Ultra-Hypo Fractionated Prostate IGRT with HDR Brachytherapy Boost as Compared to a Moderate-Hypo Fractionated Approach: Patient Reported Outcomes (PRO's) of a Phase Two Study Interim Analysis

Abstract

<h3>Purpose/Objective(s)</h3> To report and compare PROs of an HDR brachytherapy (BB) combined to an ultra-hypo fractionated (UHF) prostate radiation therapy regimen as opposed to a moderate hypo fractionated (MHF). <h3>Materials/Methods</h3> This interim analysis of a prospective mono-centric phase 2 study includes 75 prostate cancer patients, mostly intermediate risk, recruited between July 2015 and September 2021. Using an image guided radiation therapy technique (IGRT), 25 Gy in 5 fractions plus 15 Gy HDR BB were delivered to the experimental arm (Exp). The control groups consisted of contemporary patients treated with IGRT and HDR BB (15 Gy) with 36 Gy in 12 fractions (Ctrl; n=119). IGRT treatment time is reported. Patient reported outcomes were collected using the International Prostate Symptom Score (IPSS) questionnaire at baseline and at each follow-up visits. A comparative linear mixed model analysis was performed on log transformed IPSS values. Expanded prostate cancer index composite-26 (EPIC-26) was also reported and compared between groups with a mixed model analysis. Biochemical relapse-free survival (BRFS) is reported. <h3>Results</h3> The 2 groups were similar with no statistical differences regarding: the median age (68 years), stage (T1C), Gleason scores (7), PSA (<10) and risk grouping (favorable intermediate). Median follow-up was 8 and 49 months respectively for Exp & Ctrl. The mixed model analysis showed that mean IPSS scores diverge with a significant difference in favor of Exp at 6, 12 and 24 months. Analysis of EPIC-26 data showed no differences throughout follow-up between Exp and Ctrl in all domains. To the patient's convenience, UHF median treatment was delivered in 7 days as compared to 17 days for MHF. Considering a short follow-up in the Exp group, its BRFS was 100% compared to 94.6 for Ctrl and these differences are not significative. <h3>Conclusion</h3> At the interim analysis, IPSS PROs for UHF treatment scheme with HDR BB seems to be significantly better tolerated at multiple FU time point compared to the control. However, there was no significant differences between groups reported with the EPIC-26. UHF treatment shorten treatment span by 10 days and given the short FU, seemingly provides similar BRFS. Therefore, we will pursue accrual to our phase 2 study.