Prospective, Randomized Controlled Pivotal Trial of Biodegradable Balloon Rectal Spacer for Prostate Radiation Therapy

Abstract

Purpose/ObjectivesRectal spacers have been shown to reduce rectal side effects in patients receiving prostate radiation. However, concerns remain regarding precise and reproducible gel injection. We evaluated efficacy and safety of a novel rectoprostatic spacer balloon which allows potential for controlled, adaptable deployment. This study tested co-primary hypotheses: 1) Balloon spacer would result in ≥ 25% reduction of rectal V70 in > 75% of subjects, and 2) Implantation procedure-related and rectal ≥ Grade 1 adverse events within 6 months (duration ≥ 2 days, CTCAE 4.0) would be non-inferior in balloon vs control subjects. Materials/Methods222 subjects were enrolled at 16 centers. All patients had T1-T3 prostate cancer without MRI evidence of posterior extraprostatic invasion. Randomization was 2:1 (balloon: control) and subject-blinded. Patients underwent transperineal TRUS-guided fiducial placement +/- balloon, followed by IMRT (81 Gy in 1.8 Gy fractions or biologically equivalent hypofractionated dose). For efficacy comparisons, plans were generated by a central core lab on pre- and post-implant CT scans. ResultsThe primary efficacy endpoint was met, with 97.9% of balloon subjects (139/142) having rectal V70 reduction >25% (p<0.001). Mean V70 was 7.0 % pre- vs 1.1% post- implant. The primary safety endpoint was met with balloon subjects experiencing fewer ≥ Grade 1 events, 18% vs 23% (p < 0.001 for non-inferiority). On pre-defined secondary endpoint of ≥ Grade 2 events, rates trended lower in balloon subjects (4.3% vs 6.5%, p=0.527). Mean perirectal spacing was 19 ±3.7mm and maintained through radiation treatment (18 ±3.9mm). Balloon resorption was observed on 6-month CT in 98.5% (133/135) of subjects. The EPIC QOL instrument was collected throughout study, and did not differ statistically between the study arms. ConclusionsBiodegradable rectal spacer balloon was effective in significantly reducing dose to rectum, and associated with decreased cumulative rectal plus implantation-related adverse events. Balloon resorption was consistently observed by 6 months.