Association between perirectal spacer use and complications following prostate radiation therapy: Results of a national real-world data analysis.

571 Background: By increasing distance between the rectum and prostate, perirectal spacers have been shown to reduce rectal doses during prostate radiotherapy and gastrointestinal toxicity in clinical trials. We aimed to assess rectal and urinary complications in a national sample of individuals receiving prostate radiotherapy with and without a rectal spacer. Methods: Within the Merative MarketScan Research Databases, we identified beneficiaries with prostate cancer receiving prostate radiotherapy from 2016 to 2022. Beneficiaries were classified based on whether they underwent rectal spacer placement before prostate radiotherapy. The primary outcome was the incidence of rectal and urinary toxicities within 12 months of treatment between beneficiaries with rectal spacer and those without. Multivariable Cox regression models assessed the association between urinary complications and rectal spacer use, controlling for age, Elixhauser Comorbidity Index, insurance type, androgen deprivation therapy use, and radiation type. Results: We identified 47,734 eligible beneficiaries in the study period, including 6,681 (14.0%) with evidence of pre-treatment rectal spacers and 41,053 (86.0%) without. One-year incidence of radiation proctitis (0.9% vs. 1.3%, p<0.01), rectal bleeding (3.5% vs. 6.6%. p<0.01), urinary tract infection (5.6% vs. 6.3%, p=0.03) and urinary incontinence (1.0% vs. 1.4%, p<0.01) were lower in beneficiaries with rectal spacers compared to those without. No significant difference was seen in the incidence of hematuria (2.5% vs 2.6%, p=0.9). Receipt of a rectal spacer was associated with a lower hazard of radiation proctitis ((hazard ratio (HR) 0.57, 95% CI: 0.47-0.70, p<0.01), rectal bleeding (HR 0.70, 95% CI: 0.61-0.82, p<0.01), urinary tract infections (HR 0.86, 95% CI: 0.78-0.96, p<0.01) and urinary incontinence (HR 0.71, 95% CI: 0.57-0.90, p<0.01), but not hematuria (HR 0.92, 95% CI: 0.81-1.04, p=0.2). Conclusions: In this national observational study of beneficiaries receiving prostate radiotherapy, the analysis suggests that rectal spacer use is associated with a lower incidence of rectal and select urinary complications. Future studies incorporating patient-reported outcomes are needed to provide a better understanding of the effectiveness of these interventions.