Makoto KIMURA^1,2, Kasumi KASHIKURA¹, Satomi YOKOI¹, Yumiko KOIWA¹, Yoshikazu TOKUOKA^1,,* and Norimichi KAWASHIMA^1,3

¹Faculty of Engineering, Toin University of Yokohama, 1614 Kurogane-cho, Aoba-ku, Yokohama 225-8502, Japan
²Ushio Inc, 2-6-1 Asahi Tokai-Building 20F, Otemachi, Chiyoda-ku, Tokyo 150-0021, Japan
³Biomedical Engineering Center, Toin University of Yokohama, 1614 Kurogane-cho, Aoba-ku, Yokohama 225-8502, Japan

(Received September 27, 2004; Accepted March 11, 2005; Revised March 2, 2005)

We determined photodynamic therapy (PDT) efficacy using a flash wave (FW) and a continuous wave (CW) light, of which the fluence rate was 70 μW/cm², for murine thymic lymphoma cells (EL-4) cultivated in vitro. The irradiation frequency and the pulse width of the FW light were in the range of 1–32 Hz and less than one millisecond, respectively. 5-Aminolevulinic acid-induced protoporphyrin IX (ALA-PpIX) was used as a photosensitizer. When EL-4 with ALA administration was irradiated by the light for 4 h (irradiation fluence: 1.0 J/cm²), the survival rate of EL-4 by the FW light was lower than that by the CW light, except for the FW light with irradiation frequency of 32 Hz, and decreased gradually with decreasing irradiation frequency. Moreover, the FW light, especially at lower irradiation frequency, was superior to the CW light for the generation of singlet oxygen in an aqueous PpIX solution. Therefore, the higher PDT efficacy for EL-4 of the FW light would be caused by the greater generation of singlet oxygen in the cells.

Key words: photodynamic therapy, xenon lamps, flash wave light, continuous wave light, 5-aminolevulinic acid, protoporphyrin IX, oxygenation

^*To whom correspondence should be addressed. E-mail address: tokuoka@cc.toin.ac.jp