Calista Roen BSC, Presenter: Nothing to Disclose

Lisa Ann Sampson, Abstract Co-Author: Research Consultant, NeuWave Medical Inc

Meghan G. Lubner MD, Abstract Co-Author: Nothing to Disclose

J. Louis Hinshaw MD, Abstract Co-Author: Nothing to Disclose

Fred T. Lee MD, Abstract Co-Author: Stockholder, NeuWave Medical Inc, Madison, WI Patent holder, Covidien AG, Boulder, CO

Christopher L. Brace PhD, Abstract Co-Author: Shareholder, NeuWave Medical Inc Consultant, NeuWave Medical Inc

Radiofrequency (RF) ablation of cystic masses has been observed to be less effective than treatment of solid tumors, likely due to the limited heating of RF energy surrounding the electrode (1-2 mm). In contrast, microwave (MW) ablation heats a volume of tissue by rapidly oscillating water molecules within an electrical field that radiates 1-2 cm around the antenna. The purpose of this study was to compare heating between RF and MW systems in a cyst phantom to help determine the relative effectiveness for treating cystic tumors.

A tissue-equivalent agar phantom was created with a 4 cm diameter hollow inclusion, which was then filled with saline to mimic a cystic mass inside of the liver. One ablation was performed in each phantom using a single applicator for 10 minutes at 50 W. Three ablation devices were tested: a cooled-tip RF electrode (n=6); a deployable RF electrode (n=7 electrodes were deployed to contact the cyst wall); and a gas-cooled MW system antenna (n=7). Each device was positioned so that the expected ablation zone was centered in the cyst. Temperatures were recorded continuously using fiber optic sensors at the edge of the cyst wall, to monitor peripheral fluid temperatures, and 0.5 cm deep into the phantom, to monitor heating of the surrounding tissue phantom.

Mean (± st dev) peak fluid temperatures produced by the MW device (68 ± 6 ⁰C) were significantly greater than either RF system (deployable = 52 ⁰C± 3 ⁰C, cooled-tip = 48 ± 8 ⁰C; P<0.001). Cytotoxic fluid temperatures were achieved in 7/7 samples with the MW system. Similarly, temperatures produced by the MW system were significantly greater in the tissue phantom than the cooled-tip RF group (deployable = 43 ± 11 ⁰C P>0.05, cooled-tip = 36± 7 ⁰C; P<0.01).

The MW system more effectively heated the cyst phantom than deployable or cooled-tip RF systems. MW ablation may be a more effective treatment than RF for treatment of cystic masses. Additional preclinical and clinical studies are needed to verify these results.

This study suggests that microwaves may be more effective than RF for the treatment of cystic masses such as cystic renal cell carcinoma.

Roen, C, Sampson, L, Lubner, M, Hinshaw, J, Lee, F, Brace, C, Thermal Ablation in Cystic Lesions: Microwaves Improve Heating When Compared to Radiofrequency Ablation in a Phantom Model.  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9015613.html