Microscopic SEM Texture Analysis of NIPAM Gel Dosimeters

Abstract

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 50t, 500ntn and 3500t , 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 500t and 3500t magnification showed significant changes in morphological features of the irradiated gel. The r2 of the linear fitting from 3500t 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.