Guided thermal ablation topples adoption barriers

The swift rise of percutaneous ablative interventions represents one example of the power of innovation-and how it can crush barriers that stand between discovery and adoption.

In his 2006 Pendergrass Lecture at the RSNA meeting, Dr. William Charboneau, a radiologist at the Mayo Clinic in Rochester, MN, traced the past, present, and future trajectory of percutaneous ablative interventions. As with radiology as a whole, innovation is the key to the field's continued success, he said.

"When you look at how far we've come in just 10 short years and imagine where we will be in another 10 or 20 years, it is quite exciting," Charboneau said.

Percutaneous ablation has transformed patient management on several fronts. One case cited by Charboneau involved a patient who underwent nephrectomy to treat right renal cell carcinoma. Open surgery produced a scar that extended from the patient's flank to midline. He was hospitalized for five days and needed 35 days to recover. The procedure cost $33,000.

Three years later, the patient underwent radiofrequency ablation for the same disease in his left kidney. This time, intervention produced a skin puncture that was covered with a bandage. He was discharged after one day and recovered two days later. Normal renal function was restored to his surviving kidney. The procedure cost $7000.

"This is the kind of case that gives you a sense of the value for this therapy in day-to-day medicine," Charboneau said.

Such experiences have fueled explosive growth for ablative cancer therapy. Utilization at the Mayo Clinic rose from nine procedures in 1997 to 245 procedures in the first 11 months of 2006, he said. In terms of scholarship, about 450 abstracts were submitted to the RSNA under the topic of tumor ablation in 2006; only a handful were submitted in 1996.

Buoyed by such successes, image-guided interventional oncology is headed in three directions, Charboneau said: more precise treatments, adoption of better treatment devices, and combined therapies that simultaneously exploit the strengths of several technologies.

Limitations, such as the inherent imprecision of accepted pretreatment planning techniques, will be addressed, he said. For example, preprocedural CT and MRI used for planning are often performed weeks before an intervention with the patient in a supine position, which is often inappropriate. He predicted that better protocols inspired by methods first developed for radiation therapy will be applied to ablative therapy planning. These techniques include computer software for isolating targeted tissue as well as computer simulations.

Better treatment devices will also be adopted. Cryoablation is gaining popularity because it is more accurate for margin containment than RFA, he said. Microwave ablation will produce sharper margins and more spherical ablation volumes than RFA. Electronically steerable antennas may allow interventionalists to ablate predefined asymmetrical volumes to improve targeting. Focused ultrasound also shows great potential, along with combined therapies, such as embolization and chemoembolization and focused ultrasound and cryoablation.

None of the current options for image guidance, including ultrasound, CT, or MR, provide an ideal solution for needle guidance, so researchers are developing multimodality approaches to compensate. Fusion strategies include a method for reformatting baseline axial CT imaging to conform to real-time ultrasound and CT. Developed in Italy, the technique should be ready for adoption in three years.

Robotic devices, such as the da Vinci surgical system, will help improve the precision of needle guidance in small lesions and multiple needle insertions to ablate large lesions. Targeted drugs, such as liposomal doxorubicin and other heat-activated drugs, will help boost the tumor-killing effectiveness of thermal treatment.

Heat shock protein, a stress protein released after sublethal thermal damage, has attracted great interest, Charboneau said. Phase II trials are under way in immunology and oncology to test its effectiveness for melanoma and renal cell carcinoma. Complex ex vivo methods of harvesting and cultivating a patient's heat shock protein could be improved using ablation to produce it in vivo.

A preliminary human clinical trial at the Mayo Clinic has been approved for nine patients with melanoma and renal cell carcinoma to test the technique. Sublethal heating with a conventional RF device will be directed to renal cell carcinoma to stimulate the release of heat shock protein. The immune system will then be stimulated with granulocyte-macrophage colony-stimulating factor, leading the heat shock protein to migrate through the lymphatic system to lymph nodes. White blood cells harboring surface antigens targeting renal cell cancer cells will be released to kill cancer cells in the primary tumor and distant metastases, he said.