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

Why multiprobe RF?

Why multiprobe RF?

Why multiprobe RF?

Why multiprobe RF?

• 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)

Current RF systems

• Multiple prongs run at same voltage

RITA

RTC

Radionics

Faraday Effect

Faraday Effect

Electrodes at same voltage

Faraday Effect

Probes at different voltage=bipolar Current flows between probes

Faraday Effect

Electrically independent probes

How independent probes created

• Rapid switching between probes

• Temperature in tissue changes much slower than switching

• Temperature/impedance feedback algorithm

How independent probes created

Prototype dual probe unit

Prototype dual probe unit

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

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.

In vivo results

vs

Single Simultaneous dual RF

Note: same scale

In vivo results

• Time to temperature (100°C)

single: 2.7 minutes (162 seconds)

dual: 3.4 minutes (204 seconds)

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

In vivo results:max diameter

• Single: 3.3 cm

• Dual (each individual lesion): 3.8 cm

Conclusions

• Feasible to create multiple simultaneous burns with a single generator

• No lesion size penalty

• Slight increase in time to temperature

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