Dose distribution verification in high-dose-rate brachytherapy using a highly sensitive normoxic N-vinylpyrrolidone polymer gel dosimeter.

Rapid technological advances in high-dose-rate brachytherapy have led to a requirement for greater accuracy in treatment planning system calculations and in the verification of dose distributions. In high-dose-rate brachytherapy, it is important to measure the dose distribution in the low-dose region at a position away from the source in addition to the high-dose range in the proximity of the source. The aim of this study was to investigate the accuracy of a treatment plan designed for prostate cancer in the low-dose range using a normoxic N-vinylpyrrolidone-based polymer gel (VIPET gel) dosimeter containing inorganic salt as a sensitizer (iVIPET). The dose response was evaluated on the basis of the transverse relaxation rate (R2) measured by magnetic resonance scanning. In the verification of the treatment plan, gamma analysis showed that the dose distributions obtained from the polymer gel dosimeter were in good agreement with those calculated by the treatment planning system. The gamma passing rate according to the 2%/2 mm criterion was 97.9%. The iVIPET gel dosimeter provided better accuracy for low doses than the normal VIPET gel dosimeter, demonstrating the potential to be a useful tool for quality assurance of the dose distribution delivered by high-dose-rate brachytherapy.

[Polymer Gel Dosimetry for the High-Dose-Rate Brachytherapy Using Ir-192 Source].

High-dose-rate (HDR) brachytherapy is performed with the remote after-loading system (RALS) to transport an Ir-192 source directly to inside or near the tumor. Quality assurance (QA) of equipment should be performed at sufficient frequency to ensuring safety and quality of HDR brachytherapy treatment. Polymer gel dosimeters have been attracting attention in recent years as a QA tools of HDR brachytherapy, because they can measure the three-dimensional steep dose gradients around HDR sources. In this paper, we introduce our preliminary results using VIPET polymer gel dosimeters for Ir-192 HDR brachytherapy dosimetry.