1. Multiprobe RF ablation: A Feasibility Study Fred T. Lee Jr., MD Dieter Haemmerich, MS Andrew S. Wright, MD David M. Mahvi, MD John G. Webster, PhD University of Wisconsin Depts. Of Radiology, Bioengineering, Surgery

2. Why multiprobe RF?

5. Simultaneous ablations –Increase lesion number –Multiple probes in large tumor Decrease ablation time Improve temperature distribution in lesion (make ablation more effective) Control lesion (bigger not always better)

6. Current RF systems Multiple prongs run at same voltage RITA RTC Radionics

7. Faraday Effect

8. Electrodes at same voltage

9. Faraday Effect Probes at different voltage=bipolar Current flows between probes

10. Faraday Effect Electrically independent probes

11. How independent probes created Rapid switching between probes Temperature in tissue changes much slower than switching Temperature/impedance feedback algorithm

12. How independent probes created

13. Prototype dual probe unit

15. Ex vivo results: Dual probes in pig liver at same temperature

16. Ex vivo results: Tissue at different temperatures (b) T1-T2

17. In vivo results Domestic pigs (n=3, mean wt=35 kg) 13 RF lesions –3 single control lesions –10 dual (5 pairs created simultaneously) RITA Model 150 generator (150 W), Starburst electrode deployed to 3.0 cm. 10 minute ablation, 100° C.

18. In vivo results vs Single Simultaneous dual RF Note: same scale

19. In vivo results Time to temperature (100°C) single: 2.7 minutes (162 seconds) dual: 3.4 minutes (204 seconds)

20. In vivo results:volume of necrosis Single: 10.7 cc Dual (each individual lesion): 17.3cc Therefore, 34.6 cc ablation obtained in approximately same time as 10.7 cc ablation

21. In vivo results:max diameter Single: 3.3 cm Dual (each individual lesion): 3.8 cm

22. Conclusions Feasible to create multiple simultaneous burns with a single generator No lesion size penalty Slight increase in time to temperature

23. What’s next? Increase # of probes (?4) Will require increased generator power Many technical factors involved with rapid switching (mechanical electrical) Cluster probes in close proximity to increase lesion size, temperature