An Update on Microwave Ablation With David J. Breen, MRCP, FRCR

IO360: Tell us about your facility and your practice.

Breen: I am an interventional radiologist with Spire Southampton University Hospital in the United Kingdom. There is a large interventional oncology practice within the UK, and in terms of covering all modalities, our facility offers possibly the broadest array of interventional oncology treatments currently available, including microwave ablation, cryoablation, transarterial chemoembolization, and yttrium-90.

IO360: What is new in the world of microwave ablation?

Breen: Certainly in our own practice, we’ve moved on from radiofrequency ablation to microwave ablation simply because radiofrequency ablation was too reliant on passive thermal conduction and that led to poor predictability and local recurrences. Microwave is more robust, as we’ve been saying for a few years. 

Also, a few new developments are occurring in microwave. For one, the probe design is improving. We are not seeing the probe failures that we used to see maybe 4 or 5 years ago. There is better cooling of the probe shafts, enabling more effective treatments. Some of the companies have brought the feed point back down toward the tip of the probe so you don’t have a big ceramic spike on the front of the probe, which allows us to treat in tighter corners and up against critical strictures better. 

One company has redesigned its probe to send the perfusate down the shaft and all the way around the actual microwave feed point. The manufacturer argues that in so doing they have maintained the consistency of the environment around the metallic microwave source so that it doesn’t modulate the wavelength, and thereby the propagation of the active zone of the microwave, through tissue desiccation and gas formation. We have yet to see if that’s borne out in practice, but the company claims more consistent time and power against volume achieved with this device. I think that’s an interesting claim, because sphericity of the ablation zone is part of the Holy Grail of predictable tumor ablation. 

Another important development, which is almost adjunctive to microwave, is prediction and planning of treatments, akin to radiotherapy. I’m still hesitant about planning and prediction of ablation zones, and we don’t tend to use some of the execution devices, like tip tracking and laser guidance, but the key software development is ablation confirmation using image fusion. This can be CT over CT or potentially MR over MR. In this way we look at the ablation zone achieved, register that correctly with the tumor target, and confirm electronically that we have A0 margin or negative margins. This achieves electronic confirmation of “surgical” margins. We must talk to the engineers and understand the plasticity of tissue. Also, when you do image registration, you get into some quite technical discussion about rigid registration versus elastic deformable registration versus semi rigid registration and that will allow us to confirm quickly and during the course of the procedure that yes, the job is done with safe margins, I can pull out, and we’ve achieved a good outcome. I believe this will be an important tool for reducing local recurrences down to a minimum, hopefully reaching equipoise with surgery for the liver. 

IO360: You have said that you believe clinicians should ask themselves whether microwave ablation devices need to be improved or if their own technique should be improved. Could you expand on that?

Breen: The companies have been working hard these last few years and certainly devices are producing larger ablation zones. But we all know it’s not about bigger and bigger ablations, it’s about predictability. To some extent, I think one or two of the technologies are beginning to yield better prediction against time in the in vivo setting. I think sometimes we’ve got to stop looking to the companies to provide a new toy and instead ask ourselves whether our own practice is diligent enough to reduce local recurrences and be sure that we achieve what we set out to achieve. 

One of the things that is striking to me as I visit other institutions is that there is an enormous range of practice in terms of image guidance, general anesthetic versus conscious sedation, the number of iterations, the use of multipolar microwave. All of these steps are subtle, but they impinge upon outcome. Maybe one unit has local recurrence rates of 30% or more and another unit for the same disease has local recurrences of 5%. Now the question is, why? 

We’ve got to come to grips with quality control. The interesting analogy I found is with radiotherapy whereby one of the biggest benefits of running multicenter trials was the attention to quality control. That’s the same problem that we could and should be interested in for microwave ablation. I think there’s a real scope for improved diligence and thereby improved outcome.

Suggested citation: Ford J. An update on microwave ablation with David J. Breen, MRCP, FRCR. Intervent Oncol 360. 2016;4(4):E70-E71. 

Dr. Breen reports no related disclosures.