Bone Targeted Radiofrequency Ablation (RFA) Electrodes for the Treatment of Appendicular and Vertebral Metastases

Bone metastases, an unfortunate and frequent occurrence in cancer, can result in skeletal related events, including pain, pathologic fractures, and hypercalcemia. Treatment strategies, such as surgery and/or radiation therapy, can be limited by invasiveness, maximum dose levels, and radio-resistivity. In this context, image-guided minimally invasive thermal treatment modalities such as radiofrequency ablation (RFA) have gained interest in the treatment of bone metastases. RFA conducts an alternating current through a probe placed within the tumour, resulting in ionic excitation of cells and frictional heating. RFA is reliant upon thermal and conductive properties of the tissue and leads to coagulative necrosis. Current technology developed and tested in soft tissues is limited by carbonization, small and unpredictable zones of ablation, particularly when used in bone. The lower conductive properties of bone tissue and proximity of bone to critical structures further challenge RFA application. This thesis focuses on design and evaluation of two novel bone-targeted RFA electrodes, a bipolar cooled RF (BCRF) and a solenoid-shaped (Bone Coil) RF probe, to improve the size and efficacy of RFA in bone. RFA was evaluated using healthy porcine and diseased lapine models with outcomes assessed through Magnetic Resonance Imaging (MRI) and histologic analysis of bone and tumour tissue. A cadaveric model was used to evaluate the role of RFA on spinal stability alone and in combination with vertebroplasty. Both BCRF and Bone Coil RF ablation were safe and effective in the spine. T2-weighted and contrast-enhanced T1-weighted MRI sequences two weeks post treatment were found to be most effective for image-based therapeutic evaluation. BCRF ablation yielded an eight-fold reduction in tumour volume in the rabbit femur. Treatment necrotized osteoblasts and osteoclasts comprehensively, whereas osteocytes were found to be more resilient to RFA. New bone formation and remodelling was observed at the ablation zone periphery. RFA alone led to reduced vertebral stability, but a restoration of strength and stability comparable to healthy levels was achieved when RFA treatment was combined with cement injection localized into the posterior portion of the vertebral body. Overall, this work motivates the future use of bone-targeted RF technology in the treatment of skeletal metastases.Ph.D