Freezing technology

Extremes of temperature have been put to use in medicine for decades. In electro-coagulation, heat is used to seal blood vessels during surgery in order to stop bleeding. An organ for transplantation is kept at 4⁰C in order to prolong its viability so that it can be transported to distant places for its eventual implantation. More recently, in the field of oncology, excessive heat or cold is used to destroy tumours. In the media, much has been written about radiofrequency destruction of tumours. In radiofrequency, heat is generated by passing electrical current through a special probe inserted into the tumour; the heat generated ‘cooks’ the tumour. The machine generating the heat is relatively cheap and small in size. It is easy to use and as such has become a very popular mode of treatment not only in oncology but also in other medical fields. Cryoablation is the complete opposite to radiofrequency ablation; the destruction of tissue / tumour is by freezing. Although cryoablation has been around for a much longer time than radiofrequency , it is less popular than radiofrequency ablation. The old technology involves passing liquid nitrogen through a probe placed in the tumour. This creates an ice ball and when the freezing is complete, you wait until the probe ‘warms up’ before it can be removed. The size of the probe is relatively big and overall the whole set up is quite cumbersome and not convenient to use. Consequently, it did not gain widespread popularity. In the last 2 decades, cryoablation technology has come of age. With new technology, the freezing and thawing is achieved instantaneously by the passage of helium and argon gas through the probe, the probe size is very similar to that for radiofrequency ablation and thus cryoablation is now as easy as to use as radiofrequency. (The only downside is that it costs much more than radiofrequency ablation.)

At the recent 34^th Annual Scientific Meeting of the Society of Interventional Radiology in San Diego, doctors from the Johns Hopkins Hospital reported the efficacy data from 90 cryoablation procedures on 84 patients with renal tumours, size 1 – 10 cm, performed between April 2006 and December 2008. They reported that 88 tumours were treated completely without any evidence of recurrence. Patients with tumours that were ≤ 4cm were the ones with a 100% response. In a sub-group analysis, these patients remained free of disease at 2.5 years. In another presentation at the same meeting, a group from Orlando, Florida presented their data on treating prostate cancer by focal cryoablation. Instead of adopting the approaches of watchful waiting or treating the whole prostate with radiotherapy / surgery, these doctors perform focal cryoablation of the prostate gland to treat the underlying cancer. (The approach is analogous to lumpectomy, instead of mastectomy, for the treatment of breast cancer.) Of 120 men treated over a 12-year period, 93% (112 patients) of these men have stable PSA level and no evidence of cancer after a mean follow-up of 3.6 years. (Seventy two patients were considered at medium or high risk for recurrence.)

The new cryoablation technology may take a while to find its niche in the field of medical therapy. When radiofrequency technology came along, many wrote off cryotherapy. Indeed, at a recent medical symposium held in a local university in Kuching, Malaysia, that I was speaking at, the head of the department of surgery asked the panel of speakers if he should consider acquiring a cryotherapy machine for treating liver and other tumours. One of the speakers opined that it would be a waste of time and money as it is not as good as radiofrequency ablation. I was not as adamant. [I was fortunate to have had experience with both radiofrequency and cryotherapy (both old and new technology) in treating liver tumours. If we remove the cost issue, I am quite convinced that cryotherapy will have a definite place in treating certain types of tumours. It will complement other treatment modalities such as radiofrequency ablation. In the meantime, we just have to be patient and await more studies on cryotherapy to better define its rightful place in medicine.