Focused ultrasound surgery is emerging as a favorable alternative to existing treatments for liver cancer, although the technique still has to satisfy clinical trials.
The use of high-intensity ultrasound beams to kill small volumes of tumor cells in short bursts of energy has many advantages over conventional therapies, according to Dr. Gail ter Haar, head of therapeutic ultrasound at the Institute of Cancer Research, Sutton, U.K.
"The quest for cancer treatments into the new century will continue to pursue those that are not only effective, but also noninvasive in application, with low toxicity to normal tissues," she told the U.K. meeting on Imaging, Oncology, Science in Birmingham in May. "This is not a minimally invasive therapy, it is a noninvasive therapy. We don't have to insert any probes into the tumor. Our clinical trials are carried out without sedation or anesthetic."
Ultrasound ablation relies on thermal energy to "cook" small volumes of tumor cells in a short time. Temperatures in excess of 60 degrees C can be achieved during the one-second exposure. When sufficient energy is applied to a tightly focused ultrasound beam, all cells lying within the specific focal volume are killed, while those outside survive. The beam is moved mechanically to cover the whole tumor volume.
"Each shot, each exposure, destroys only a very small volume of tissue, and we are only exposing for one second, whereas RF procedures, for instance, are exposing a patient for 25 minutes," ter Haar said.
At Sutton's Royal Marsden Hospital, preliminary results from a phase I clinical trial of treatment for soft-tissue tumors, including prostate, liver, and kidney, are encouraging. Although patients occasionally reported moderate or severe pain from individual shots, at the end of the treatment, which involves up to 100 short blasts at 60-second intervals, no patient reported more than mild pain.
A phase II clinical trial for the treatment of liver metastases is now under way. Exciting noncancer applications are also possible, ter Haar said.
