Light-emitting diodes as a light source for intraoperative photodynamic therapy

THE DEVELOPMENT OF more cost-effective light sources for photodynamic therapy of brain tumors would be of benefit for both research and clinical applications. In this study, the use of light-emitting diode arrays for photodynamic therapy of brain tumors with Photofrin porfimer sodium was investigated. An inflatable balloon device with a light-emitting diode (LED) tip was constructed. These LEDs are based on the new semiconductor aluminum gallium arsenide. They can emit broad-spectrum red light at high power levels with a peak wavelength of 677 nm and a bandwidth of 25 nm. The balloon was inflated with 0.1% intralipid, which served as a light-scattering medium. Measurements of light flux at several points showed a high degree of light dispersion. The spectral emission of this probe was then compared with the absorption spectrum of Photofrin. This analysis showed that the light absorbed by Photofrin with the use of the LED source was 27.5% of that absorbed with the use of the monochromatic 630-nm light. Thus, to achieve an energy light dose equivalent to that of a laser light source, the LED light output must he increased by a factor of 3.63. This need for additional energy is the difference between a 630- and 677-nm absorption of Photofrin. Using the LED probe and the laser balloon adapter, a comparison of brain stem toxicity in canines was conducted. LED and laser light showed the same signs of toxicity at equivalent light energy and Photofrin doses. The maximal tolerated dose of Photofrin was 1.6 mg/kg, using 100 J/cm(2) of light energy administered by laser or LED. This study concludes that LEDs are a suitable light source for photodynamic therapy of brain tumors with Photofrin. In addition, LEDs have the potential to be highly efficient light sources for second-generation photosensitizers with absorption wavelengths closer to the LED peak emission.