169 Yb-based high dose rate intensity modulated brachytherapy for focal treatment of prostate cancer

This study compares conventional Ir-based high dose rate brachytherapy (HDR-BT) with Yb-based HDR intensity modulated brachytherapy (IMBT) for focal prostate cancer treatment. Additionally, the study explores the potential to generate less invasive treatment plans with IMBT by reducing the number of catheters needed to achieve acceptable outcomes. A retrospective dosimetric study of ten prostate cancer patients initially treated with conventional Ir-based HDR-BT and 5-14 catheters was employed. RapidBrachyMCTPS, a Monte Carlo-based treatment planning system was used to calculate and optimize dose distributions. For Yb-based HDR IMBT, a custom Yb source combined with 0.8 mm thick platinum shields placed inside 6F catheters was used. Furthermore, dose distributions were investigated when iteratively removing catheters for less invasive treatments. With IMBT, the urethra D and D decreased on average by 15.89 and 15.65 percentage points (pp) and the rectum V and D by 1.53 and 11.54 pp, respectively, compared to the conventional clinical plans. Similar trends were observed when the number of catheters decreased. On average, there was an observed increase in PTV V from 2.84 pp with IMBT when utilizing all catheters to 8.83 pp when four catheters were removed. PTV V increased from 0.42 to 2.96 pp on average. Hotspots in the body were however lower with IMBT compared to conventional clinical plans. Yb-based HDR IMBT for focal treatment of prostate cancer has the potential to successfully deliver clinically acceptable, less invasive treatment with reduced dose to organs at risk.