Robust Optimization for Gynecological High-Dose Rate Interstitial BrachytherapyUsing Post-Hoc Uniformity Correction

Abstract

Graphical optimization (GO) is commonly used during forward planning high-dose rate (HDR) interstitial brachytherapy (IB) to conform prescription dose to high-risk clinical target volume (HRCTV) while limiting organs-at-risk (OAR) doses. However, this typically Results in variations in dwell times between adjacent dwell positions even within an interstitial catheter (Figure 1a). When using IB for locally advanced/recurrent gynecological cancers, a common fractionation approach involves 5 fractions delivered twice daily over 3 days. During this time, day-to-day variations in internal normal tissue anatomy (bowel/bladder filling) can occur. Connecting and disconnecting transfer tubes for each treatment may result in longitudinal movement of individual catheters. Above factors could impact actual dose delivered. To mitigate the impact of these variations, we seek to explore the impact of a post-hoc uniformity correction (PHUC) on the GO plan and report an initial clinical experience with using this robust optimized (RO) approach.