Development of a Research Agenda for Percutaneous Renal Tumor Ablation: Proceedings from a Multidisciplinary Research Consensus Panel

Image-Guided Ablation of Renal Masses: Challenges to Produce High-Quality Evidence and Future Directions

Image-guided ablation (IGA) is a rapidly developing field in interventional oncology. There is some evidence suggesting IGA's non-inferiority compared with partial or radical nephrectomy for the treatment of small renal masses (SRM). However, these are mostly limited to retrospective cohort studies. This review article outlines the evidence comparing IGA to partial nephrectomy by collating the different survival measures and evaluates the challenges of producing clinical trials and high-quality evidence. The main challenges are due to the heterogeneity of SRM, patient selection bias, unstandardized endpoint and outcomes, and the lack of global practice standards. Despite the evidence thus far demonstrating that IGA stands as a non-inferior treatment modality for SRMs, exhibiting favorable short- and long-term outcomes, further robust research is needed to integrate ablation techniques into routine clinical practice with a multidisciplinary approach. There is emerging evidence that suggests randomized controlled trial in SRMs is possible, and technologies such as histotripsy as well as artificial intelligence are used in IGA.

Determination of the nonlethal margin inside the visible "ice-ball" during percutaneous cryoablation of renal tissue

OBJECTIVE

The study was designed to determine the distance between the visible "ice-ball" and the lethal temperature isotherm for normal renal tissue during cryoablation.

METHODS

The Animal Care Committee approved the study. Nine adult swine were used: three to determine the optimum tissue stain and six to test the hypotheses. They were anesthetized and the left renal artery was catheterized under fluoroscopy. Under MR guidance, the kidney was ablated and (at end of a complete ablation) the nonfrozen renal tissue (surrounding the "ice-ball") was stained via renal artery catheter. Kidneys were explanted and sent for slide preparation and examination. From each slide, we measured the maximum, minimum, and an in-between distance from the stained to the lethal tissue boundaries (margin). We examined each slide for evidence of "heat pump" effect.

RESULTS

A total of 126 measurements of the margin (visible "ice-ball"-lethal margin) were made. These measurements were obtained from 29 slides prepared from the 6 test animals. Mean width was 0.75 ± 0.44 mm (maximum 1.15 ± 0.51 mm). It was found to increase adjacent to large blood vessels. No "heat pump" effect was noted within the lethal zone. Data are limited to normal swine renal tissue.

CONCLUSIONS

Considering the effects of the "heat pump" phenomenon for normal renal tissue, the margin was measured to be 1.15 ± 0.51 mm. To approximate the efficacy of the "gold standard" (partial nephrectomy, ~98 %), a minimum margin of 3 mm is recommended (3 × SD). Given these assumptions and extrapolating for renal cancer, which reportedly is more cryoresistant with a lethal temperature of -40 °C, the recommended margin is 6 mm.