The technique is being employed for an increasing number of therapeutic applications. And at the recent Radiological Society of North America (RSNA) annual meeting in Chicago, IL, researchers at the Mayo Clinic (Rochester, MN) reported on progress in two distinct applications of cryoablation.
First up, a study led by Mayo Clinic radiologist Thomas Atwell showed that cryoablation continues to deliver promising results for kidney-cancer patients. The team performed a retrospective review of 92 tumours treated in 91 patients using percutaneous cryoablation with CT monitoring. The tumours ranged in size from 1.5 to 7.3 cm, with an average of 3.4 cm.
Technical success - defined as coverage of the tumour by the ice ball during ablation, plus absence of tumour enhancement on CT or MRI performed within three months of treatment - was achieved in 89 of the 91 tumours. Follow-up evaluations at times ranging from three to 30 months (mean 13 months) were available for 62 patients, all of whom remain cancer free at last report.
The standard treatment for kidney tumours is surgery. This is highly effective, but generally has a longer recovery period than cryoablation. Insertion of the hollow needle only requires a quarter-inch incision and patients usually recover after one day in hospital, compared with several days for those who undergo surgery.
The researchers conclude that "percutaneous cryoablation of renal masses using CT monitoring is technically feasible and relatively safe." However, they caution that it's only recommended for patients who are poor candidates for surgery. Further follow-up studies are needed before the procedure can be widely applied. "This procedure appears to be a good option for some patients," said Atwell.
Pain control
While cryoablation is most commonly associated with destroying kidney and prostate tumours, it can also offer durable pain relief of cancer that has metastasized to bone. Such bone metastases can cause extreme pain that often cannot be managed by narcotics or other standard treatments. At RSNA, Mayo Clinic radiologist Matthew Callstrom presented the latest findings on cryoablation for pain management.
Callstrom and co-workers used cryoablation to treat 34 patients whose primary cancers had spread to the bone, and who had failed or refused conventional pain-management treatments such as radiotherapy or chemotherapy. The treatment involved insertion of a cryoprobe directly into the tumour under ultrasound or CT guidance. The patients were usually sedated for the procedure and released from hospital 24 hours later.
Eighty percent of this patient group experienced a clinically significant reduction in pain, with pain relief typically kicking in within a few days to four weeks. Furthermore, the treatment had a lasting effect: 24 weeks after undergoing the procedure, patients still reported significantly lower levels of pain.
"Cancer patients are living longer and we need to be able to manage their pain over a long period of time," said Callstrom. "Two key parts of this study are that the reduction in pain lasts and their quality of life improves after receiving the treatment." Importantly, this work shows that cryoablation worked after other treatments failed to provide adequate pain relief.
Callstrom recently received a $900,000 grant from the National Cancer Institute in the US to lead a randomized study comparing cryoablation and radiation therapy as treatment for pain associated with metastatic cancer.
Looking ahead
Both of the Mayo Clinic studies were performed using a cryoablation system from medical device company Endocare (Irvine, CA). Endocare's system uses the rapid expansion of argon gas in a sealed cryoprobe to freeze the tissue via the Joule-Thomson effect (in which the expansion of compressed gas through a small gap causes a drop in temperature).
But while Joule-Thompson-based cryoablation certainly has a lot to offer, the next big thing could be the use of near-critical nitrogen as a coolant. A near-critical-nitrogen-based cryoablation system can create an ice-ball faster than an argon-based system, helping physicians to reduce the time required for tumour ablation.
Near-critical nitrogen is a transition fluid, pressurized to the critical point at which gas almost becomes liquid. This unique fluid eliminates many of the challenges associated with liquid nitrogen - which requires relatively large-diameter (more than 3.5 mm) probes, is difficult to store efficiently and provides less control over the freezing process - while still benefiting from its strong freezing capabilities.
In 2006, Endocare received clearance from the US Food and Drug Administration to market its Cryocare CN2 - a near-critical-nitrogen-based cryoablation system. According to Endocare, with nitrogen more readily available and less expensive than argon in many countries, this new technology could drive the widespread adoption of cryoablation.
"We believe that physicians will welcome the nitrogen technology because it is easy to work with and delivers a colder, more powerful ice ball at the end of the probes," claimed Endocare's chairman and CEO Craig T. Davenport.
• See also Special report: advances in cryoablation on medicalphysicsweb.