MR-guided Single-fraction SBRT for Nodal Oligorecurrent Prostate Cancer (PINPOINT)

Improved MR-Guided Single-fraction Stereotactic Sblative Radiotherapy in Pelvic and Abdominal Nodal Oliorecurrent Prostate Cancer

This single-arm phase 2 trial investigates whether a single high-dose radiotherapy treatment can safely treat men whose prostate cancer has come back in a small number of lymph nodes in the pelvis or abdomen after curative treatment. Participants receive one fraction of 24 Gy delivered with MR-guided stereotactic body radiotherapy (SBRT), which uses MRI to visualise the tumour and surrounding organs during treatment. The main goal is to assess safety (severe side effects). The trial also evaluates local tumour control, longer-term side effects, time until hormone (androgen deprivation) therapy is needed, survival, and quality of life. The trial aims to enrol 48 patients.

PINPOINT is a prospective, investigator-initiated, single-centre, single-arm phase 2 trial of single-fraction MR-guided SBRT in patients with nodal oligorecurrent prostate cancer. Eligible men have PSMA-PET/CT-verified nodal relapse in the pelvis or abdomen following curatively intended local treatment.

All patients are simulated with MRI in treatment position and treated with 24 Gy in 1 fraction to the gross tumour volume (GTV) using inverse-planned step-and-shoot IMRT on an MR-linac. No CTV margin is added (CTV = GTV); PTV margins account for motion and set-up uncertainty. Normal-tissue constraints are prioritised over target coverage.

The primary endpoint is cumulative CTCAE v5 grade ≥4 treatment-related toxicity within 6 months. Sample size follows a Simon two-stage design (H0: grade 4-5 TRAE rate 15%; H1: 4%; one-sided α = 5%, power 80%), with an interim analysis after 6-month follow-up of the first 16 patients and a total of 48 patients. Follow-up continues for 5 years. Toxicity (CTCAE v5), quality of life (EQ-5D-5L, EORTC QLQ-C30) and patient-reported outcomes (PRO-CTCAE) are collected at baseline and through follow-up; PSA and PSMA-PET/CT (on rising PSA) follow standard of care.

Inclusion Criteria:

• Age ≥ 18 years
• Signed informed consent
• Histologically proven initial diagnosis of adenocarcinoma of the prostate
• ECOG performance status 0-2
• Biochemical recurrence after curatively intended local treatment (radical prostatectomy and/or radiotherapy), with PSMA-PET/CT-verified nodal relapse in the pelvis or abdomen
• Any additional sites of disease beyond the protocol-specified target lymph nodes must be considered suitable for ablative treatment
• Life expectancy > 6 months
• Lymph node size ≤ 2 cm

Exclusion Criteria:

• Medical contraindications to MRI
• Inability to tolerate the physical set-up required for SABR
• Overlap between prior radiation fields and the current target area leading to high risk of clinically significant normal-tissue injury
• Contraindications to pelvic radiotherapy (chronic pelvic inflammatory bowel disease)
• Uncontrolled intercurrent illness