The Prognostic Value of PI-RADS Score in CyberKnife Ultra-Hypofractionated Radiotherapy for Localized Prostate Cancer

Simple Summary Magnetic resonance imaging is commonly used in pre-treatment prostate cancer diagnostics. The assessment includes a five-stage scale classification called Prostate Imaging-Reporting and Data System (PI-RADS), routinely used to describe the probability of finding a clinically significant cancer. Less is known about the association of PI-RADS score with patients' prognosis. Our retrospective study aimed to assess the association between pre-treatment PI-RADS score and risk of developing metastases, based on a cohort of 152 patients treated with ultra-hypofractionated CyberKnife radiotherapy for low or intermediate-risk group prostate cancer. PI-RADS score and the size of the target lesion proved to be significantly associated with the risk of developing metastases, suggesting that the introduction of PI-RADS score to initial risk assessment could improve the patient-tailored management of prostate cancer. Prostate Imaging-Reporting and Data System (PI-RADS) has been widely implemented as a diagnostic tool for significant prostate cancer (PCa); less is known about its prognostic value, especially in the setting of primary radiotherapy. We aimed to analyze the association between PI-RADS v. 2.1 classification and risk of metastases, based on a group of 152 patients treated with ultra-hypofractionated stereotactic CyberKnife radiotherapy for localized low or intermediate risk-group prostate cancer. We found that all distant failures (n = 5) occurred in patients diagnosed with a PI-RADS score of 5, and axial measurements of the target lesion were associated with the risk of developing metastases (p < 0.001). The best risk stratification model (based on a combination of greatest dimension, the product of multiplication of PI-RADS target lesion axial measurements, and age) achieved a c-index of 0.903 (bootstrap-validated bias-corrected 95% CI: 0.848-0.901). This creates a hypothesis that PI-RADS 5 and the size of the target lesion are important prognostic factors in early-stage PCa patients and should be considered as an adverse prognostic measure for patients undergoing early treatment such as radiation or focal therapy.