The effects of localized cold work on the heating characteristics of thermal therapy implants

The use of cylindrical palladium-cobalt alloy rods has proven effective in the clinical ablation of prostate cancer. In order to thermally destroy tissue, the ferromagnetic implants must heat to temperatures greater than 42 degrees C and produce a power output of at least 400 mW. However, localized cold work such as bending may effect the heating characteristics of these rods and have detrimental clinical effect. Three different types of test devices were manufactured to introduce cold work at one point in the implant: a sharp bend, a curvature, and an MTS three-point bend. After bending, each rod was then restraightened. Rod power output before and after bending was measured by calorimetry. Statistical comparison of power output for prebent and restraightened rods versus degrees bent was performed through the use of the SAS MIXED procedure to fit a mixed-model repeated-measures ANOVA with the use of multivariate models. In vitro testing showed that there was only a small change in the power output before and after rods were cold worked regardless of the type of bending. Therefore, localized cold work does not affect the clinical heating characteristics of rods.