title: Helical coil electrode radiofrequency ablation designed for application in osteolytic vertebral tumors--initial evaluation in a porcine model.
abstract: BACKGROUND
  Radiofrequency ablation (RFA) is emerging as a complementary treatment for vertebral metastases. Traditional RFA induces frictional heating leading to local tissue necrosis but often yields small, incomplete, and inhomogeneous zones of ablation in bone. We have developed a new bone-specific RFA electrode that uses a nontraditional frequency (27.12 MHz) and geometry (helical), exploiting a magnetic field and an electric field to generate larger and more comprehensive treatment zones.
  
  
  OBJECTIVE
  The purpose of the study was to evaluate the feasibility and safety of the Bone Coil RFA electrode in the spine.
  
  
  METHODS
  This is a preclinical in vivo study based on basic science.
  
  
  METHODS
  Under institutional approval, six healthy Yorkshire pigs received a sham and an RF treatment in two adjacent cervical vertebrae. To deploy the Bone Coil RFA device in dense porcine vertebrae, a surgical approach was required; an irrigated coring drill bit created a cylindrical path in the vertebral bodies through which the RFA electrodes were placed. The electronic circuit was completed by four grounding pads. Treatment was delivered for 10 minutes at 20 W (n=1), 25 W (n=1), and 30 W (n=4). To monitor the thermal rise and for safety, fiber-optic probes recorded temperatures in the center of each coil and near the spinal foramen. After the procedure, animals were monitored for 2 weeks. Magnetic resonance imaging (MRI) was completed immediately after treatment and at 14 days. Magnetic resonance image segmentation and histology were used to evaluate the ablation volume.
  
  
  RESULTS
  Comprehensive treatment of the porcine vertebrae was demonstrated by temperature monitoring, MRI, and histology. Large zones of RF ablation were obtained (RF: 3.72±0.73 cm3 vs. sham: 1.98±0.16 cm3, p<.05), confined within the vertebral body. Internal temperatures were elevated with RF (66.1 °C-102.9 °C), without temperature rise outside of the vertebrae (38.2 °C ± 1.5 °C). Mobility, neurological responses, and behavior were normal, consistent with preprocedural examination. Magnetic resonance imaging best visualized ablation at Day 14. Histology revealed comprehensive homogeneous coagulative necrosis with little peripheral sign of repair.
  
  
  CONCLUSIONS
  The Bone Coil RFA device created large intravertebral ablation volumes with no neurologic sequelae. Radiofrequency thermal ablation (clearly distinguished from the much smaller effects arising from core drilling) corresponded to the homogeneous necrosis visible on histology.
authors.affiliation: Institute of Biomaterials & Biomedical Engineering (IBBME), University of Toronto, Rosebrugh Building, RM 407 164 College St, Toronto, ON M5S 3G9, Canada; Sunnybrook Health Sciences Centre 2075 Bayview Ave, Room MG 371B Toronto, ON M4N 3M5, Canada.
authors.forename: Padina S
authors.initials: PS
authors.lastname: Pezeshki
authors.affiliation: Techna Institute, University Health Network, 124-100 College St, Toronto, Ontario M5G 1P5, Canada.
authors.forename: Sean R
authors.initials: SR
authors.lastname: Davidson
authors.affiliation: Institute of Biomaterials & Biomedical Engineering (IBBME), University of Toronto, Rosebrugh Building, RM 407 164 College St, Toronto, ON M5S 3G9, Canada; Techna Institute, University Health Network, 124-100 College St, Toronto, Ontario M5G 1P5, Canada.
authors.forename: Margarete K
authors.initials: MK
authors.lastname: Akens
authors.affiliation: Institute of Biomaterials & Biomedical Engineering (IBBME), University of Toronto, Rosebrugh Building, RM 407 164 College St, Toronto, ON M5S 3G9, Canada; Techna Institute, University Health Network, 124-100 College St, Toronto, Ontario M5G 1P5, Canada.
authors.forename: Kieran
authors.initials: K
authors.lastname: Murphy
authors.affiliation: Sunnybrook Health Sciences Centre 2075 Bayview Ave, Room MG 371B Toronto, ON M4N 3M5, Canada.
authors.forename: Claire
authors.initials: C
authors.lastname: McCann
authors.affiliation: Institute of Biomaterials & Biomedical Engineering (IBBME), University of Toronto, Rosebrugh Building, RM 407 164 College St, Toronto, ON M5S 3G9, Canada; Techna Institute, University Health Network, 124-100 College St, Toronto, Ontario M5G 1P5, Canada.
authors.forename: Michael
authors.initials: M
authors.lastname: Sherar
authors.affiliation: Institute of Biomaterials & Biomedical Engineering (IBBME), University of Toronto, Rosebrugh Building, RM 407 164 College St, Toronto, ON M5S 3G9, Canada; Sunnybrook Health Sciences Centre 2075 Bayview Ave, Room MG 371B Toronto, ON M4N 3M5, Canada.
authors.forename: Cari M
authors.initials: CM
authors.lastname: Whyne
authors.affiliation: Institute of Biomaterials & Biomedical Engineering (IBBME), University of Toronto, Rosebrugh Building, RM 407 164 College St, Toronto, ON M5S 3G9, Canada; Sunnybrook Health Sciences Centre 2075 Bayview Ave, Room MG 371B Toronto, ON M4N 3M5, Canada. Electronic address: albert.yee@sunnybrook.ca.
authors.forename: Albert J M
authors.initials: AJ
authors.lastname: Yee
mesh_terms: D000818:Animals; D017115:Catheter Ablation / Q000295:instrumentation*; D004566:Electrodes; D008099:Liver; D008279:Magnetic Resonance Imaging; D023421:Models, Animal; D009336:Necrosis; D010014:Osteolysis; D013131:Spine / Q000473:pathology* / Q000601:surgery*; D034421:Sus scrofa
keywords: Bone cancer; Bone metastases; Minimally invasive; Porcine; Preclinical; Radiofrequency ablation