Management of isolated local failures following stereotactic body radiation therapy for low to intermediate risk prostate cancer.

Abstract

66 Background: SBRT is a safe and effective treatment option for patients with low to intermediate risk prostate cancer (PCa). SBRT delivers high biologically effective doses resulting in very low PSA nadirs. Strategies to diagnose and confirm salvageable isolated local failures (ILF) are needed. This study aims to examine the incidence and approach to management of ILF after SBRT in a large single institution cohort. Methods: All patients with low or intermediate risk PCa treated with SBRT at our institution were eligible for this study. Treatment was delivered using the robotic SBRT with doses of 35-36.25 Gy in five fractions. ILF were diagnosed using mpMRI and/or biopsy prompted by PSA rise after achieving long-term nadir. Choice of salvage therapy and post-salvage PSA were ascertained on follow up. Results: Between December, 2008 to August, 2018, 998 men with low to intermediate risk prostate cancer were eligible for analysis. Twenty patients (low risk, n = 4; intermediate risk, n = 16) were found to have ILF on either MRI (n = 15) and/or biopsy (n = 17). Three patients with MRI-identified ILF elected active surveillance in lieu of biopsy. Median pre-treatment PSA was 7.5 ng/ml. Median time to diagnosis of ILF was 72 months (37-96 months) with median PSA at the time of ILF of 2.3 ng/ml (1.1-10 ng/ml). Median PSA doubling time was 17 months (5-22 months). Thirteen patients with biopsy proven ILF proceeded with salvage therapy (cryotherapy n = 12, HIFU n = 1). Of 12 patients who underwent cryotherapy, 8 had a post-treatment PSA of < 0.1ng/ml, two patient’s results were unavailable, one patient had a PSA nadir of 0.7 ng/ml and one patient had yet to undergo post-salvage PSA test at the time of this report. Conclusions: The incidence of ILF is rare in our series. Diagnosis and management of ILF post-SBRT continues to evolve in the era of successful salvage therapy. Our report suggests an important role for early utilization of MRI and confirmatory biopsy at relatively low PSA levels and long PSA doubling time. Additionally, undetectable PSA post-salvage therapy supports early treatment after identifying ILF. Larger trials are needed for refinement of patient selection and most appropriate salvage modality.