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

Safety and Efficacy of Percutaneous Cryoablation for Recurrent or Metastatic Soft-Tissue Sarcoma in Adult Patients

BACKGROUND. Treatment options are limited in patients with recurrent or metastatic disease after initial treatment of soft-tissue sarcoma (STS) by surgical resection, radiation, or systemic therapy. Percutaneous cryoablation may provide a complementary minimally invasive option in this setting. OBJECTIVE. The purpose of this article was to assess the safety and efficacy of percutaneous cryoablation performed for local control of treatment-refractory recurrent or metastatic STS. METHODS. This single-institution retrospective study included adult patients who underwent percutaneous cryoablation from January 2016 to April 2023 to achieve local control of recurrent or metastatic STS after earlier treatment (surgery, radiation, or chemotherapy). For each treated lesion, a single interventional radiologist rereviewed intraprocedural images to assess for adequate coverage by the ice ball of the entire lesion and a 5-mm or greater margin in all dimensions. Complications and outcomes were extracted from medical records. The primary end point for procedure efficacy was 1-year local progression-free survival. RESULTS. The study included 141 patients (median age, 66 years; 90 women, 51 men) who underwent 217 cryoablation procedures to treat 250 recurrent or metastatic STS lesions. The most common STS histologic types were leiomyosarcoma (56/141) and liposarcoma (39/141). Lesions had a mean long-axis diameter of 2.0 cm (range, 0.4-11.0 cm). Adequate ice-ball coverage was achieved for 82% (204/250) of lesions. The complication rate was 2% (4/217), including three major complications and one minor complication. Patients' median postablation follow-up was 25 months (range, 3-80 months). Local progression-free survival rate was 86% at 1 year and 80% at 2 years. The chemotherapy-free survival rate was 45% at 1 year and 31% at 2 years. The overall survival (OS) rate was 89% at 1 year and 80% at 2 years. In Kaplan-Meier analysis, leiomyosarcoma, in comparison with liposarcoma, had significantly higher local progression-free survival but no significant difference in OS. In multivariable analysis, factors independently associated with an increased risk for local progression included inadequate ice-ball coverage (HR = 7.34) and a lesion location of peritoneum (HR = 3.63) or retroperitoneum (HR = 3.71) relative to lung. CONCLUSION. Percutaneous cryoablation has a favorable safety and efficacy profile in patients with recurrent or metastatic STS after earlier treatments. CLINICAL IMPACT. Percutaneous cryoablation should be considered for local control of treatment-refractory STS.

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

This work describes a sapphire cryo-applicator with the ability to sense tissue freezing depth during cryosurgery by illumination of tissue and analyzing diffuse optical signals in a steady-state regime. The applicator was manufactured by the crystal growth technique and has several spatially resolved internal channels for accommodating optical fibers. The method of reconstructing freezing depth proposed in this work requires one illumination and two detection channels. The analysis of the detected intensities yields the estimation of the time evolution of the effective attenuation coefficient, which is compared with the theoretically calculated values obtained for a number of combinations of tissue parameters. The experimental test of the proposed applicator and approach for freezing depth reconstruction was performed using gelatin-based tissue phantom and rat liver tissue in vivo. It revealed the ability to estimate depth up to 8 mm. The in vivo study confirmed the feasibility of the applicator to sense the freezing depth of living tissues despite the possible diversity of their optical parameters. The results justify the potential of the described design of a sapphire instrument for cryosurgery.

Prospective Margin Estimates Predict Local Tumor Progression Following Microwave Ablation of Small Renal Masses

PURPOSE

To evaluate the relationship between prospectively generated ablative margin estimates and local tumor progression (LTP) among patients undergoing microwave ablation (MWA) of small renal masses (SRMs).

MATERIALS AND METHODS

Between 2017 and 2020, patients who underwent MWA for SRM were retrospectively identified. During each procedure, segmented kidney and tumor shapes were coregistered with intraprocedural helical CT images obtained after microwave antenna placement. Predicted ablation zone shape and size were then overlaid onto the resultant model, and a model-to-model distance algorithm was employed to calculate multiple ablative margin estimates. LTP was modeled as a function of each margin estimate by hazard regression. Models were evaluated using hazard ratios and Akaike information criterion. Receiver operating characteristic curve area under the curve was also estimated using Harrell's and Uno's C indices (HI and UI, respectively).

RESULTS

One hundred and twenty-eight patients were evaluated (median age 72.1 years). Mean tumor diameter was 2.4 ± 0.9 cm. LTP was observed in nine (7%) patients. Analysis showed that decreased estimated margin size as measured by first quartile (Q1; 25th percentile), maximum, and average ablative margin metrics was significantly associated with risk of LTP. For every one millimeter increase in Q1, maximum, and mean ablative margin, the hazard of LTP increased 67% (HR: 1.67; 95% CI = 1.25-2.20, UI = 0.93, HI = 0.77), 32% (HR: 1.32; 95% CI 1.09-1.60; UI = 0.93; HI = 0.76), and 48% (HR: 1.48; 95% CI 1.18-1.85; UI = 0.83; HI = 0.75), respectively.

CONCLUSION

Prospectively generated ablative margin estimates can be used to predict the risk of local tumor progression following microwave ablation of small renal masses. LEVEL OF EVIDENCE 3: Retrospective cohort study.