Purpose

Prostate brachytherapy is routinely performed with trans-rectal ultrasound (TRUS)- or computed tomography (CT)-based planning that cannot delineate dominant intra-prostatic lesions (DILs). In contrast, magnetic resonance imaging (MRI)-based planning allows for more accurate DIL delineation and dose escalation. This study assessed the maximum achievable dose escalation to DILs.

Material and methods

We retrospectively identified 24 patients treated with high-dose-rate (HDR) prostate brachytherapy boost (15 Gy in 1 fraction). All patients had a pre-treatment prostate MRI with 1-3 DILs. MRIs were used to delineate DILs and were co-registered to TRUS intra-procedure. Treatment plans were experimentally re-optimized to escalate DIL dose. Dosimetric indices from the original and re-optimized plans were compared using two-tailed paired t-test. Re-optimized plans were deemed acceptable if they achieved all of the following criteria: prostate D90 > 100%, prostate V100 > 90%, urethra D10 < 118%, rectum V80 < 0.5 cc, bladder D1cc < 75%, or if they did not exceed organs at risk (OARs) doses of the original plan.

Results

The mean DIL D90 was significantly increased from 134% of the prescription dose on the original plans to 154% on the re-optimized plans. The mean urethra D10 and mean bladder D1cc were significantly reduced from 123% to 117% and from 72% to 65%, respectively. Prostate D90 was reduced from 106% to 102%, and prostate V100 was reduced from 93% to 91%.

Conclusions

We re-optimized HDR brachytherapy plans to escalate DILs dose to a mean D90 of > 150% while maintaining favorable prostate coverage and OARs doses. We propose DIL D90 dose of > 150% (22.5 Gy) as an achievable goal.