Longitudinal MRI changes after focal therapy for prostate cancer: cryotherapy vs. microwave tissue coagulation.

Purpose: This study compared the longitudinal changes in multiparametric magnetic resonance imaging (mpMRI) findings following lesion-targeted focal cryotherapy with those after microwave tissue coagulation (MTC) therapy for localized prostate cancer with the aim of determining their modality-specific imaging characteristics and evolution over time.

Materials and methods: The study included 16 patients (17 procedures) who underwent cryotherapy and 33 patients (34 procedures) who received MTC therapy between March 2017 and February 2024. Serial mpMRI scans were retrospectively reviewed for treatment-induced signal changes on T1-weighted imaging, T2-weighted imaging, diffusion-weighted imaging, and dynamic contrast-enhanced magnetic resonance imaging (MRI). Three radiologists independently reviewed the images, and interobserver agreement was evaluated.

Results: Early post-treatment MRI findings indicated distinct modality-specific patterns. Cryotherapy-treated lesions frequently demonstrated marked T1 hyperintensity, whereas MTC-treated lesions predominantly showed slight hyperintensity. On T2-weighted imaging and diffusion-weighted imaging, cryotherapy-treated lesions were characterized by hyperintensity with a hypointense rim, while MTC therapy was more likely to result in heterogeneous hypointensity. Early rim enhancement was common on dynamic contrast-enhanced MRI following cryotherapy (71.4%) and MTC (83.3%) and resolved by 23 and 41 months, respectively. In the late phase (> 12 months), imaging findings generally progressed toward fibrosis, which was characterized by hypointensity across all sequences without enhancement, although convergence timing varied from patient to patient.

Conclusions: While there are distinct modality-specific differences in MRI characteristics in the early phase after between focal cryotherapy and MTC therapy for localized prostate cancer, late-stage findings converge, primarily reflecting fibrosis. These MRI features can help when monitoring the treatment response and guide appropriate follow-up planning.