Pages: 242-249

Authors: Salvatore Gallo, Giorgio Collura, Giuseppina Iacoviello, Anna Longo, Luigi Tranchina, Antonio Bartolotta, Francesco d'Errico, and Maurizio Marrale

Abstract

This work describes the preliminary analysis of Fricke gels dosimeters characterized by a new formulation making use of a matrix of polyvinyl alcohol cross-linked by adding glutaraldehyde and analyzed by means of nuclear magnetic resonance relaxometry. In previous optical studies, these gels have shown promising dosimetric features in terms of photon sensitivity and low diffusion of ferric ions produced after irradiation.
In this work, we used a portable nuclear magnetic resonance relaxometer to measure the relaxation times (which are important for dosimetric applications) of these gel materials. For this purpose, we performed a study for optimizing the acquisition parameters with a nuclear magnetic resonance relaxometer. Gel samples were exposed to clinical 6 MV photons in the dose range between 0 and 20 Gy. Nuclear magnetic resonance relaxometry measurements were performed and the sensitivity to photon beams was measured for various values of the Fe²⁺ ion concentration. The analyses pointed out that the MR signal increases as the Fe²⁺ content increases  and the increase is  about 75 %  when the concentration of  Fe²⁺  ions is increased from 0.5 mM to 2.5 mM. Furthermore, the sensitivity improvement achieved with increasing the Fe²⁺ concentration is about 60 %. This paper shows that the portable nuclear magnetic resonance relaxometer used for analysis of porous materials can be used for characterization of these dosimetric gels and this study can be considered as the first step for the characterization of these dosimeters which in future could be used for 3-D dose mapping in clinical applications.

Key words: dosimetry, gel, nuclear magnetic resonance, polyvinyl alcohol, glutaraldehyde, radiotherapy

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