PVA gel dosimeters for radiotherapy applications

Abstract

Gel dosimeters for three-dimensional mapping of radiotherapy doses were introduced at Yale University in the mid-1980’s. Soon after, research and development in this field also started in Italy. Early work was done at the Istituto Superiore di Sanità, and at the Universities of Pisa and Milan. Several institutes now collaborate on this topic with the goal of developing new formulations of hydrogel matrices with improved characteristics of stability, sensitivity and spatial resolution compared to those of earlier Fricke-gel and polymer-gel systems. Contrary to earlier gels based on natural gelling agents, such as porcine skin gelatin and/or agarose, which suffer from limited batch -to-batch reproducibility, we chose to develop formulations based on synthetic poly vinyl alcohol chemically cross-linked with glutaraldehyde. Several gel formulations and production procedures were investigated and are illustrated. The properties of these gels were investigated through a variety of techniques, including curemetry to determine the influence of GTA concentration and temperature over gelation time as well as scanning optical absorption to determine the sensitivity of the detectors and the spatial stability of the response. Comparative results are presented for the formulations we investigated, including one that provides a lower detection limit in the order of 100 mGy and a linear respon se exceeding 30 Gy, which makes it suitable for the verification of complex 3D treatment plans. Compared to earlier version of the detectors, we also achieved a simplification of the manufacturing processes in order to facilitate the diffusion of this technology and its transition from the bench to the bedside