LAUSR

OBJECTIVES To assess the qualitative and quantitative changes on prostate multiparametric magnetic resonance imaging (mpMRI) following partial gland ablation (PGA) with cryotherapy and correlate with histopathology. METHODS We used 3D Slicer to generate prostate models and segment ipsilateral (treated) and contralateral peripheral and transition zones in ten men who underwent MRI/transrectal ultrasound fusion-guided PGA during 2017-2018. Pre and post-PGA volumes of prostate segments were compared. Post-PGA mpMRI were categorized according to PI-RADS v2 and treatment response on mpMRI was assessed in a manner similar to the radiology evaluation framework following liver lesion ablation. RESULTS Median volume of ipsilateral peripheral and transition zones decreased from 10.9 mL and 13.0 mL to 7.2 mL and 10.8 mL (p=0.005), respectively. Median volume of contralateral peripheral and transition zones also decreased from 12.1 mL and 12.5 mL to 9.9 mL to 10.4 mL (p=0.005), respectively. Five men had clinically significant disease (Grade group ≥2) on post-PGA biopsy (three within treatment field and two outside). Of the men with clinically significant prostate cancer, mpMRI revealed PI-RADS 3 lesions in two. However, the treatment response framework did not detect residual disease. CONCLUSION PGA results in asymmetric and significant reductions in prostate volume. Our results highlight the need for a separate assessment framework to enable standardization of the interpretation and reporting of post-PGA surveillance mpMRI. Moreover, our findings have significant implications for MRI-targeted surveillance biopsy following PGA with cryotherapy.