Evaluation of a bipolar-cooled radiofrequency device for ablation of bone metastases: preclinical assessment in porcine vertebrae.

BACKGROUND CONTEXT: Cancer spread to the spine affects bone stability and can lead to pathologic fracture and neurologic impairment. Radiofrequency ablation (RFA) recently has gained popularity in treating skeletal tumors. Conventional RFA devices use a monopolar design, which limits the ability to comprehensively treat large tumors in bony tissues and may pose risks to adjacent critical normal neurologic tissues when applied to vertebrae. New bipolar-cooled radiofrequency (BCRF) may generate larger controlled lesions without the same degree of risk to adjacent structures.

PURPOSE: The purpose of this study was to evaluate the feasibility, efficacy, and safety of RFA with the use of a new bone-specific, BCRF probe in a porcine vertebral model and to evaluate the ability of magnetic resonance (MR) imaging to represent histologic outcomes of RFA treatment.

STUDY DESIGN: Basic science: preclinical in vivo study.

METHODS: RFA was evaluated in three noncontiguous lumbar vertebrae in six Yorkshire pigs (25-30 kg). Via a transpedicular approach for probe placement, two vertebrae received BCRF treatment and one vertebrae served as a sham control. MR imaging and neurological assessments were conducted pre- and posttreatment as well as immediately before animal sacrifice (n=3 at day 0, n=3 at day 14). MR ablation zones were compared with hematoxylin and eosin-stained histological sections.

RESULTS: With BCRF, large reproducible zones of ablation were achieved, confined within the vertebrae, without damage to adjacent tissues or the spinal cord. All animals demonstrated normal consistent neurologic behavior pre- and posttreatment. External tissue temperatures around targeted vertebrae were not increased. MR imaging after 14 days was more effective in demonstrating ablation effects than images on day 0, with radiologic findings most apparent on T2-weighted sequences. Histologic analysis of samples corresponded well to the zones of ablation observed on MR images (R=0.9, p<.01).

CONCLUSIONS: The study demonstrated feasibility, safety, and effectiveness of BCRF ablation of vertebral bone. This motivates ongoing preclinical evaluation in diseased models to further explore the potential for its use in clinical treatment of metastatic vertebrae.