Preparation and Use of 131 I Magic Gel as a Dosimeter for Targeted Radionuclide Therapy

Abstract

Clinical interest in targeted radiotherapy is increasing, but accurate dosimetry studies are difficult to achieve. The aim of this study was to investigate the preparation and use of a "normoxic" polymer gel(with a tissue-equivalent density), known as MAGIC gel, and magnetic resonance imaging (MRI) for nonsealed source dosimetry. MAGIC gel samples were mixed with deionized water (MAGIC₉₅) or a solution of ¹³¹I (¹³¹I-MAGIC₉₅). By measuring the radioinduced variations of R₂ values (relaxivity) of irradiated gels, we analyzed the response of MAGIC₉₅ and MAGIC samples to external photon beam or ¹³¹I irradiation(¹³¹I-MAGIC₉₅). MRI showed that a homogeneous dose distribution from ¹³¹I can be achieved if the MAGIC gel, at a temperature of approximately 35°C, is mixed in ¹³¹I solution and the resulting mixture shaken gently for 30 minutes. It is important that the vials are completely filled, as residual air reduces polymerization and causes spontaneous polymerization stripes. Responses of MAGIC₉₅ or MAGIC gels to external photon beam irradiation are similar. The variations of R₂ values for ¹³¹I-MAGIC₉₅ gel depend on the absorbed dose and not on the duration of the irradiation being reproducible from one batch of gel to another. MAGIC gel responses to ¹³¹I or external beam irradiation (EBI) are different. Our preliminary results suggest that radiolabeled "normoxic" polymer can be easily and safely produced. Radiolabeled MAGIC gel may, therefore, be suitable for the creation of phantoms dedicated to nonsealed source dosimetry.