Multicenter study on mechanical accuracy of short dwell time and source transit for HDR Ir-192 brachytherapy...

To evaluate the accuracy of the effective transit and dwell times for high-dose-rate (HDR) brachytherapy machines across multiple institutions. The aim was to establish reference levels for quality assurance (QA) in MicroSelectron and Flexitron afterloaders.

The effective transit time of the amount of charge from the moving source divided by the current value and the short dwell times were measured using institution-owned well-type ionization chambers for 11 treatment machines from 10 institutions, including MicroSelectron and Flexitron afterloaders. Measurements were performed under standardized conditions to minimize variability, including controlled distances from walls and floors to reduce scattered radiation. The proportionality constants and effective transit times were calculated and the dwell times were measured for settings ranging from 0.1 to 30 s. For each afterloader, effective transit time and dwell time accuracy were measured five times, and the averages were used for analysis.

MicroSelectron afterloaders exhibited mean effective transit times of 0.90-1.05 s, whereas Flexitron afterloaders showed shorter times of 0.54-0.62 s. For the dwell time accuracy, MicroSelectron afterloaders exhibited a mean error of -0.048 to 0.104 s, with larger variability across institutions. In contrast, Flexitron afterloaders showed a mean error consistently below ±0.01 s, even at shorter dwell times. The variability in dwell time was notably significant higher for MicroSelectron than for Flexitron afterloaders (p ≤ 0.002).

This study demonstrates clear performance differences between MicroSelectron and Flexitron afterloaders in HDR brachytherapy and provides reference levels that support device-specific QA protocols to improve treatment precision and ensure consistent outcomes across institutions.