This prospective single-arm phase II study evaluates the safety, feasibility, quality-of-life effects, PSA kinetics, imaging response, and clinical outcomes of definitive ultra-high dose single-fraction external beam radiation therapy in patients with biopsy-proven NCCN intermediate-risk localized adenocarcinoma of the prostate.
All eligible patients receive image-guided volumetric modulated arc radiotherapy with urethral sparing and organ-motion mitigation. Treatment consists of 24 Gy in one fraction to the whole prostate gland and proximal seminal vesicles. Patients with NCCN unfavorable intermediate-risk disease and an imaging-defined dominant intraprostatic lesion may receive a PSMA PET/CT-guided simultaneous integrated boost to the dominant intraprostatic lesion in sequential dose-escalation cohorts, up to 30 Gy, while maintaining protocol-defined organ-at-risk constraints.
A rectal balloon with air filling is used for prostate target immobilization and anatomical reproducibility, and a urethral catheter loaded with beacon transponders is used to identify the urethra, support urethral sparing, and enable online target tracking. Toxicity is assessed using CTCAE v4.0, and patient-reported outcomes are assessed using EPIC-26, IPSS, and IIEF questionnaires. PSA is measured at protocol-defined follow-up visits. Multiparametric MRI is performed at baseline and at 12 and 24 months after treatment. Participants are followed for a minimum of 5 years.
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Single group
IGRT-VMAT / SDRT 24 Gy in 1 fraction
RadiationPSMA PET/CT-guided dominant intraprostatic lesion simultaneous integrated boost
Rectal balloon with air filling
DeviceA rectal balloon with air filling will be used for prostate target immobilization and anatomical reproducibility.
Urethral catheter loaded with beacon transponders
DeviceA urethral catheter loaded with beacon transponders will be used to ensure set-up reproducibility and online target tracking.
PSMA PET/CT for DIL definition and/or staging where protocol-required
Diagnostic testPSMA PET/CT for DIL definition
Planning MRI for organ at risk and target definition
Diagnostic testPlanning MRI for organ at risk and target definition. mpMRI will also be used to aid DIL definition in conjunction with PSMA-PET/CT
Incidence of acute grade ≥2 GU and/or GI toxicity
Proportion of treated participants with physician-assessed CTCAE v4.0 grade ≥2 genitourinary and/or gastrointestinal toxicity occurring from protocol treatment through 90 days after treatment.
Late GU and GI toxicity
Incidence and grade of physician-assessed CTCAE v4.0 GU and GI toxicity occurring more than 90 days after treatment.
Dose-limiting acute GU/GI toxicity
Proportion of participants with CTCAE v4.0 grade ≥3 acute GU or GI toxicity within 90 days after treatment, used for DIL-SIB cohort-escalation safety monitoring.
Quality-of-life change over time
Change from baseline in EPIC-26 scores. The EPIC-26 (Expanded Prostate Cancer Index Composite score) questionnaire ranges between 0 and 100, with higher values indicating better quality of life.
Clinically meaningful EPIC-26 urinary decline
Proportion of participants with EPIC-26 urinary-domain decline ≥6 points from baseline. The EPIC-26 (Expanded Prostate Cancer Index Composite score) questionnaire ranges between 0 and 100, with higher values indicating better quality of life.
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