Polymer gel dosimeter calibration using X-Ray CT imaging.

Abstract

The aim of this work is to study the development of a polymer gel dosimetry system called MAGIC gel (Methacrylic acid and ascorbic acid in copper-initiated gelatin) using X-ray CT (CT-scan) in order to be applied in dosimetry during the 3D simulation of a radiotherapy treatment and to determine the calibration curve describing the performance of this gel as a dosimeter capable of translating the three-dimensional distribution of the irradiation dose. The MAGIC gel was prepared from the formulation proposed by Fong et al. in the literature. (2001) with some modifications. The irradiations of the gel were carried out horizontally using a source of Co. The tubes irradiated with MAGIC gel were evaluated using UV-Vis. The results showed a linear relation between the maximum absorbance and the -absorbed dose ranging from 2 to 14 Gy. After the synthesis and irradiation of the MAGIC gel, a scanner reading dedicated to the CAC-Setif was made for the determination of the calibration curve of this dosimeter in external radiotherapy. The doses used vary between 2 and 14 Gy. The CT protocol for obtaining the best image quality of the irradiated MAGIC gel was determined to evaluate the dose information. CT scanner parameters were 120 kV, 200 mA variation, slice thickness of 6 mm, 5 s exposure time, using a standard resolution and reconstruction algorithm for 25 x 25 cm2. A linear relationship was found approximately between CT numbers the doses between 2 and 15 Gy. The PDD obtained based on measurements with CT was compared to the calculated PDD referenced to the laboratory SSDL based on measurements made with an ionization chamber. Key-words: MAGIC gel, X-ray CT (CT-scan), calibration, 3Ddose distribution