KEY POINTS
- This prospective single-center cohort included 51 men receiving salvage or early-salvage radiotherapy at least six months after radical prostatectomy. Eligibility included biochemical recurrence, persistent/rising PSA, adverse pathology or PSMA-PET/MRI-detected locoregional recurrence; all patients were staged M0 on PSMA-PET before treatment.
- Treatment was delivered on a 1.5-T MR-Linac using daily Adapt-to-Shape replanning with a 5-mm CTV-to-PTV margin. Thirty-four patients received prostate-bed treatment alone and 17 also received pelvic nodal irradiation; prescriptions ranged from 52.5 Gy/20 fractions to 70 Gy/35 fractions.
- 24/51 patients (47%) received a PSMA-PET/MRI-guided simultaneous integrated boost to gross recurrence, adding 4.0–12.5 Gy above the prostate-bed prescription. OAR constraints were prioritized over boost coverage, including limiting urethral dose to 107% of the prostate-bed rather than boost prescription.
- Baseline-adjusted new or worsened grade ≥2 genitourinary toxicity remained low: 3.9% at 3 months, 2.0% at 6 months, 6.0% at 12 months and 10.0% at latest follow-up. Only one patient had grade 3 urinary toxicity, occurring on a background of pre-existing grade 2 incontinence.
- Gastrointestinal toxicity was particularly limited. New grade ≥2 gastrointestinal toxicity occurred in 1/51 patients (2.0%) at 3 months, with no grade ≥2 events at 6 or 12 months or latest follow-up. Any-grade gastrointestinal toxicity was 12% at 12 months.
- Boosting gross recurrence did not produce a detectable toxicity penalty. At 12 months, grade ≥2 toxicity occurred in 4.2% with SIB versus 14.8% without SIB (P=.35); no statistically significant difference in any-grade or grade ≥2 toxicity was found at any evaluated timepoint, although these subgroup analyses were exploratory and underpowered.
- After median follow-up of 20.8 months, biochemical progression occurred in 10/51 patients (20%), with 12-month biochemical progression-free survival of 84.3% (95% CI 74.8–94.9%). Among 31 men not receiving ADT, median PSA fell 95.2% at three months; all subsequent nodal or distant recurrences occurred outside the salvage radiation fields.
CLINICAL TAKEAWAY
Daily MR-guided adaptation allowed postoperative prostate-bed treatment, pelvic nodal irradiation and selective PSMA/MRI-guided boosting with relatively little new clinically significant bowel or urinary toxicity. The results are reassuring, but without a contemporary CT-guided control arm or patient-reported outcomes, they cannot establish that MR-guidance itself reduces toxicity or improves biochemical control.