There is growing evidence for the use of biodegradable perirectal spacers to reduce rectal irradiation and gastrointestinal (GI) toxicity during radiotherapy for prostate cancer (PCa). However, while safety and efficacy have been well established in localised PCa, there is minimal data on locally advanced PCa. This study aims to evaluate both the safety and efficacy of rectal spacers in patients with T3 disease receiving external beam radiotherapy (EBRT).

From 2022 to 2024, we collected prospective single-centre data of consecutive patients with biopsy-proven T1 to T3 PCa who underwent perirectal spacer placement followed by EBRT. Patients received either SpaceOAR or Barrigel spacers, and underwent planning computed tomography (CT) scans prior to starting EBRT. Dosimetry ranged from 50—79.2Gy given over 20 fractions. Patient data, pre- and post-implantation rectal distances, radiation dosimetry, and toxicity outcomes were evaluated. Rectal spacing was used as a surrogate for dose reduction.

181 men were included, of which 17 (9.4%) had T1c disease, 102 (56.4%) T2 disease, and 62 (34.2%) T3a/b disease. Mean prostate volume was 41.6cc. Rectal spacing achieved was similar across the groups: in the T3 group compared to the T1c/T2 group, rectal spacing achieved was 0.94cm±0.32 vs 0.82±0.3 (p=0.01) at the base, 1cm±0.36 vs 1.05cm±0.37 (p=0.34) at the midgland, and 0.52cm±0.27 vs 0.59±0.3 (p=0.12) at the base. Despite the T3 group receiving a higher dose of radiation overall, toxicities were similar across the two groups, with 12.9% (8/62) reporting acute grade 1/2 GI toxicity and 4.3% (2/46) reporting late toxicity in the T3 group, compared to 5.1% (6/119, p=0.06) acute and 1.1% (1/90, p=0.22) late toxicities in the T1c/T2 group. No grade ≥3 toxicity was reported in the acute or late stage in both groups. As for safety profile, 14.5% (11/62) of T3 patients compared to 11.7% (14/119) of T1c/T2 patients developed temporary urinary retention requiring catheter insertion (p=0.44). There was no refractory urinary retention beyond 2 weeks, no infective complications, and no rectal mucosal injury in both groups. Additionally, while there have been some concerns regarding RT local failure with spacer usage in T3 disease, our study found otherwise. Between the T3 and T1c/T2 groups, freedom from biochemical failure was similar: 98.1% (51/52) compared to 100% (109/109, p=0.15) over a median follow-up period of 8 months (IQR 3-13 months).

Rectal spacer placement in patients with T3 disease demonstrates a similar complication rate compared to those with T1c or T2 disease. Additionally, despite receiving higher doses of radiation, patients with T3 disease experience similar rates of acute and late rectal toxicity as their T1c/T2 counterparts. Rectal spacers should be considered in suitable patients with locally advanced PCa for better tolerance of EBRT.