External validation of inter-reader reliability of the Prostate Imaging after Focal Ablation (PI-FAB) scoring system following focal cryoablation and focal high-intensity focused ultrasound.

Objectives: The efficacy of focal therapy (FT) has improved with the use of multiparametric MRI (mpMRI) for lesion identification, though standardized mpMRI reporting post-FT is lacking. The Prostate Imaging after Focal Ablation (PI-FAB) scoring system was recently introduced to standardize mpMRI interpretation for local recurrence post-FT. This study evaluates the diagnostic performance and inter-reader reliability of PI-FAB following cryoablation and high-intensity focused ultrasound (HIFU) modalities.

Materials and methods: This retrospective, single-institution study included all patients treated with FT from 2007 to 2023 with available follow-up mpMRI and subsequent prostate biopsy. Three fellowship-trained radiologists scored these images using the PI-FAB system. The primary objective was inter-reader agreeability of PI-FAB scores, and the secondary objective assessed performance metrics, including sensitivity, specificity, positive predictive and negative predictive value.

Results: 91 patients with 113 mpMRI exams (95 post-cryotherapy; 18 post-HIFU) were reviewed. There was substantial agreement between the readers (Fleiss' Kappa (κ): 0.71, p < 0.001; Gwet AC2: 0.70, p < 0.03). A PI-FAB score 3 had a significant ability to rule-in csPCa with high specificity (88%, 86%, and 93% per reader, respectively), and PI-FAB score 1 had high sensitivity to rule out csPCa (88%, 78%, and 84% per reader, respectively) in surveillance imaging (14-16 months median follow-up).

Conclusions: Our study suggests that the PI-FAB scoring system can be effectively used to evaluate mpMRI recurrence post-FT, with substantial inter-reader reliability and high specificity for predicting in-field clinically significant prostate cancer recurrence post-cryotherapy and HIFU. Larger, multi-institutional studies are essential to confirm PI-FAB's utility in clinical practice.

Key points: Question There is no widely accepted and validated standardized scoring system to predict the local recurrence of clinically significant prostate cancer after focal therapy with ablative modalities. Findings The Prostate Imaging after Focal Ablation (PI-FAB) scoring system effectively predicts in-field recurrence of prostate cancer after focal therapy with substantial inter-reader reliability and specificity. Clinical relevance As patient requests for focal therapy to treat localized low- to- intermediate risk prostate cancer become more common, based on its performance metrics, PI-FAB will aid in identifying in-field recurrence within this patient population.