Report from ARRS: Image-guided iceballs reliably kill kidney tumors

Percutaneous cryoablation of renal tumors is 100% effective, according to a report presented Monday at the American Roentgen Ray Society meeting.

Researchers at the Mayo Clinic in Rochester, MN, performed a retrospective study of 59 tumors treated with cryoablation since March 2003. The procedure is performed at Mayo on patients under general anesthesia using ultrasound guidance under the watchful eye of CT monitoring.

Between one and seven cryoprobes are inserted. If the tumor is visible, biopsy is performed with an 18-gauge needle. Of the 59 tumor treatment attempts, 57 were technically achieved. Of that number, follow-up imaging studies, taken on average nine months postablation, were available in 42 cases. All showed no tumor recurrence.

"Based on our early experience, cryoablation appears to offer an important alternative method of treatment for select patients. We need more long-term follow-up to prove durability and allow valid comparison with the surgical standard," said presenter Dr. Thomas Atwell, a radiologist at Mayo.

Atwell demonstrated cryoablation, as shown on CT images, during his presentation.

"CT shows how the probe is placed and ice forms around the probe within minutes. Postablation, the iceball grows until the tumor is completely covered by the iceball on CT," he said.

Success is defined as complete coverage of the tumor by the iceball on CT follow-up imaging, he said. The procedure is also effective in ablating tumors in adjacent structures.

"We can watch as the iceball literally grows from the probes and approaches other structures. Each probe can be adjusted individually," he said.

Cryoablation holds appeal for treating larger tumors, typically over 3 cm in size. The mean size of treated tumors in the Mayo Clinic study was 3.4 cm.

"In previous reports, people have struggled in treating larger tumors with radiofrequency ablation. With cryoablation, one can use multiple probes to treat larger tumors that are not amenable to RFA," Atwell said.

Referring physicians help determine who stands to benefit from cryoablation.

"We work well with our urologists. In general, it is older patients with a lot of comorbid disease or patients with a solitary kidney," he said.

In the Mayo Clinic study, the average patient age was 75 years, an older group than those who are typically candidates for surgical treatment.

"Young, healthy people go to surgery. The tumor winds up in a bucket where it should be," Atwell said.

Cryoablation proved safe for the most part, but there was a single significant adverse event. In that case, the tumor was large at 7.3 cm, and seven cryoprobes were inserted.

Subsequently, this patient underwent angiography, transfusion, and hospitalization.

"In general, the more probes we placed, the more bleeding we'd see," he said.

The study complication rate was 1.7%.