Andrew Wright MD, Chris Johnson, Fred Lee Jr. MD, and David Mahvi MD Microwave Ablation of Hepatic Tumors: Simultaneous Use of Multiple Probes Results in Large Areas of Tissue Necrosis Andrew Wright MD, Chris Johnson, Fred Lee Jr. MD, and David Mahvi MD Departments of Radiology and Surgery University of Wisconsin Hospital

Multiple Probe Ablation Microwave Ablation Goals Increase lesion size Increase control and customization of lesion size and shape Decrease treatment time Allow for treatment of multiple tumors

Hypothesis Multiple probe hepatic ablation will result in synergistically larger lesion sizes by shielding lesion center from blood-flow mediated cooling

Methods Microwave Ablation System • Vivant Medical 3.6cm length of actively radiating antenna • Vivant Medical • 13g, 15cm dipole antenna • 60W, 915MHz generator • 8 channels • Fiberoptic temperature monitor

Methods Microwave Protocol Domestic Swine 10 minute ablation, 40 Watts Single Probe Ablation Multiple Probe Ablation 3 parallel probes in triangular array Separation between probes varied from 0.5 to 3.5cm

Methods Microwave Protocol Single Probe Multiple Probe

Assessment Lesion dimensions calculated Multiple Probe lesions scored for shape Score Criteria 1 Discontinuous 2 >25% Deflection 3 10-25% Deflection 4 <10% Deflection 5 Round

Results

Results Single: 2.3  0.5 Multiple: 4.8  1.0

Results Single: 11.5  7.8 Multiple: 42.2  17.4

Results Size by Separation

Results Lesion Shape

Results Lesion Shape

Results Temperature Max T: Single 124oC Multiple 147oC

Results

Results 5 Probes

Conclusions Microwave ablation may be performed with multiple, simultaneous probes Microwave ablation with three probes results in lesions four times larger than single probe microwave ablation Confluent lesions may be produced with probe separations of 1.6cm or less

Summary Microwave ablation has several theoretical advantages over RF ablation Multiple probe microwave ablation may allow for treatment of larger, more complex tumors as well as simultaneous treatment of multiple tumors Multiple probe ablation may improve treatment of tumors near blood vessels