Temporal changes in MRI appearance of the prostate after focal ablation

Abstract

Purpose: The purpose of our study was to retrospectively evaluate and categorize temporal changes in MRI appearances of the prostate in patients who underwent focal therapy with MRI follow-up. Methods: The Institutional Review Board approved this retrospective study and waived the requirement for informed consent. Thirty-seven patients (median age 61; 48–70 years) with low-to-intermediate-risk, clinically organ-confined prostate cancer underwent focal ablation therapy from 2009 to 2014. Two radiologists reviewed post-treatment MRIs (n = 76) and categorized imaging features blinded to the time interval between the focal therapy and the follow-up MRI. Inter-reader agreement was assessed (kappa) and generalized linear regression was used to examine associations between an imaging feature being present/absent and days between ablation and MRI. Results: Inter-reader agreement on MRI features ranged from fair to substantial. Edema was found present at earlier times after ablation (median 16–25 days compared to MRIs without edema, median 252–514 days), as was rim enhancement of the ablation zone (18–22.5 days vs. 409–593 days), a hypointense rim around the ablation zone on T2-weighted images (53-57.5 days vs. 279–409 days) and the presence of an appreciable ablation cavity (48.5–60 days vs. 613–798 days, all p < 0.05). Enhancement of the ablation zone/scar (553–731 days vs. 61.5–162 days) and the formation of a T2-hypointense scar were found to be present on later MRI scans (514–553 days vs. 29–32 days, one reader). Conclusions: The MRI appearance of the prostate after focal ablation changes substantially over time. Identification of temporal patterns in the appearance of imaging features should help reduce image interpretation variability and errors when assessing post-therapeutic scans.