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Microwave Ablation of Hepatic Tumors Simultaneous Use of Multiple

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									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

           Department of Surgery
       University of Wisconsin Hospital
Rationale for Hepatic Ablation
 Resection is gold standard for hepatic
  tumors
 Hepatic tumor ablation increases the
  number of patients eligible for curative
  therapy
 Types of therapy
    Radiofrequency ablation

    Cryotherapy
Microwave Ablation
 Use of microwave energy to heat and kill
  tumors
 Theoretical advantages over radiofrequency
  ablation
    High Temperature

    Broad Field of Power Distribution

    Use of Multiple Probes
Multiple Probe Ablation
 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
                 • 13g, 15cm dipole antenna
                 • 60W, 915MHz generator
                 • 8 channels
                 • Fiber optic 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
 Lesions sectioned at 3mm intervals
 Digital image recorded of each section at
  600dpi
 Lesion dimensions calculated using ImageJ
  analysis software
    Diameter

    Volume
Assessment
   Multiple Probe lesions scored for shape
      Score    Criteria
      1        Discontinuous
      2        >25% Deflection
      3        10-25% Deflection
      4        <10% Deflection
      5        Round
Results
Results
                                 Lesion Diam eter


                    6

                    5
  Diam eter (cm )




                    4

                    3

                    2

                    1

                    0
                        Single Probe                Multiple Probe

                                        p<0.001
Results
                                 Lesion Diam eter
                                 Lesion Volum e


                    6.0
                    70

                    60
                    5.0
 Dim ension (cm )




                    50
  Volum e (cm 3)




                    4.0
                    40
                    3.0
                    30
                    2.0
                    20
                    1.0
                    10

                    0.0
                     0
                          Single Probe
                          Single Probe              Multiple Probe
                                         p<0.001
                                         p<0.001
Results
                            Lesion Volume by Measured Probe Separation
                Size by Separation
                 80
                 70
Volum e (cm 3)




                 60
                 50
                 40
                 30
                 20
                 10
                  0
                      0.0    0.5     1.0      1.5       2.0      2.5     3.0   3.5
                                       Average Probe Spacing (cm )
                                              r=0.24, p=0.43
Results
   Lesion Shape
Results
          Shape
    LesionLesion Shape by Measured Probe Separation
         6
         5
         4
 Shape




         3
         2
         1
         0
             0.0   0.5   1.0        1.5      2.0        2.5   3.0   3.5
                               Probe Separation (cm )
                                  r=-0.75, p=0.003
Results
                                    Tem perature

       Temperature
         140

                     120

                     100
    Volum e (cm 3)




                     80

                     60

                     40

                     20

                      0
                           Single Probe              Multiple Probe
                                          p = 0.42
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 1.5cm 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

								
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