Microscopic SEM Texture Analysis of NIPAM Gel Dosimeters

Polymer gel dosimeters have been proved as a useful tool in the verification of treatment planning for three-dimensional radiation therapy. The degree of radiation-induced polymerization (DP) is a function of absorbed dose, and it can be determined in macro-scale by several imaging modalities, such as magnetic resonance imaging (MRI), optical computed tomography, and computed tomography (CT). In this study, we determined the DP for the polymer gel dosimeter in micro-scale by texture analysis on scanning electron microscope (SEM) images. The irradiated n-NIPAM gels with absorbed doses of 5 to 20 Gy delivered by the linear accelerator were freeze-dried and sliced. The SEM images were acquired at magnification of 50×, 500 ×  and 3500× , respectively. Four image texture indices, including the entropy, contrast, energy and homogeneity, were estimated from the grey level co-occurrence matrix of each SEM image. The relationships between the radiation dose and texture indices were determined. The SEM images with 500× and 3500× magnification showed significant changes in morphological features of the irradiated gel. The r² of the linear fitting from 3500× SEM images was 0.8194 (entropy), 0.6024 (contrast), 0.7681 (energy), and 0.9978 (homogeneity), respectively. We conclude that the texture analysis on SEM images is a feasible method to estimate the dose response of the polymer gel dosimeter.