Prognostic factors of biochemical recurrence and impact of pre-treatment MRI for prostate cancer radiotherapy.

Objectives: We conducted an analysis of the prognostic implications of MRI findings prior to radiotherapy in patients diagnosed with prostate cancer.

Methods: Patients from our institutional database who were treated with radiotherapy between 2014-2024 were searched for diagnostic MRI. The prognostic significance of PI-RADS score, index-lesion diameter, and Cancer of the Prostate Risk Assessment (CAPRA) score on biochemical recurrence was analysed.

Results: Of the 1480 patients, 499 (33.7%) underwent a diagnostic pre-treatment MRI; 49.5% were treated with low-dose brachytherapy, 29.8% with external beam radiation therapy (EBRT) plus a high-dose rate brachytherapy boost, and 20.7% with EBRT alone. Among the patients who underwent MRI, 404 (81%) had PI-RADS 4-5, including 35% with lesions ≥15 mm and 20% with lesions ≥20 mm. The median follow-up period was 44 months (IQR:23-66). Among the 78 patients who subsequently experienced biochemical recurrence, 16 underwent a diagnostic MRI prior to treatment. CAPRA score did not correlate with lesion diameter (P = 0.4). In univariate analysis, lesions ≥15 mm (P = 0.026) and ≥20 mm (P < 0.001) were significant predictors, as was CAPRA score (P < 0.001). In multivariate analyses, lesion size ≥20 mm (hazard ratio [HR], 3.49; 95%CI:1.25-9.76, P = 0.017) but not ≥15 mm significantly predicted recurrence. Stratified by CAPRA, only in high-risk cancers (score 6-10, 21% of patients) was a lesion ≥20 mm a significant predictor (P < 0.001).

Conclusions: We determined that a lesion on MRI with a diameter of ≥20 mm was an independent prognostic factor for biochemical recurrence, particularly in high-risk cancers. Whether the radiation dose-escalation of these lesions can improve clinical outcomes must be determined.

Advances in knowledge: We found that a prostate lesion on MRI with a diameter ≥20 mm was associated with poorer outcomes following radiotherapy.