Perirectal spacers in radiotherapy for prostate cancer - a systematic review and meta-analysis

Perirectal spacers reduce the radiotherapy (RT) dose delivered to the rectum, but their impact on treatment toxicity remains debated. We conducted a systematic review and meta-analysis to synthesise emerging data (PROSPERO: CRD42024506380).

MEDLINE, Embase, Scopus, and Google Scholar were searched through 2024/08/18 for prospective randomised (RCT) and non-randomised trials evaluating the clinical outcomes of perirectal spacing in prostate cancer (PCa) patients. Random effects generalised linear mixed models were used to pool odds ratios (OR) for rectal adverse events (AEs) from RCTs. Non-randomised trials were summarised qualitatively. The risk of bias was assessed using the RoB2 and ROBINS-I tools.

Three RCTs (n = 645) were identified. The rates of grade ≥ 2 (G ≥ 2) rectal AEs in control groups were low, ranging 4.2-13.8% for early AEs and 0-1.4% for late AEs. Perirectal spacers were associated with decreased incidence of early G ≥ 2 rectal AEs (OR: 0.43; 95% CI: 0.19-0.96), but not of late G ≥ 2 rectal AEs (OR: 0.26; 95% CI: 0.02-2.91). Assuming a comparator risk of 7.1% and 1%, this corresponded to a number needed to treat of 26 patients to avoid one early AE, and 135 pa- tients to avoid one late G ≥ 2 AE, respectively. Randomised clinical trial were at moderate risk of bias due to concerns regarding the concealment of allocation.

There is evidence that perirectal spacers result in a small decrease in acute rectal toxicity. However, modern RT for clinically localised PCa is generally well-tolerated, and severe AEs are rare. Greater scrutiny of the risks and benefits associated with perirectal spacers is necessary.