BRIEF REPORT Percutaneous Microwave Ablation of Renal Tumors Using a Gas-Cooled 2.4-GHz Probe: Technique and Initial Results Jeremy C. Horn, MD, Rahul S. Patel, MD, Edward Kim, MD, F. Scott Nowakowski, MD, Robert A. Lookstein, MD, and Aaron M. Fischman, MD ABSTRACT The feasibility, safety, and preliminary effectiveness of microwave ablation (MWA) in the treatment of renal tumors using a high-powered, carbon dioxide–cooled probe were evaluated. There were 15 tumors treated in 14 patients. Computed tomography was performed immediately after MWA, and follow-up imaging was performed to evaluate for recurrence. Immediate technical effectiveness was 100%. One complication involved the formation of a renal artery pseudoaneurysm. At follow-up (mean interval, 12.5 wk) evaluation, 14 of 15 (93.3%) tumors demonstrated complete necrosis. MWA is a safe, effective treatment modality; larger studies are warranted to demonstrate long-term oncologic outcomes. ABBREVIATIONS CO 2 = carbon dioxide, MWA = microwave ablation, RCC = renal cell carcinoma The incidence of renal cell carcinoma (RCC) has been steadily increasing in the United States; the estimated number of new cases of cancers of the kidney and renal pelvis was 64,770 in 2012 (1). Traditionally, the “gold standard” of treatment for any nonmetastatic enhancing renal mass was radical nephrectomy; however, over the past 2 decades there has been a shift toward nephron- sparing techniques, including partial nephrectomy and thermal ablation for localized (T1) disease. This approach allows for cancer treatment while decreasing the risk of progression to chronic kidney disease. At the present time, the recommendation by the American Urological Association for management of a T1 renal mass is for partial nephrectomy, with either radical nephrectomy or thermal ablation considered appropriate alternative options (2), particularly in patients at high risk for progression to chronic kidney disease. Ablative techniques have the advantage of being able to be performed percutaneously, allowing discharge on the same day of the procedure and less operative time, without the inherent risks of open or laparoscopic surgery. Both cryoablation and radiofrequency (RF) ablation have been extensively studied for the treatment of localized RCC (3–6). Microwave ablation (MWA) is another ablative modality that has been demonstrated to be safe and efficacious in the treatment of small hepatocellular carcinomas (7). The investigation of its use in the treatment of RCC has been limited, but pre- liminary experiences have demonstrated high technical and clinical success (8–14). Numerous theoretical bene- fits of MWA over RF ablation have been well described (15) and include higher intratumoral temperatures and better conductivity in tissues with high impedance. Several studies have previously demonstrated larger ablation zones with MWA compared with RF ablation (16–18). Because the kidney is a highly vascular organ, the success of RF ablation can be limited secondary to & SIR, 2014 J Vasc Interv Radiol 2014; 25:448–453 http://dx.doi.org/10.1016/j.jvir.2013.10.029 Abstract presented at Annual SIR Meeting, New Orleans, Louisiana, April 2013. R.S.P. is a paid consultant for Arstasis and SIRTeX. F.S.N. is a paid consultant for Philips Healthcare. R.A.L. is a paid consultant for Cordis and MEDRAD, has given industry-sponsored lectures at Boston Scientific, is on the scientific advisory board of Boston Scientific, and is on the data safety monitoring board of W.L. Gore & Associates. A.M.F. is a paid consultant for Terumo Interven- tional Systems, Surefire Medical, and Celonova Biosciences and has given industry-sponsored lectures for Philips Healthcare. Neither of the other authors has identified a conflict of interest. From the Division of Interventional Radiology, Department of Radiology, Icahn School of Medicine at Mount Sinai, Mount Sinai Medical Center, One Gustave L. Levy Place, Box 1234, New York, NY 10029. Received June 15, 2013; final revision received October 16, 2013; accepted October 17, 2013. Address correspondence to A.M.F.; E-mail: aaron.fischman@mountsinai.org