Evaluation of a novel N-(Hydroxymethyl) acrylamide polymer gel dosimeter formulation with organic glucose additive for radiotherapy

Abstract

In this study, the first evaluation of organic sensitizer material on N-(Hydroxymethyl) acrylamide (NHMA) polymer gel dosimeter was presented. A novel tissue-equivalent polymer gel formula composed of NHMA containing different concentrations of organic glucose additive (GL-NHMA) was developed and evaluated for its potential use to measure 3D dose distributions to compare with treatment planning system. The new polymers of GL-NHMA were irradiated using a linear accelerator (LINAC) with a megavolt X-ray photon beam over a dose range of 2–20 Gy, energies of 6, 10, and 15 MV, and dose rates of 50, 200, and 500 cGy/min. The samples were evaluated using 0.5 T nuclear magnetic resonance (NMR) technique in terms of spin-spin relaxation rate (R2). Comparing with the conventional NHMA composition (i.e., 0 wt% GL concentration), the sensitivity of the GL-NHAM was improved by 53%, 68%, 89%, and 115% with 10, 15, 20, and 25 wt% GL, respectively, with an excellent linear dose response up to 8 Gy. There were no observable effects on the R2 dose response induced by varying the dose rate, photon energy, and irradiation temperature. The polymerization was stable after irradiation for a period of 10 days. Additionally, the R2 values decreased with increasing the scanning temperature. The dosimeter is water equivalent and is energy-independent from 0.1 to 20 MeV when considering the optimum composition. The gel dosimetry accuracy was evaluated in this study by calculating the overall uncertainty and found to be 4.64% (2σ, 95% confidence level). The GL additive acts as an excellent organic sensitizer in the GL-NHMA system, suggesting that this improved polymer formulation may be a useful tool for measuring dose distributions in radiotherapy at clinically relevant dose levels.