Photoradiation therapy: current status and applications in the treatment of brain tumors.

Photoradiation therapy is achieved when a photosensitizing drug is activated by light to form products that are lethal to tumor cells. The most commonly used drug is hematoporphyrin derivative, which is preferentially taken up and retained by malignant tissue. Photoactivation is usually produced by using a dye laser tuned at 630 nm (red light). The primary mechanism of neoplastic cell damage in photoradiation therapy involves the production of free radicals formed during illumination of hematoporphyrin derivative by light of this wavelength. The treatment would seem to damage first the tumor cell membrane, then the cytoplasmic inclusions, and finally the nucleus. Photoradiation therapy has been quite effective in the treatment of superficial malignancies, especially in skin, breast, eye, bladder, bronchus, and stomach. Experience with brain tumors is still limited. Important unresolved problems in the application of photoradiation therapy to gliomas include relative uptake of hematoporphyrin derivative into the tumor, limited light penetration of the tissue, local heating, and damage induced in normal brain by photoradiation therapy.