Laser Interstitial Thermal Therapy for Spinal Metastases

In many patients with spinal metastases, stereotactic radiation therapy can provide effective local tumor control to prevent spinal cord compression and subsequent paralysis. However, in patients in whom a metastasis is touching or displacing the spinal cord, the tumor must be separated from the spinal cord before stereotactic radiation can be safely delivered. Until recently, this meant that such patients would have to endure an open surgery, along with its attendant potential complications and delays in other oncological treatment. But now a surgeon at The University of Texas MD Anderson Cancer Center is adapting an existing ablation method as an alternative to surgery to treat spinal metastases in select patients.

To avoid the risks associated with surgery for spinal metastases, Claudio Tatsui, M.D., an associate professor in the Department of Neurosurgery, has adapted a laser-based thermal ablative technique routinely used to treat tumors in the brain, prostate, liver, and other sites. The resulting procedure, spinal laser interstitial thermal therapy (SLITT), is currently performed only at MD Anderson.

Instead of having to surgically remove the portion of the tumor adjacent to the dura mater prior to stereotactic radiation therapy, Dr. Tatsui said, “We’re using a laser to heat and destroy the tumor in the epidural space and then covering the residual disease with stereotactic radiation therapy.”

Performing the procedure

In SLITT, a Jamshidi bone marrow needle is advanced into the spinal metastasis under magnetic resonance imaging (MRI)– or computed tomography–based guidance. The needle’s central trocar is removed, and a Kirschner wire is inserted through the needle. The Jamshidi needle is then removed, leaving the Kirschner wire to serve as a guide for placing an access cannula. Additional cannulas are usually placed; the number used depends on the size and location of the tumor.

For the ablation step, a laser probe is advanced to the end of the access cannula in the tumor, and the cannula is retracted slightly to expose the tip of the laser probe. The probe is then energized to heat the surrounding tissue to a temperature that irreversibly damages tumor cells (typically 50–74°C); the temperature at the interface between the tumor and vital structures is maintained at less than 50°C to avoid damaging those structures. The heating process is monitored in real time with MRI thermometry.

“What makes this procedure special is not the temperature itself, but the monitoring of the temperature in space,” Dr. Tatsui said. “The MRI lets me localize the temperature and treat lesions near vital organs without damaging those structures. We can find in real time where the heat is being applied, the extent of the damage, and if there is a need for additional laser probes.”

The heating process is repeated several times to ensure adequate thermal coverage of the tumor. The laser probe can deliver tumor-killing temperatures within a radius of 5–7 mm; and typically three access cannulas are needed per spinal lesion, although Dr. Tatsui said that he has used as many as eight cannulas for very large tumors. Preparing each cannula takes about 1 hour, but the ablation procedure itself takes only 3 or 4 minutes, depending on the complexity of the case. The procedure can be repeated as many times as needed if the tumor grows back.

As with traditional open surgery, SLITT is followed by stereotactic radiation therapy. But SLITT enables a much quicker return to treatment than does surgery. Whereas the median hospital stay following surgery is 7 days, that following SLITT is only 2 days, Dr. Tatsui said, noting that the procedure can also benefit patients for whom a long interruption in systemic treatment is not ideal.