Light is administered during
photodynamic therapy (PDT) for an extended period of time at a plurality of sites distributed within the abnormal tissue of a tumor. A
clinical study has shown that a substantially greater volume of abnormal tissue in a tumor is destroyed by the extended administration of
light therapy from a plurality of probes than would have been expected based upon the teaching of the prior art. In this process, a plurality of light emitting optical fibers or probes are deployed in a spaced-apart array. After a photoreactive agent is absorbed by the abnormal tissue, the
light therapy is administered for at least three hours. The greater volume of
necrosis in the tumor is achieved due to one or more concomitant effects, including: the
inflammation of damaged abnormal tissue and
resultant immunological response of the patient's body; the
diffusion and circulation of activated photoreactive agent outside the expected
fluence zone, which is believed to destroy the abnormal tissue; a retrograde
thrombosis or
vascular occlusion outside of the expected
fluence zone; and, the collapse of the vascular
system that provides oxygenated blood to portions of the tumor outside the expected
fluence zone. In addition, is possible that
molecular oxygen diffusing and circulating into the expected fluence zone is converted to
singlet oxygen during the extended
light therapy, causing a gradient of hypoxia and anoxia that destroys the abnormal tissue outside the expected fluence zone.