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

Abstract 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 analyzed. Results Of the 1480 patients, 499 (33.7%) underwent a diagnostic pretreatment MRI. 49.5% were treated with low-dose brachytherapy, 29.8% with EBRT plus a high-dose rate brachytherapy boost, and 20.7% with EBRT alone. Among the patients who underwent MRI, 404 (81%) had PIRADS 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.