Daily adaptive 1.5 T MR-Linac image-guided re-irradiation for prostate cancer: an international retrospective experience.

Abstract

BackgroundLocal recurrence in prostate cancer (PCa) after radical radiotherapy has become increasingly prevalent in the era of next-generation imaging. Meta-analyses suggest a favourable adverse event (AE) profile for stereotactic body radiotherapy (SBRT). This study aimed to evaluate the safety and efficacy of high-precision daily adaptive 1.5 T MR-Linac re-irradiation (re-EBRT).MethodsThis international retrospective study evaluated outcomes in patients with locally radio-recurrent PCa treated with adaptive SBRT re-EBRT on a 1.5 T MR-Linac platform. Eligible patients had biochemically or histologically confirmed radiological local recurrence within the previously irradiated prostate or prostate bed. Clinical characteristics, treatment, AE, and follow-up data were summarised using descriptive statistics and Kaplan-Meier methods.ResultsSeventy five patients were included across four centres. The median interval from primary radical therapy to recurrence was 79.0 months (IQR 56.2-126.5). Median PSA at initial presentation was 8.1 ng/mL (IQR 6.0-11.8), with a median PSA at recurrence of 2.2 ng/mL (IQR 1.0-3.6). Median age at re-EBRT was 73.3 years (IQR 68.5-77.7). MRI-guided adaptive radiotherapy (MRIgART) was delivered with hypofractionated regimens, most commonly 30 Gy in 5 fractions, with 46.7% receiving focal (GTV-only) and 53.3% whole-gland treatment. At 3 months, genitourinary AE were Grade 0-1 in 85.3% (64/75) of patients, Grade 2 in 13.3% (10/75) and Grade 3 AE in 1.3% (1/75). By 12 months, Grade 3 AE had risen to 12.5% (6/48), with no Grade ≥ 4 events. Gastrointestinal AE were mild, with no Grade 2 or higher events observed at any timepoint. Median post-re-EBRT follow-up was 11.9 months (IQR 3.5-21.1 months). Failure-free survival was 96.6% (95% CI 92.0-100.0) at 12 months and 76.5% (95% CI 62.8-93.2) at 24 months. The failures observed occurred within 24 months and were confined to intraprostatic/prostate bed or seminal vesicle sites.ConclusionsMRIgART re-EBRT is feasible for locally recurrent PCa, with acceptable gastrointestinal but non-negligible short to medium-term genitourinary toxicity.Data sharing statement: Research data are not available at this time. All centres subscribe to the MOMENTUM registry, from which data access requests can be made by participating centres.