Luigi Solbiati, chairman of the Department of Radiology of the General Hospital, Busto Arsizio, Italy and director of the Interventional Oncology Radiology unit spoke to Interventional News about radiofrequency ablation and some of its limitations.
The context
We have been using radiofrequency ablation for many years – in fact, in my hospital, I was the first person to use the Cooltip system in 1995, as soon as it came out – so our experience with radiofrequency is extremely long. However, particularly in the field of metastases, we often have some limitations and problems. The critical issues include the absence of “oven effect”, variable size and shape of the necrosis area, and the blood vessel heat sink effect. There is a need to achieve large necrotic areas with large safety halos around the lesions, in order to try to avoid local tumour progression. And this, for radiofrequency, is sometimes very difficult to achieve. Ever since we have been testing microwaves, initially experimentally and now clinically, we understand that probably some of the limitations of radiofrequency in this particular field of metastases is likely be overcome by microwaves.
Why?
First of all, microwaves are more aggressive. You can maintain the antennae inside the lesion for a longer time than with radiofrequency. When you go on with an operation in the same position, the machine automatically stops; it does not work any longer. Microwaves tend to prolong activity, so tend to expand the amount of necrosis in time. Second, microwaves are much less sensitive to the “sink effect” caused by blood vessels, than radiofrequency. So when the metastatic lesions and, this is not rare are close to large blood vessels, radiofrequency has problems in treating the area close to the vessels. Microwaves do not care. They go on. So we have excellent examples of lesions entirely treated which are adjacent to blood vessels. When we started, we had some warning regarding the strength of microwaves for blood vessels. The concept was “ok, we can avoid the sink effect, but be careful, you could end up cooking the blood vessels and cause thrombosis”. So in the first period of experience, we were very cautious, very prudent, in order to avoid this.
Now we have a collection of cases of lesions, very close to the vessels, overtreated with the necrosis from the other side with the blood vessels totally viable and working in the middle of the volume of necrosis. And this was a very convincing result, because the danger of microwaves is not as great as it was thought to be before beforehand.
A word of caution…
But I do not recommend to all people with minimal experience or skill in ablation to start with microwaves, straight away. A learning curve period with RF is always suggested, but as soon as you develop experience and skill, probably in the field of metastatis, we will replace radiofrequency with microwaves in many cases. I cannot say in all cases, I cannot say in most cases, but in many cases, my sensation is that microwaves will allow us to overcome some of the limitations of radiofrequency ablation.
