VANCOUVER – Cancerous tumours are being engulfed within ice balls, then thawed and frozen again until they wither and die as part of a new technique being pioneered at Vancouver General Hospital.
The process involves sending argon gas through long thin hollow needles into tumours, plunging the cancer cells to temperatures of -100 Centigrade, then thawing the cells with helium gas.
"The tumour cells are killed by the combination of freezing and thawing. The freeze, thaw, freeze cycle results in complete tumour cell disruption," said Dr. Peter Munk, an interventional musculoskeletal radiologist at VGH.
Called percutaneous cryoablation, the technique is being explored as a less painful alternative to some other procedures used to deal with cancer. And because the ice ball that surrounds the tumour is visible to surgeons, they can track what is happening to it as well as avoid injury to surrounding tissue and organs.
A pilot project to evaluate the safety and efficacy of the procedure is expected to begin at VGH in a few months after final approvals from a University of B.C. ethics review panel.
The project will involve up to 15 patients with metastatic disease -cancer that has spread to muscle and bone -who need help to relieve extreme pain, said Munk.
Pain can be severe for such patients and conventional therapy, such as radiation or pain medications, may not be effective, he said. The new technique can also be used to either cure or treat the pain associated with liver, lung or kidney tumours.
"With the cryo method, it’s less painful than other procedures because it involves freezing," said Munk.
"It has an anesthetic, numbing effect. Patients can get a local freezing before the probes go in, and a sedative, and then they can leave after the procedure."
He noted that other methods -such as radio-frequency ablation, which uses heat -may require a general anesthetic, requiring patients to stay in hospital for a few days after.
Another major advantage was cited by University of Wisconsin doctors in a 2008 study describing a series of cases involving cryoablation.
They noted the ice ball that surrounds the tumour is visible on CT scanning technology, which means that tumour death can be observed, as can the status of surrounding structures, like nerves and organs. That is important because doctors don’t want to damage such nerves and organs.
The study also said cryoablation appears to be less painful than other methods, not only during the procedure, but in the immediate aftermath.
The process involves using CT scanning technology as an imaging guide to insert needlelike probes through the skin to the targeted tumour.
The insulated probes are connected to a generator box that provides the argon gas that then flows through the steel tubes. Most tumours require the placement of multiple probes positioned at different angles. The temperature at the uninsulated tips of the probes drops to -100 Centigrade.
After a certain length of time, the frozen tissue is then thawed by helium gas passed through the same probes, and then the freezing cycle is repeated.
Although the cost of each case varies, Munk concedes it is expensive because the $1,000 probes are disposable (one use only) and several might be required for each case. Although the capital cost of the generator box is relatively inexpensive ($50,000), other costs, which can add up to many thousands of dollars, relate to the medical and CT technology staff required.
The cost of the Vancouver Coastal Health Research Institute study will be sponsored by Galil Medical, which manufactures the equipment acquired by VGH with donor funds. Munk’s collaborator in the study is Dr. Paul Clarkson, an orthopedic surgeon who specializes in bone and soft tissue cancers.
Dr. Stephen Ho and Dr. David Liu are interventional radiologists at VGH who have also started using the method.
Cryoshock causing death is the most serious adverse effect that has been described in the medical literature about the technique.
But Munk, who is editor of the Canadian Association of Radiologists Journal, said of the 30 patients who have had cryoablation at VGH since the technology was acquired last year, there have been no serious complications during or after the procedures.
The benefit of the trial is that the cases will be documented and the data peer reviewed and published for close examination of the results.
Sun Health Issues Reporter
pfayerman@vancouversun.com
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