Yoshikazu TOKUOKA¹, Toshiyuki KOSOBE², Makoto KIMURA², Shirou WAKUI¹ and Norimichi KAWASHIMA^1,2

¹Biomedical Engineering Center, Toin University of Yokohama, 1614 Kurogane-cho, Aoba-ku, Yokohama 225-8502, Japan
²Faculty of Engineering, Toin University of Yokohama, 1614 Kurogane-cho, Aoba-ku, Yokohama 225-8502, Japan

(Received September 10, 2002; Accepted December 9, 2002; Revised December 2, 2002)

New metal-halide lamps were developed and their effect on the efficiency of photodynamic therapy (PDT) for cancer cells, murine thymic lymphoma cells (EL-4), was investigated. 5-Aminolevulinic acid-induced protoporphyrin IX was used as a photosensitizer. The metal-halide lamps were made by introducing sodium iodide (Na lamp), lithium iodide (Li lamp), and sodium iodide-lithium iodide mixture (Na–Li lamp) into their discharge tubes. These lamps emitted light in the range of 550 to 750 nm and had specific emission peaks at 580 and 600 nm for the Na lamp, 580, 610, and 680 nm for the Li lamp, and 580, 610, and 675 nm for the Na–Li lamp. Changes in the survival rate of EL-4 with increasing irradiation time indicated that PDT efficiency of the lamps increased in the order Li lamp < Na lamp < Na–Li lamp. We also found that a dark interval during irradiation of the light with the Na–Li lamp enhanced PDT efficiency.

Key words: photodynamic therapy, metal-halide lamp, 5-aminolevulinic acid, cancer, PDT efficiency, wavelength, irradiation fluence, fluence rate, dark interval