Intraoperative MRI-derived volumetric ablation margins and initial correlation with local outcome after MRI-guided cryoablation of renal tumors

Abstract

Purpose To assess volumetric ablation margins derived from intraoperative pre- and post-ablation MRI after magnetic resonance imaging (MRI)-guided percutaneous cryoablation of renal tumors and explore its correlation with local treatment success. Methods Retrospective analysis was performed on 30 patients (mean age 69y) who underwent percutaneous MRI-guided cryoablation between May 2014 and May 2020 for 32 renal tumors (size: 1.6–5.1 cm). Tumor and ice-ball volumes were segmented on intraprocedural pre- and post-ablation MR images using Software Assistant for Interventional Radiology (SAFIR) software. After MRI-MRI co-registration, the software automatically quantified the minimal treatment margin (MTM),defined as the smallest 3D distance between the tumor and ice-ball surface. Local tumor progression (LTP) after cryoablation was assessed on follow-up imaging. Results Median follow-up was 16 months (range: 1–58). Local control after cryoablation was achieved in 26 cases (81%) while LTP occurred in 6 (19%). The intended MTM of ≥5 mm was achieved in 3/32 (9%) cases. Median MTM was significantly smaller for cases with (− 7 mm; IQR:-10 to − 5) vs. without LTP (3 mm; IQR:2 to 4) (P < .001). All cases of LTP had a negative MTM. All negative treatment margins occurred in tumors > 3 cm. Conclusions Determination of volumetric ablation margins from intraoperative MRI was feasible and may be useful in predicting local outcome after MRI-guided renal cryoablation. In our preliminary data, an intraoperative MRI-derived minimal margin extending at least 1 mm beyond the MRI-visible tumor led to local control and this was more difficult to achieve in tumors > 3 cm. Ultimately, online margin analysis may be a valuable tool to intraoperatively assess therapy success, but larger prospective studies are needed to establish a reliable threshold for clinical use.

Manufacturing of Sapphire Crystals with Variable Shapes for Cryosurgical Applications

“…Particularly, it ensures higher rate of tissue freezing, higher ice-ball volume and lower temperatures. Finally, such applicators can be additionally assisted with optical monitoring [8], which allows to overcome one of the main problem of cryosurgery, that is the uncontrollable tissue damage [36,43,44].…”

Optical Sensing of Tissue Freezing Depth by Sapphire Cryo-Applicator and Steady-State Diffuse Reflectance Analysis

“…The evident drawback of this approach is the absence of real-time monitoring of tissue freezing. Therefore, it is desirable to use other techniques for monitoring, such as ultrasound (US) [ 19 , 20 ] and magnetic resonance imaging (MRI) [ 21 , 22 , 23 ], computed tomography (CT) [ 24 , 25 ] and temperature measurements [ 26 ]. Visualization by US, CT and MRI requires additional sensors or even expensive systems that can not be combined with the cryosurgical instrument.…”