Verification of the dose distribution calculated by the treatment planning system in high dose rate brachytherapy

Abstract

For HDR brachytherapy, there is still no clear optimum method used to measure dosimetric accuracy. For brachytherapy, there is a steep dose fall off with distance which can make dosimetric measurements more challenging when compared with external beam radiation therapy (EBRT). It is important that as HDR brachytherapy continues to develop that quality control measures develop also. The aim of this study is to verify the dose distribution for HDR brachytherapy using Gafchromic film. This was done by verifying the treatment dose for three brachytherapy applicators; the cylinder, fletcher and flap applicators. Each applicator was placed in a water phantom with calibrated Gafchromic film placed at known locations. The phantoms were scanned and planned on the brachytherapy treatment planning system (TPS), and the dose to the film noted. After irradiation the Gafchromic film was scanned and analysed. The results showed that the cylinder applicator had the largest percentage difference between the TPS dose and calculated dose with a difference of 11.93%. Smaller differences of 7.99% and 6.07% were seen for the fletcher and flap applicators respectively. However, uncertainties in these results were seen for each of the applicators and should be taken into account. It was observed that the Gafchromic film overestimated the dose for the three applicators, however provided steps were taken to reduce these uncertainties Gafchromic film does have the potential to be used as a QA tool to measure the dose distribution for HDR brachytherapy which this study set out to do.