Safety and efficacy of rectal spacers in locally advanced prostate cancer

Biodegradable perirectal spacers reduce rectal irradiation and rectal toxicity during radiotherapy for prostate cancer (PCa). However, while their use is well-established in localised PCa, there is minimal data on locally advanced PCa. Objective: to determine safety and efficacy of rectal spacers in patients with cT3 disease. A prospective single-centre cohort study was conducted from 2022 to 2024. Inclusion: consecutive men with mpMRI-directed biopsy-proven cT1 to cT3 PCa, planned for external beam radiotherapy. All patients underwent spacer insertion with either SpaceOAR or Barrigel. Dosimetry ranged from 55 to 79.2 Gy over 20–41 fractions. 181 men were included. 119 (65.7%) had cT1c/cT2 disease, and 62 (34.3%) cT3a/b disease. Post-spacer rectal spacing did not differ significantly between the cT3 and cT1c/cT2 groups at midgland (1 cm ± 0.36 vs. 1.05 cm ± 0.37, p = 0.34) or apex (0.52 cm ± 0.27 vs. 0.59 ± 0.3, p = 0.12); a statistically significant difference was observed at the base (0.94 cm ± 0.32 vs. 0.82 ± 0.3, p = 0.01). Acute grade 1/2 GI toxicity occurred in 12.9% vs. 5.0% of patients (p = 0.06), and late toxicity in 4.3% vs. 1.1% (p = 0.22); neither difference reached statistical significance, and no grade ≥ 3 toxicity was reported in either group. Temporary urinary retention rates did not differ significantly between groups (17.7% vs. 13.4%, p = 0.44), and there was no refractory urinary retention, infective complications, or rectal mucosal injury in either group. Freedom from biochemical failure was 98.1% (51/52) in the cT3 group versus 100% (109/109) in the cT1c/cT2 group over a median follow-up of 8 months. In conclusion, these preliminary findings support the utility, technical feasibility and acceptable short-term safety of rectal spacer insertion in cT3 PCa.