Abstract No. 492 Adjacent metallic instrumentation does not limit bone ablation when using a bipolar radiofrequency device

Abstract

An unproven theory that has favored radiotherapy and limited wider application of first-line ablation for patients with painful metastatic bone tumors is the belief that adjacent metallic instrumentation impairs outcomes for local tumor control by serving as a heat sink. This theory has not been tested with modern bipolar radiofrequency (RFA) systems FDA cleared and specifically calibrated for bone ablation. The current study challenges a commercially available bipolar RFA device maximally, with a screw interrupting the center of the return circuit, to determine effects on ablation zone size and temperature, as well as assess whether titanium versus stainless steel instrumentation has different effects, and whether the instrumentation heats sufficiently to create nontarget ablation. Ex vivo ablations were performed using freshly harvested pig vertebrae. Image-guided RFA probe placement and screw placement allowed preparation of 15 vertebrae for ablations, 5 with no screw (control), 5 with adjacent orthogonal titanium screw, and 5 with adjacent orthogonal stainless steel screw. 3 Watt RFA was performed for 5 minutes or until impedance stopped the ablation automatically. Real-time temperature measurements were obtained from the built-in thermocouple in the RFA device and an additional thermocouple on the adjacent screw when applicable. Vertebrae were ananlyzed with 3-Tesla MRI, gross sectioning and histopathology. At 5 minutes, ablation zone temperatures increased mean 21.5 ± 2.1, 20 ± 2.9, 17.2 ± 3.5°C (control, titanium, steel respectively, P = 0.3, one-way ANOVA; P = 0.09, linear regression). At 5 minutes, screw temperatures increased mean 0.3 ± 1°C (titanium, P = 0.6, paired t-test), 4.6 ± 2.9°C (steel, P = 0.023, paired t-test). MRI, gross, histopathology confirmed ablation contained and extended beyond any screws. Adjacent metallic instrumentation did not significantly limit ablation in this experiment using a bipolar RFA device. The stainless steel screw demonstrated statistically significant heating by approximately 5 degrees Celsius at 5 minutes of a low power (3 Watt) RF cycle. These findings support further in vivo study to assess the short-term biologic response and remodeling with juxta-metallic bone RFA.