1 / 72

Developing New Technology for Local Tumor Control:

Developing New Technology for Local Tumor Control:. A Bioengineering Approach. Andrew Wright MD Department of Surgery 1/25/02. Background. Greater than one half of patients with colorectal cancer will develop liver metastases at some point in their clinical course

Samuel
Download Presentation

Developing New Technology for Local Tumor Control:

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Developing New Technology for Local Tumor Control: A Bioengineering Approach Andrew Wright MD Department of Surgery 1/25/02

  2. Background • Greater than one half of patients with colorectal cancer will develop liver metastases at some point in their clinical course • Surgical resection of an isolated liver tumor offers a five-year survival between 25 and 38%, compared to a 0% five-year survival without resection

  3. Only 10–20% of patients with liver tumors will have disease amenable to surgical resection due to high surgical risk or unfavorable anatomy Background

  4. Radiofrequency Ablation • High-frequency (460 kHz) alternating current flows from electrical probe through tissue to ground Probe insertion Extension of prongs RF current application

  5. Cool-Tip probe (17-gauge needle) (Radionics) Radiofrequency Ablation 12-prong “Leveen” probe, 4 cm diameter (Radiotherapeutics) 9-prong “Starburst” probe, 5 cm diameter (Rita Medical)

  6. TemperatureChange Heat loss through blood flow Thermal Conductivityand heat constant Current Density * Electric Field Constant Radiofrequency Ablation • Bioheat Equation • Lesion  (Energy Applied x Local Tissue Factors) – Energy Lost

  7. Finite Element Modeling • Determine material and electrical properties of tissue and ablation system • Develop geometric model • Solve Bioheat equation

  8. Finite Element Modeling

  9. Bioengineering Approach • Define Problem • Determine Possible Solutions • Model • Test • Refine

  10. RF RF Define Problem • Local recurrence as high as 30% • Uneven or irregular heating • Heat sink vessels Several mm’s

  11. Define Problem • Local recurrence as high as 30% • Uneven or irregular heating • Heat sink vessels • Difficult to treat large or multiple tumors

  12. Define Problem • Local recurrence as high as 30% • Uneven or irregular heating • Heat sink vessels • Difficult to treat large or multiple tumors • Poor imaging and localization Ultrasound B-scan After RF Ablation Ultrasound B-scan Before RF Ablation

  13. TemperatureChange Heat loss through blood flow Thermal Conductivityand heat constant Current Density * Electric Field Constant Possible Approaches • Bioheat Equation • Lesion  (Energy Applied x Local Tissue Factors) – Energy Lost

  14. Potential Solution #1 • Bipolar RF Ablation • Increase current density between electrodes • Increase energy deposition • More uniform tissue heating

  15. Bipolar RF Ablation

  16. Bipolar RF Ablation • FEM predicts nearly double lesion volume with bipolar electrode

  17. Bipolar RF • In vivo porcine liver Monopolar Bipolar

  18. Bipolar RF • Monopolar 3.93  1.8 cm2 • Bipolar 12.2  3.0 cm2

  19. Bipolar RF

  20. Bipolar RF Monopolar, d=2.3 mm Bipolar asymmetric, d=1.8 mm Bipolar symmetric, d=1.0 mm

  21. Bipolar RF • Problems • Inability to control two electrodes independently • Difficult technical placement • Unable to treat multiple tumors

  22. Potential Solution #2 • Multiple Probe RF Ablation • Allows overlapping treatment of large solitary tumors • Allows simultaneous treatment of multiple tumors

  23. Bipolar Monopolar Multiple Probe RF Ablation • Disadvantage: electrical shielding between electrodes (Faraday cage)

  24. Block diagram of system Multiple Probe RF Ablation

  25. Bipolar Monopolar Alternating Monopolar Multiple Probe RF Ablation

  26. Multiple Probe RF Ablation • Prototype Multiple Probe Device • Computer controlled electromechanical switch

  27. Multiple Probe RF Ablation • Ex Vivo Testing

  28. Multiple Probe RF Ablation • In Vivo Testing

  29. Multiple Probe RF Ablation Single Probe Ablation Simultaneous Multiple Probe Ablation

  30. Multiple Probe RF Ablation • In Vivo Testing • Lesion Volume • Single 10.7 cm3 • Dual 17.3 cm3 (per lesion) • Time to Target Temperature • Single 2.7 minutes • Dual 3.4 minutes

  31. Multiple Probe RF Ablation • Change to electrical switch • Increase number of probes • Increase speed of switching • Decrease load on generator • Evaluate synergism of overlapping multiple probe RF ablations

  32. Potential Solution #3 • Bioheat Equation • Lesion  (Energy Applied x Local Tissue Factors) – Energy Lost • Tissue Impedance (resistivity)

  33. Tumor Resistivity • Electrical properties of normal liver and tumor (K12/TRb) measured in an in vivo rat liver model

  34. Tumor Resistivity • Finite Element Model Tumor diameter = 2 cm

  35. Tumor Resistivity • Current Density 500 kHz 100Hz

  36. Tumor Resistivity • Temperature 500 kHz 100Hz

  37. Gray circle represents tumor boundary Tumor Resistivity • Lesion Difference

  38. Tumor Resistivity • Human? • Colorectal metastasis to liver

  39. Alternative Solution • Microwave Ablation • Theoretical advantages over radiofrequency ablation • No ground pad • Not limited by tissue charring and impedance changes • Use of Multiple Probes

  40. Microwave Ablation • Larger zone of active heating 1-2 mm MW 1-2 cm MW

  41. Microwave Ablation RF MW

  42. Multiple Probe Ablation • Null Hypothesis • Because microwave and radiofrequency ablation are both heat based, there will be no difference in ablation size or lesion pathology between the two technologies

  43. Methods • Microwave Ablation • Vivant Medical prototype system • 10 minute ablation, 40 Watts • Radiofrequency Ablation • RITA Medical Systems Starburst • 10 minute ablation, 3cm deployment 100oC target temperature

  44. Microwave Ablation System • Vivant Medical • 13g, 15cm dipole antenna • 915MHz generator • Fiberoptic temperature monitor

  45. Radiofrequency Ablation System • RITA Medical • 14g, 15cm expandable array • 460 kHz generator • Integrated thermocouple

  46. Lesion Volume * * * p=.02

  47. Lesion Length * ▪ ▪ ◦ * ◦ * p<.001 ▪ p=.02 ◦ p<.001

  48. Lesion Diameter

  49. 48o Pathology RFA MW Immediate 4 weeks

  50. Laboratory Data • No significant difference in AST, ALT, LDH, Alkaline Phosphatase, WBC, or HCT * * p<0.001

More Related