The role of light-emitting diodes for photodynamic therapy of brain tumors

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The development of more effective light sources for Photodynamic Therapy (PDT) of brain tumors would be of benefit for both research and clinical application. In this study, the use of light‐emitting diode arrays for PDT of brain tumors with Photofrin® porfimer sodium was investigated. An inflatable balloon device with an LED tip was constructed. These light‐emitting diodes (LED’s) are based on the new semiconductor Aluminum Gallium Arsenide (AlGaAs). 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 to the absorption spectrum of Photofrin®. This analysis showed that of 27.5% of the LED light emission is absorbed by Photofrin® as compared to a 630 nm monochromatic laser light source. Thus, in order to achieve an energy light dose equivalent to a laser light source, the LED light output has to be increased by a factor of 3.63. This need for additional energy is the difference between a 630 nm and 677 nm absorption of Photofrin®. Using the LED probe and the Laser balloon adapter, a comparison of brainstem 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 (MTD) was 1.6 mg/kg and 100 J/cm2 of light energy (laser or LED). In addition, LED light was able to decrease glioma cell growth in vitro by 50%. This study concludes that LED’s are a suitable light source for PDT of brain tumors with Photofrin®.