Preliminary evaluation of ProSpare®, a rectal obturator for prostate bed radiotherapy within the randomised multicentre POPS trial (NCT02978014)
11 affiliations
- 1The Institute of Cancer Research, London, United Kingdom
- 2Royal Marsden Hospital, London, United Kingdom
- 3Ipswich Hospital, Ipswich, United Kingdom
- 4Royal Surrey NHS Foundation Trust, Guildford, United Kingdom
- 5University College Hospital, London, United Kingdom
- 6Musgrove Park Hospital, Taunton, United Kingdom
- 7Mount Vernon Cancer Centre, Northwood, United Kingdom
- 8Royal Free London NHS Foundation Trust, London, United Kingdom
- 9Norfolk and Norwich University Hospitals NHS Foundation Trust, Norwich, United Kingdom
- 10Addenbrooke’s Hospital, Cambridge, United Kingdom
- 11Ipswich Hospital NHS Trust, Ipswich, United Kingdom
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.
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BibTeX
@article{stewart2026preliminary,
title = {{Preliminary evaluation of ProSpare®, a rectal obturator for prostate bed radiotherapy within the randomised multicentre POPS trial (NCT02978014)}},
author = {Sarah Stewart and Karen Thomas and Jenni Parmar and Alison Claire Tree and Chris Parker and Helen McNair and Sophie Alexander and Julia Henderson and James Talbot and Christopher Scrase and Chee Goh and Reena Davda and Emma Gray and Peter Hoskin and Sarah Needleman and Jenny Nobes and Kamalram Thippu Jayaprakash and Yvonne Rimmer and Ranachandran Venkitaraman and Anna Wilkins and Vincent Khoo and Julia Murray and David Paul Dearnaley},
journal = {Frontiers in Oncology},
year = {2026},
month = oct,
doi = {10.3389/fonc.2026.1758462},
url = {https://doi.org/10.3389/fonc.2026.1758462},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Preliminary evaluation of ProSpare®, a rectal obturator for prostate bed radiotherapy within the randomised multicentre POPS trial (NCT02978014)
AU - Sarah Stewart
AU - Karen Thomas
AU - Jenni Parmar
AU - Alison Claire Tree
AU - Chris Parker
AU - Helen McNair
AU - Sophie Alexander
AU - Julia Henderson
AU - James Talbot
AU - Christopher Scrase
AU - Chee Goh
AU - Reena Davda
AU - Emma Gray
AU - Peter Hoskin
AU - Sarah Needleman
AU - Jenny Nobes
AU - Kamalram Thippu Jayaprakash
AU - Yvonne Rimmer
AU - Ranachandran Venkitaraman
AU - Anna Wilkins
AU - Vincent Khoo
AU - Julia Murray
AU - David Paul Dearnaley
PY - 2026
DA - 2026/10/12
JO - Frontiers in Oncology
DO - 10.3389/fonc.2026.1758462
UR - https://doi.org/10.3389/fonc.2026.1758462
AB - 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.
SN - 2234-943X
ER -