Improving Treatment Plan Quality Using Optimization Templates for Prostate High Dose Rate (HDR) Brachytherapy with Dominant Intraprostatic Lesion (DIL) Boost
Abstract
Purpose
Prostate High Dose-Rate (HDR) Brachytherapy with Dominant Intraprostatic Lesion (DIL) boost is well tolerated for high-risk patients. Ultrasound-guided prostate HDR is a time-sensitive procedure with treatment planning subject to variability, especially for small glands and glands with large DILs. We aim to benchmark and improve the quality, consistency, and efficiency of treatment planning by optimizing the inverse planning dose–objective template. We present optimization templates and their performance across a range of clinical cases.
Methods
Thirty-five plans were reviewed retrospectively, each receiving 15Gy to the prostate and 18Gy to the DIL. Two optimization templates (VEGO, Vitesse TPS, Varian) were evaluated: the current clinical template and a modified template incorporating a ring structure around the Prostate+2mm and DIL+4mm volumes. Plans were generated using both templates without manual intervention and benchmarked against clinically delivered plans using coverage, organ-at-risk (OAR), and conformality index (COIN) metrics.
Results
Prostate volumes ranged from 11cc to 55cc (median 25.3 cc). All plans met target coverage (PTV D90%≥95-115%; DIL D90%≥120%) requirements. The modified template demonstrated statistically significant improvement in conformity index (mean COIN 0.68, range 0.60-0.76) versus the default template (mean COIN 0.67, range 0.54-0.77, p = 0.03) and clinical plans (mean COIN 0.66, range 0.49-0.76, p = 0), with the largest improvements at lower prostate volumes. There was no significant increase in OAR doses between clinical plans and new template plans. The new template was as efficient as the original one in generating clinically acceptable plans that met all constraints without any manual changes (63%). A linear fit was created for COIN v prostate volume to provide a preliminary predictive model.
Conclusion
This template-based approach establishes a robust baseline for high-quality prostate HDR brachytherapy with DIL Boost. The inclusion of a ring structure in the optimization offers improved conformality while maintaining acceptable target coverage and OAR sparing.