Room: Exhibit Hall | Forum 2
Purpose: Conventional treatment planning for prostate high-dose-rate brachytherapy (HDR-B) involves covering the prostate with the prescribed dose while minimizing hot spots. However, boosting the dose to the dominant intraprostatic lesion (DIL) may increase tumor control probability (TCP). We previously showed the feasibility of deformable registration between multiparametric MRI (mp-MRI) and transrectal ultrasound (TRUS) which could enable localization of the DIL during needle placement. The purpose of this study is to determine the extent to which the DIL could be boosted while maintaining organ-at-risk (OAR) sparing and prostate coverage.
Methods: Sixteen previously treated HDR-b patients were selected. All DILs were contoured on the mp-MRI and transferred to the treatment planning system through deformable MRI-CT registration. Three plans were analyzed for each patient: 1) The original (Orig) which had been optimized for prostate coverage and hot spot reduction, 2) New plan (Opt) using original needle placement but reoptimized, 3) New plan (Virt) in which one or two virtual needles were added in the DIL and reoptimized. New plans were optimized for DIL V150 coverage while sparing OAR.
Results: Mean DIL D90, V150 and V200 of 16 patients were significantly higher for Opt and Virt plans compared to Orig plans (p<0.01). Mean Urethra V125 of Opt and Virt plans was slightly higher than Orig plans. Mean V75 to rectum and bladder were not significantly different (p>0.30). The limiting factor for maximizing dose to the DIL was minimizing Urethra D10. Balancing Urethra D10 and DIL V150 resulted in a variable effect on prostate D90 across cases.
Conclusion: Use of mp-MRI image guidance to boost DIL in HDR-B planning could result in increased DIL V150 while meeting OAR constraints. Use of mp-MRI to place needles within DIL during TRUS imaging could significantly improve achievable boost dose level and coverage for DILs, and potentially increase TCP.
Not Applicable / None Entered.