Utilisation des gels de polymères MAGIC pour la dosimétrie d’une source non scellée d’yttrium 90

Abstract

Polymer gels are relative chemical dosimeters. They allow to access to three-dimensional dose distribution. The aim of this study has been to investigate the preparation and the use of a polymer gel with a tissue equivalent density known as MAGIC gel from magnetic resonance imaging and x-ray computed tomography for non-sealed source dosimetry. This kind of gel is “normoxic” because it can be manufactured and used in normal room atmosphere. In the first part of this study, its accuracy and sensibility were studied using external beam irradiation by photons. Spin-spin relaxation rate ( R 2) and Computed Tomography (CT) number had been used to record gel responses. Using the same manufacture process, radiolabelled gels composed of 95% MAGIC gel and 5% of 90Y termed 90Y-MAGIC 95, with varying activity ranged from 0 to 30 MBq were made. In case of photon external beam irradiation, a linear response is observed whatever the calibration method and the imaging system used (the correlation coefficient r 2 > 0.98 in all cases). 90Y-MAGIC 95 radiolabelled gel responses were recorded after 28, 76 and 124 h. The R 2/dose curves are not linear; three phases can be described, the first being linear with a slow slope (0.14 s −1 Gy −1 instead of 0.41 s −1 Gy −1 for external beam irradiation of the same gel batch). This study shows safety of radiolabelled MAGIC gels manufacturing process and their large dosimetric feasibility. 90Y-MAGIC 95 gel response appears to be reproducible and related to the absorbed dose, thus this gel is a promising tool for non-sealed source dosimetry.