PSOR2 Presentation Time: 11:35 AM: Effect of SpaceOAR on Patient-Reported Rectal Bleeding Following External Beam Radiation Therapy and Cs-131 Prostate Brachytherapy Boost

Abstract

<h3>Purpose</h3> To evaluate long-term patient reported rectal bleeding in patients with prostate cancer treated at our institution with and without SpaceOAR following external beam radiation therapy and Cesium-131 (131Cs) prostate LDR brachytherapy boost. <h3>Materials and Methods</h3> We started routinely offering SpaceOAR to patients treated with external beam radiation therapy and 131Cs prostate LDR brachytherapy boost from 2016 with goal of potentially reducing rectal toxicity, including late rectal bleeding. We analyzed patients treated with and without SpaceOAR with at least 6 months of follow-up, with treatment from January 2007 to February 2021. Patients were asked to fill out Expanded Prostate Cancer Index Composite (EPIC) QOL questionnaire pre-treatment and at each scheduled follow-up appointment. The EPIC questionnaire included the following categories related to rectal bleeding and bother from rectal bleeding. Rectal bleeding occurring more than "rarely" was deemed clinically significant and severe rectal bleeding was defined as occurring "usually" or "always". Clinically significant bother from rectal bleeding was defined as considering bleeding to be more than a "very small problem." Severe bother from rectal bleeding was defined as being a "moderate" or "big" problem. Univariate Cox regression was performed to assess for impact of SpaceOAR on incidence of clinically significant rectal bleeding, with censorship at maximum follow-up. <h3>Results</h3> 317 patients were included in the analysis, all of whom were treated with a combination of external beam radiation therapy and LDR brachytherapy boost. 172 patients (54.3%) had intermediate-risk prostate cancer, while 145 patients (45.7%) had high-risk disease. 157 patients (49.5%) received androgen deprivation therapy, while 160 patients (50.5%) did not. 87 patients (27.4%) underwent prostate LDR brachytherapy boost with SpaceOAR inserted in the operating room following completion of prostate seed implant, with remaining 230 patients (72.5%) treated without SpaceOAR. Median follow-up for patients who received SpaceOAR was 18 months (IQR 12-30 months), whereas median follow-up for patients who did not receive SpaceOAR was 54 months (IQR 36-72 months). Incidence of acute clinically significant rectal bleeding, occurring before 6 months, was 3.9% in the cohort treated without SpaceOAR and 3.4% in the cohort treated with SpaceOAR. Incidence of late clinically significant rectal bleeding was 19.6% without SpaceOAR and 0% with SpaceOAR. For patients who developed late clinically significant rectal bleeding, median time to development was 18 months (IQR 9-24 months). Prevalence of late clinically significant rectal bleeding at last follow-up was 3.5% without SpaceOAR. Incidence and prevalence of late severe rectal bleeding without SpaceOAR was 4.7% and 1.3%, respectively. Incidence of late clinically significant bother from rectal bleeding was 20% without SpaceOAR and 0% with SpaceOAR. Prevalence of late clinically significant bother from rectal bleeding at last follow-up was 4.3% without SpaceOAR. Incidence and prevalence of late severe bother from rectal bleeding without SpaceOAR was 10.9% and 2.2%, respectively. On univariate analysis, SpaceOAR utilization was significantly associated with reduction in incidence of clinically significant rectal bleeding (p=0.035, hazard ratio 0.033; 95% confidence interval 0.001-0.784). <h3>Conclusions</h3> Overall prevalence of late rectal bleeding following 131Cs LDR prostate brachytherapy at last follow-up was less than 5%. SpaceOAR was associated with lower incidence of clinically significant rectal bleeding occurring at 6 months post-treatment or later as assessed by the EPIC questionnaire. Given the lower median follow-up in the SpaceOAR group, additional follow-up is warranted to determine whether this reduction is maintained long-term.