Nagy Mekhail, MD, PhD
A new radiofrequency ablation (RFA) technique uses a bipolar water-cooled RFA probe to treat pain related to metastatic bone tumors when such pain is unresponsive to conventional methods. Clinical experience with cooled RFA (OsteoCool® RF Ablation System) at Cleveland Clinic shows local disease control, marked pain reduction and quality-of-life improvements from a single treatment, says Nagy Mekhail, MD, PhD.
Up to 30 percent of patients with metastatic bone tumors do not respond to palliative measures involving radiation therapy, chemotherapy, surgical excision or conventional RFA. Most RFA systems were designed for use in soft tissue, employing a monopolar technology. They do not perform consistently in bone because bone is not a good conductor of electrical energy and heat. The current from the single probe tip takes the path of least resistance to a grounding pad on the patient’s leg, explains Dr. Mekhail, Director of Evidence Based Medicine in the Department of Pain Management.
“Ideally, we’d like to produce a big lesion by burning the tumor and the surrounding trabecular bone,” he says. “Ablating the free nerve fibers can alleviate pain caused by vertebral body metastases.”
Current RFA systems produce lesions confined to the active tip. An internally cooled RFA probe lowers tissue impedance, increasing the radius of effective heating. Internal cooling eliminates the tissue charring that is common with conventional RFA. Transmission of RF waves ceases in charred tissue, limiting the size of the intervertebral lesion. The bipolar tip on the OsteoCool device localizes heating within cortical bone, eliminating the need for a grounding pad and reducing risk of damage to surrounding tissue.
“The lesion created by water-cooled RFA is spherical and extends beyond the probe tip on both sides,” says Dr. Mekhail. “It is eight times greater by volume than the thermal RFA lesion produced by a similar length probe. A large spherical lesion can effectively ablate the metastatic tumor and the free nerve endings that are causing the pain.”
The treatment is performed on an outpatient basis. Patients who have vertebral fracture as a tumor complication can undergo kyphoplasty in conjunction with cooled RFA.
To date, 11 patients have been treated with the OsteoCool system at Cleveland Clinic and the University of Washington in Seattle. Three patients who presented with severe low back pain despite opioid therapy — two with metastatic breast cancer to the L3 vertebral body, and one with vertebral metastasis secondary to prostate cancer — have been treated at Cleveland Clinic. All achieved a 75 percent reduction in pain on the visual analog scale as well as decreased disability and improved function, with an 80 percent improvement in Pain Disability Index score. Improvements were maintained at two- and six-month follow-up.
Enrollment in a study to test the Osteo-Cool system’s efficacy and safety in 15 patients with spinal metastases will begin at Cleveland Clinic soon, says Dr. Mekhail.