Abstract

A new and promising method for localization and treatment of certain forms of cancer is based on the joint action of laser irradiation and a fluorescent photosensitizer. This technique, which is customarily referred to as photoradiation therapy, is currently under development in various institutions and hospitals throughout the world. A nontoxic, photosensitizing dye with fluorescent properties, hematoporphyrin derivative, is first injected systematically. After 2–3 days this dye exhibits a higher retention in the cancerous region than in the surrounding normal tissue. Subsequent irradiation with a proper optical wavelength, mainly red light around 630 nm, results in rapid necrosis of the neoplastic tissue. However, the absorption by skin pigments for this visible light is usually larger, to a greater extent, than that of a Nd:YAG laser output at 1.064 μm. Hence spectroscopic studies including absorption and fluorescence were performed using hematoporphyrin dihydrochloride (Hp.2HCI) dissolved in PBS and ethanol solutions excited by Q-switched Nd:YAG laser output and its second harmonic beam at 532 nm. The visible fluorescence thus observed by Nd:YAG laser irradiation was attributed to the two-photon absorption, although its intensity was ∼10⁻⁴ weaker than that for second harmonic excitation. Survival rate of cultured esophagus cancer cells uptaken Hp.2HCI exhibited a linear decrease with the Nd:YAG laser irradiation time, and this two-photon excited photochemical effect was formed more appreciably for higher dye concentration.

© 1985 Optical Society of America