Work

Preliminary evaluation of ProSpare®, a rectal obturator for prostate bed radiotherapy within the randomised multicentre POPS trial (NCT02978014)

Year: 2026

Type: article

Abstract: Background and purpose The introduction of volumetric modulated arc therapy (VMAT) has enabled dosimetric improvements during prostate bed (PB) radiotherapy; however, the planning target volume (PTV) margins remain substantially greater than for prostate radiotherapy. New approaches are required to further optimise rectal dose and minimise target and organ motion. ProSpare ® , a self-inserted rectal obturator designed to facilitate daily image guidance, may enhance radiotherapy accuracy and reduce treatment-related morbidity. Materials and methods Patients scheduled to receive adjuvant or salvage PB radiotherapy after radical prostatectomy were randomised to either standard-of-care (SOC) PB-IMRT using centre-standard PTV margins and verification protocol (SOC) or PB-IMRT with daily ProSpare ® -guided radiotherapy using a reduced 5-mm posterior margin. Dose and fractionation schedules were selected by each centre according to protocol recommendations. The primary endpoint is patient-reported EPIC bowel function and bother at 2 years. Secondary endpoints include acute Radiation Therapy Oncology Group (RTOG) and CTCAE toxicity, patient-reported outcomes, device tolerability, and anorectal dosimetry. We report the results from the prespecified analysis of these secondary endpoints. Results Between 2017 and 2023, 162 patients were recruited; 158 began radiotherapy and were evaluable at 18 weeks. Acute toxicity data were available for 146 patients (SOC 76/81, ProSpare 70/77). Compared with SOC, ProSpare ® was associated with lower 18-week RTOG ≥grade 1 gastrointestinal (GI) and genitourinary (GU) toxicity (39% vs. 31% and 37% vs. 29%, respectively). The incidence of worst CTCAE grade 2 GI and GU toxicity was <6%. Of 51 responders, 50 found ProSpare ® tolerable and would recommend its use. Use of ProSpare ® resulted in consistently lower ano-rectal dose–volume parameters. Conclusion ProSpare ® -guided prostate bed radiotherapy (PBRT) resulted in lower acute RTOG bowel toxicity at all time points. Patient-reported tolerability was very favourable. Use of ProSpare ® improved rectal and anal canal dosimetry. Clinical Trial Registration ClinicalTrials.gov , identifier NCT02978014.

Source: Frontiers in Oncology

DOI: 10.3389/fonc.2026.1758462