The clinical application of prostate magnetic resonance imaging for local recurrence reporting in histologically confirmed prostate cancer recurrence after radical radiotherapy.

[OBJECTIVES] To determine if histologically confirmed tumours were categorized as highly suspicious according to Prostate Magnetic Resonance Imaging for Local Recurrence Reporting (PI-RR). Moreover, additional diffusion-weighted images/apparent diffusion coefficient (DWI/ADC) and dynamic contrast-enhancement parameters were analysed for more precise diagnosis.

[METHODS] A single-centre retrospective study on 145 patients (aged 70.8 ± 6.8) with prostate cancer recurrence after radiation therapy. Patients underwent multiparametric magnetic resonance imaging (mpMRI) and biopsy (2007-2021). We employed nonparametric tests and Receiver operating characteristic (ROC) curves to determine the diagnostic value of the ADC parameter.

[RESULTS] Most patients 127 (87.6%) had a high and very high likelihood of local recurrence (PI-RR 4-5), while 18 (12%) had PI-RR 2-3. The ADC value of 1.13 × 10-3 mm2/s best differentiated between benign and malignant lesions (ROC AUC 0.859). PI-RR 2 and 3 scores were found in 2 and 16 patients, respectively. Of these lesions, 12 showed low ADC (<1.13 × 10-3 mm2/s), which could be considered malignant. As regards the enhancement curve, 6/18 had wash-out, 6/18 had plateau. Only 6/18 lesions had persistent curve enhancement (potentially benign). Considering ADC and enhancement curve type, only 2 lesions did not meet the criteria for malignancy.

[CONCLUSIONS] Most patients (87.6%) had a high or very high likelihood of local recurrence (PI-RR score 4 or 5). In patients with PI-RR ≤3 scores, the ADC value and the enhancement type may allow for better classification of lesions with a high risk of recurrence.

[ADVANCED IN KNOWLEDGE] Detailed mpMRI evaluation can estimate prostate cancer recurrence risk with very high accuracy using PI-RR score, the ADC value, and the enhancement curve type.