Improved recipes for leuco-crystal violet micelle gel dosimeters

Abstract

An optimized recipe for a radiochromic micelle (RM) leuco-crystal violet (LCV) gel dosimeter was proposed using full-factorial designed experiments and model-based optimization. Linear regression models were used to optimize gel recipes with regard to high dose sensitivity (DS) and minimal dose-rate dependence. The proposed gel recipe contains 35 mM cetyltrimethylammonium bromide (CTAB), 1.10 mM LCV, 173 mM 2,2,2-trichloroethanol (TCE), 25 mM trichloroacetic acid (TCAA), 96 wt% water and 4 wt% gelatin. Results from replicate cuvette experiments showed that the proposed gel recipe is dose-rate independent and has an average DS equal to 0.0141 Gy-1 cm-1. No statistically significant energy-dependence was observed in cuvette experiments involving 12 MeV electrons and 6 MV photons. Preliminary 3-D dosimetry experiments were conducted in 1 L jars to study dose responses of the proposed recipe in large phantoms. The DS was 0.0110 Gy-1 cm-1 for a 1 L phantom irradiated with 12 MeV electrons, and 0.0115 Gy-1 cm-1 for a 1 L phantom irradiated with 6 MV photons. Further work on 1 L phantoms is required to test gel reproducibility and the statistical significance of any dose-rate dependent or energy-dependent behavior. A systematic study was performed testing the reusability and reproducibility of the optimized gel recipe. A large batch of gel material was made from replicates that were previously irradiated to doses up to 30 Gy. Three iterations of gel re-use were performed to study the effects of gel dosimeter recycling on initial background colour, DS and dose-rate-dependence. A statistically significant linear increase in background colour suggests that the proposed gel dosimeter might be suitable for storing and administering incremental radiation doses. An apparent upward trend in DS with gel re-use was observed, which suggests that RM LCV gel dosimeters could benefit from a pre-irradiation step to help improve dosimeter sensitivity. Minor dose-rate dependent behavior was observed after multiple gel re-uses; however, no significant behavior was observed at the 95% confidence level. Additional testing on 1 L phantoms is required to determine the clinical relevance and reusability potential of the proposed gel dosimeter.