A Prospective Study of MR-Guided Focal Salvage High Dose-Rate Brachytherapy for Radiorecurrent Prostate Cancer: Updated Results of 30 Patients

Abstract

<h3>Purpose/Objective(s)</h3> Salvage therapies for localized radiorecurrent prostate cancer often carry significant short- and long-term morbidity. Focal salvage high dose rate (HDR) brachytherapy is an appealing treatment technique which delivers an ablative dose of radiotherapy to the portion of the prostate containing recurrent disease; however, limited prospective data is available. We sought to explore the toxicities, health related quality of life and efficacy of focal salvage HDR brachytherapy after previous definitive radiotherapy. <h3>Materials/Methods</h3> Patients with locally recurrent prostate cancer after previous external beam radiotherapy (EBRT) and/or brachytherapy were enrolled on a prospective clinical trial. Patients received MRI-guided, ultrasound-based focal HDR brachytherapy delivered over two fractions of 13.5 Gy delivered 1-2 weeks apart. Adjuvant androgen deprivation therapy (ADT) was not used. Toxicity was measured using CTCAE v4. Posttreatment response was evaluated using MRI 1-2 years after salvage. Biochemical failure was defined as PSA nadir + 2ng/mL. <h3>Results</h3> Thirty patients were treated between November 2012 and September 2019. Median follow-up was 35 months (range: 13 – 92 months). Fifteen patients were initially treated with EBRT, 3 with low dose rate (LDR) brachytherapy monotherapy, 1 with EBRT and LDR brachytherapy boost, 2 with EBRT and HDR brachytherapy boost, and 9 with HDR brachytherapy as monotherapy (all 19 Gy in a single fraction). Median clinical target volume (CTV) at time of salvage was 5.22 mL (range: 2.18 – 15.71 mL), corresponding to a median of 20.0% of the prostate volume (range: 8.8% – 39.2%). Median PSA at salvage was 4.46 ng/mL (range: 0.99 – 11.63 ng/mL). The median CTV V100 was 96.5% (range: 90.5% – 99.5%), and median CTV D90 was 15.1 Gy per fraction (range: 13.6 – 18.1 Gy). Seventeen patients experienced subsequent biochemical failure, and 9 have received ADT and/or further local salvage. No patients have died from prostate cancer. Median time to biochemical failure was 41.5 months, and median time to ADT/salvage therapy was 70.6 months. The three-year biochemical failure-free event rate was 61.8% (95% CI 44.0 – 86.6%), and three-year ADT/salvage therapy-free event rate was 86.0% (95% CI 74.1 – 99.8%). No acute grade ≥ 3 GU/GI toxicity was observed. One late grade 3 GU toxicity event occurred, cystitis at 42 months post treatment, which did not persist on follow-up. No late grade ≥ 3 GI toxicity was seen. Of the 28 patients who had a post-treatment MRI, 26 had evidence of a local treatment response. <h3>Conclusion</h3> In our updated results, we found focal salvage HDR brachytherapy is well tolerated with a favorable side effect profile and 3-year biochemical control rates in line with other salvage therapies for radiorecurrent prostate cancer. While early MRI response at the treated site is common, this does not preclude subsequent biochemical failure.