Ultrasound-planned high-dose-rate prostate brachytherapy: Dose painting to the dominant intraprostatic lesion

Abstract Purpose To demonstrate the feasibility of using high-dose-rate (HDR) brachytherapy to deliver 125% of the prescription dose to the dominant intraprostatic lesion (DIL) as defined on multiparametric MRI while respecting critical organ dose constraints. Methods and Materials Twenty-six patients with biopsy-proven predominantly unilateral prostate cancer consented to a university ethics–approved Phase 2 study of selective dose escalation. Combined information from endorectal T2 MRI sequences, dynamic contrast enhancement, and apparent diffusion coefficient maps was used to contour the DIL and prostate. Images were fused to intraoperative transrectal ultrasound for transposition of the DIL. Treatment consisted of two fractions of 10 Gy HDR brachytherapy to the entire prostate with 12.5 Gy to the DIL, combined with 46 Gy in 23 fractions of external beam radiotherapy. Results All patients had intermediate- or high-risk disease; 25 of 26 had a visible DIL (mean volume, 2.9 cm 3 ; SD, 1.8). Mean percentage of prostate receiving prescription dose ( V 100 ) was 98.1% (SD, 1.2). Mean dose to 90% of the DIL was 13.4 Gy (SD, 1.0). The coverage of the DIL was excellent with a mean of 95.7% (SD, 5.0) receiving the planned escalation of 25%. Established dose constraints to rectum and urethra were respected in all cases; where DIL coverage was limited by proximity to urethra or rectum, a mean dose to 90% of the DIL of 12.3 Gy was achieved. Conclusions Modest dose escalation to the DIL (25–30%) using ultrasound-planned HDR brachytherapy is feasible for selected intermediate- and high-risk patients while respecting critical organ constraints and is achievable within the practice setting of a community cancer center.