Salvage External Beam Radiotherapy After HIFU Failure in Localized Prostate Cancer: A Single Institution Experience

Abstract

<h3>Purpose/Objective(s)</h3> Standard treatment options for localized prostate cancer include active surveillance, radical prostatectomy, or local radiotherapy. While the use of high-intensity focused ultrasound (HIFU) as a primary treatment remains investigational, it is sometimes offered to select patients. At the time of HIFU failure, there is a lack of data in salvage treatment approach. Available data includes only small retrospective series with short-term follow-up. We therefore sought to evaluate our institutional experience in a cohort of patients treated with salvage radiation therapy (SRT) after primary HIFU failure. <h3>Materials/Methods</h3> We conducted a retrospective analysis of patients who had local failure after HIFU. This cohort of patients received salvage external beam radiation therapy (EBRT) delivered via intensity modulated radiotherapy (IMRT). Our primary endpoint was biochemical failure-free survival (bFFS) based on the 'Phoenix' definition of PSA nadir + 2 ng/mL. Secondary endpoints included metastasis-free survival (MFS) and overall survival (OS). Kaplan-Meier analysis was performed examining bFFS, MFS and OS. Genitourinary and erectile dysfunction adverse events were analyzed. <h3>Results</h3> From 2010 to 2018, 12 patients had local relapse post primary HIFU and received salvage EBRT with or without androgen-deprivation therapy, 75% and 25% respectively. The mean initial PSA prior to salvage EBRT was 8.2ug/L (2.9-14.4ug/L). The median time from HIFU to salvage EBRT was 13.5 months (6-42 months). EBRT was delivered as either conventional (76-78 Gy in 38-39 fractions, n = 11) or hypofractionation (66 Gy in 22 fractions, n = 1). Mean PSA nadir post RT was 1.2ug/L (0.1-2.6 ug/L). Acute International Prostate Symptom Score (IPSS) as well as International Index of Erectile Dysfunction (IIEF) scores were similar to baseline (<i>P</i> = 0.5 and 0.1, respectively). Late toxicities were comparable to those reported in men receiving EBRT as their primary treatment for localized prostate cancer. At a median follow-up of 46 months, only one patient had biochemical recurrence and radiological progression. The 5-year bFFS and MFS were both 83.3%. There were no deaths at the time of this analysis (OS = 100%). <h3>Conclusion</h3> To our knowledge this is one of the largest series reporting on modern SRT post HIFU failure. Our analysis shows that salvage EBRT is feasible, effective and carries no additional acute and delayed toxicity.