A feasibility study of a gelatin-based tissue substitute

Abstract

Estimates of internal radiation dose require, among other parameters, values of absorbed fraction (AF) for the source and target organs under consideration. These values are generally obtained through Monte Carlo simulation. Computational estimates of absorbed fractions, however, are subject to limitations including statistical uncertainty due to sampling variation and the adequacy of the mathematical model representing the physical system of interest. Consequently, experimental verification of Monte Carlo results is often desired. A feasibility study was conducted in which several tissue substitutes were evaluated for their potential use as volumetric dosimeters. In order to be considered in this study, a given material had to approximate the tissue of Reference Man as specified in Publication 23 of the International Commission on Radiological Protection. This evaluation was based on the electron stopping power, the mass attenuation coefficient, the electron mass density, and the specific gravity. Another important criteria was that the tissue substitute had to be capable of changing from a liquid into a solid form to facilitate an even distribution of thermoluminesent dosimetry (TLD) powder throughout the mold. Secondly, it had to reliquify rather easily to allow for recovery of the TLD powder with little or no loss of thermoluminesence. Of the three materials selected for evaluation, a 10% gelatin mixture provided the closest match to Reference Man tissue. The gelatin mixture was put through a series of tests to determine the usefulness as a reliable tissue substitute. The TLD powder was cast in the gelatin mixture and recovered to determine if the TLD powder was adversely affected. The distribution of the TLD powder cast into the gelatin mixture was tested to ensure an even distribution of powder was maintained throughout the mold. The gelatin was easily changed from a liquid state to a solid state which could support an even distribution of the TLD powder. Recovery of the TLD was performed with relative ease and showed minimal loss of thermoluminescence in the recovered powder. It was therefore determined that the gelatin mixture was a suitable tissue-equivalent substitute to be used in volumetric dosimetry studies.