco dyes. Dose sensitivity for each formulation was determined by irradiating cuvettes from 0–8Gy and measuring change in optical density at 633nm. Sensitivity readings were tracked over time to determine stability. Complementary to the small volume studies, a 15.7cm diameter cylindrical Presage‐Def deformable dosimeter was created incorporating two air cavities (4.0cm diameter) and a rigid high‐Z spine‐mimic insert (2.8cm diameter). The dosimeter was subjected to bilateral compression to demonstrate complex, non‐uniform deformation, and also irradiated with an 8.6cm×7.4cm field and imaged with optical‐CT to investigate feasibility of optical‐CT dose readout in a heterogeneous phantom. Results: Dose sensitivities ranged from 0.0004‐0.0071ΔOD/(Gy*cm) versus 0.0032ΔOD/(Gy*cm) in the original formulation. Highest sensitivity and stability were both seen in formulation PD1 (#2 polyurethane, leuco dye 1‐napthal‐N,N‐diethylamine LMG), which retained 98.6% initial sensitivity over 4 hours whereas the original dropped to 90.6% after 1 hour. X‐ray CT images of the prototype phantom with and without compression demonstrated non‐uniform deformation of Presage‐Def and air cavity geometry while the rigid region remained constant. The irradiated field was clearly visible in 3D dose distributions obtained by optical‐CT. Conclusion: A Presage‐Def formulation was identified from 10 variants with improved dosimetric characteristics. Optical‐CT dose readout was achieved in the prototype phantom, demonstrating feasibility of 3D dosimetry in a large deformable dosimeter containing air and rigid bone‐mimic inserts. NIH R01CA100835