ESTRO 2025 - Abstract Book

S2587

Physics - Detectors, dose measurement and phantoms

ESTRO 2025

1885

Digital Poster Dosimetric response of radiochromic materials as a function of alkyl chain length Rohith Kaiyum 1,2 , Ozzy Mermut 1,3 , Alexandra Rink 2,4,5

1 Physics and Astronomy, York University, Toronto, Canada. 2 Medical Physics, University Health Network, Toronto, Canada. 3 Chemistry, York University, Toronto, Canada. 4 Radiation Oncology, University of Toronto, Toronto, Canada. 5 Medical Biophysics, University of Toronto, Toronto, Canada Purpose/Objective: Research on radiochromic dosimeters has centered on commercially available products like Gafchromic MD-55 and EBT-3 (both using 10,12-Pentacosadiynoic acid (PCDA) or its salt as the active component) 1,2 , with little attention to the underlying chemical mechanisms affecting dosimetry. In this study, we explore how the alkyl chain length impacts the dose response of custom diacetylene-based radiochromic dosimeters designed for real-time dosimetry applications. We hypothesize that the dose sensitivity increases with alkyl chain length due to hydrogen bonding between monomers. Material/Methods: Radiochromic solutions were prepared using 10,12-Octadecadiynoic acid (OCDA), 10,12-Tricosadiynoic acid (TCDA) and PCDA which have a 5, 10 and 12 carbon alkyl chain attached to the diacetylene. The radiochromic solutions prepared in 10% gelatin were coated between two sheets of polyethylene forming films with active material thickness of ~ 100-130 µm. Samples (N=5 at each dose and crystal) were irradiated to 0-2000 cGy (Varian TrueBeam, 6 MV, 100 cm SAD, 1.5 cm depth, 10 x 10 field size) within a custom phantom equipped with optical fibers, enabling real-time measurements of absorbance spectra and optical density (ΔOD) 3 .The absorbance spectra were collected (OceanOptics USB4000) at 1Hz and ΔOD was calculated using a10 nm band around the main absorbance peak as a function of time. The ΔOD at end of beam, characterized by an inflection point, was used for the calibration curves. Sample thickness was measured prior to irradiation using a digital caliper and used to normalize the calibration curves to the average thickness of all irradiated samples (~109 µm). Normalized calibration curves were fit to a linear model and relative % dose sensitivity of OCDA and TCDA were determined relative to PCDA. Results: All of the radiochromic formulations had a detectable dose response and their calibration curves could be sufficiently described by a linear model with adjusted R 2 ~ 0.99. Despite having a significantly shorter alkyl chain length compared to TCDA, OCDA had a higher dose response; however, PCDA, which has only 2 more carbons than TCDA, has the highest overall dose response. When compared to PCDA, OCDA and TCDA have a % relative sensitivity of 26% and 17% respectively.