106 Background: To demonstrate feasibility of using high dose rate (HDR) brachytherapy to deliver 25% higher than prescription dose to the dominant intra-prostatic lesion (DIL) as defined on multi-parametric MRI for intermediate and high risk prostate cancer. Methods: Twenty six patients with predominantly unilateral disease consented to a University Ethics-approved phase II study of selective dose escalation. HDR brachytherapy was performed in weeks 1 and 3 of treatment, each delivering one fraction of 10 Gy to the whole prostate. External beam consisted of 46Gy/23 fractions starting 3 days after the first HDR fraction.T2 FSE images were obtained using 1.5T endorectal MRI in transverse, sagittal and coronal planes followed by Dynamic Contrast Enhancement after injection of gadolinium. Apparent Diffusion Coefficient maps were calculated. The DIL was contoured on the MRI and, following image registration, transposed to the preoperative TRUS performed in the treatment position. Intra-operative TRUS with source-delivery catheters in place was fused to the pre-op TRUS with the transposed DIL. The DIL was included in dose optimization criteria. Results: Twenty five of 26 patients had a visible DIL. Mean prostate percentage receiving the prescription dose (V100) was 98.2% (SD:1.1). Mean dose to 90% of the DIL (D90) was 13.2 Gy (SD: 1.7). DIL mean volume was 2.9 cc (SD:1.8) representing 9.5% (SD: 7.6) of the prostate volume. Coverage of the DIL was excellent with a median of 97% receiving the planned escalation of 25%. Established dose constraints to rectum and urethra were respected in all cases. The factor that limited DIL coverage was proximity to organs at risk. Peri-urethral location of the DIL limited coverage in five cases and two had a posterior DIL such that dose to the rectum limited escalation. However, these seven cases still achieved a mean DIL D90 of 12.2 Gy. Conclusions: Dose manipulation using US-planned HDR brachytherapy is readily achievable within the practice setting of a community cancer center. Dose escalation to the DIL to a mean of 132% of the prescribed dose for selected intermediate and high risk prostate cancer patients is feasible while respecting critical organ constraints. Further escalation is planned. Clinical trial information: NCT01605097.
A Dose-Escalation Study for High-Dose-Rate Brachytherapy Boost in Intermediate- and High-Risk Prostate Cancer Patients
