Sci-Sat AM(2): Brachy - 01: A Quality Assurance Tool for High-Dose-Rate Brachytherapy

Abstract

The purpose of this work was to develop a quality assurance (QA) tool for high-dose-rate brachytherapy that would quickly and easily verify both source positioning (dwell positions) and durations (dwell times). We constructed a QA tool that combined radiochromic film to verify position with four photodiode detectors to verify dwell times. To characterise the temporal accuracy of the tool, a function generator powered four red light-emitting diodes that were optically coupled to the four photodiode detectors. Our QA tool was used to verify the dwell positions and times of a commercial brachytherapy afterloader. Measurements of dwell time were independently verified by a one-dimensional optical camera that acquired 1000 lines per second. The temporal accuracy of the QA Tool was found to be about 1 ms. For visual assessment, the source position could be located to within about 0.5 mm. Evaluating the accuracy and precision of an HDR brachytherapy afterloader, we found that the bias in dwell time can exceed 60 ms and the dwell time associated with the first dwell position had an unexpectedly large standard deviation of 30 ms. We found the source locations were much easier to locate on the film if a plastic catheter was used instead of a metal treatment tube. Scanning the films enabled the dwell positions to be determined to within about 0.2 mm. For pre-treatment QA, we found that this tool allowed verification of dwell positions and dwell times in about 6 minutes.