Intrinsic Active Material Calibration of Copper-Based Diacetylene Formulations
Abstract
Purpose
Small variations in radiochromic material thickness in films leads to variability in sensitivity and uncertainty in measured dose. To achieve high accuracy, the commercial films correct for this through a dispersion of the yellow dye, which acts to correct for sensitivity through thickness as a surrogate. Here, we evaluate copper pentacosa-10,12-diynoate (CuPCDA) as a dosimetric material, using its intrinsic green colouration from Cu as an integrated calibrant.
Methods
We manufactured and coated CuPCDA formulations at varying thicknesses, representing different amounts of sensitive material. The coatings were irradiated with 6 MV (Varian TrueBeam) photon beam (1500 cGy, 300 cGy/min, 1.5 cm depth, 100 cm SAD, 10x10 field) in a custom phantom with integrated optical fibers. Absorbance spectra were recorded over 560-740 nm range and radiation-induced change in optical density (ΔOD) at ~600 nm was measured immediately at the end of radiation. Intrinsic absorbance was calculated to generate a calibration curve relating optical signal to deposition thickness. Depositions were evaluated to assess thickness-dependent dose response, and efficacy of intrinsic calibrant.
Results
ΔOD of CuPCDA showed a linear response with dose. ΔOD obtained after 1500 cGy showed an increase with both deposition thickness, and more importantly with Cu-based intrinsic absorption. Integrated absorbance of CuPCDA active component demonstrated a linear relationship with dose response over the investigated range (R2 = 0.8806), supporting its use as a dosimetric calibrant. The change in optical density of CuPCDA coatings was 0.0016 ± 0.0002 per micron, and was comparable to PCDA, the active material in the MD-55 commercial series.
Conclusion
CuPCDA materials are a promising material for a variety of dosimetric applications due to their reasonable sensitivity, linear dose response, and opportunity for intrinsic optical calibration linking radiochromic film sensitivity directly to the amount of active material, rather than a surrogate like deposition thickness.