Intracranial hyperthermia through local photothermal heating with a fiberoptic microneedle device

Background and Objectives The fiberoptic microneedle device (FMD) seeks to leverage advantages of both laser-induced thermal therapy (LITT) and convection-enhanced delivery (CED) to increase volumetric dispersal of locally infused chemotherapeutics through sub-lethal photothermal heat generation. This study focused on determination of photothermal damage thresholds with 1,064nm light delivered through the FMD into in vivo rat models. Materials and Methods FMDs capable of co-delivering laser energy and fluid agents were fabricated through a novel off-center splicing technique involving fusion of a multimode fiberoptic to light-guiding capillary tubing. FMDs were positioned at a depth of 2.5mm within the cerebrum of male rats with fluoroptic temperature probes placed within 1mm of the FMD tip. Irradiation (without fluid infusion) was conducted at laser powers of 0 (sham), 100, 200, 500, or 750mW. Evans blue-serum albumin conjugated complex solution (EBA) and laser energy co-delivery were performed in a second set of preliminary experiments. Results Maximum, steady-state temperatures of 38.7 +/- 1.6 and 42.0 +/- 0.9 degrees C were measured for the 100 and 200mW experimental groups, respectively. Histological investigation demonstrated needle insertion damage alone for sham and 100mW irradiations. Photothermal damage was detected at 200mW, although observable thermal damage was limited to a small penumbra of cerebral cortical microcavitation and necrosis that immediately surrounded the region of FMD insertion. Co-delivery of EBA and laser energy presented increased volumetric dispersal relative to infusion-only controls. Conclusion Fluoroptic temperature sensing and histopathological assessments demonstrated that a laser power of 100mW results in sub-lethal brain hyperthermia, and the optimum, sub-lethal target energy range is likely 100200mW. The preliminary FMDCED experiments confirmed the feasibility of augmenting fluid dispersal using slight photothermal heat generation, demonstrating the FMD's potential as a way to increase the efficacy of CED in treating MG. Lasers Surg. Med. 45: 167174, 2013. (c) 2013 Wiley Periodicals, Inc.