29th Annual Meeting of the American Society of Photobiology

Downtown Marriot

Chicago, Il.

Translating optical dosimetry to practical bedside PDT protocols

Abstract-
The FDA has approved prescriptions of photosensitizing drug and activating light to be administered to patients receiving PDT (photodynamic therapy). But what is the received dose of drug that accumulates and light that penetrates the tissues at a particular treatment site of a patient? This continuing study documents the amount of drug (Photofrin) that accumulates in esophageal cancer patients based on the in vivo measurement of Photofrin fluorescence using an optical fiber catheter via an endoscope. The study also measures the light penetration in the tissue that varies with the blood perfusion of the treatment site using a two-fiber side-viewing catheter via an endoscope. The results to date in 7 patients (42 tissue sites) show no trend of difference in Photofrin uptake between normal and cancerous sites but a significant variation in the Photofrin accumulation over all sites (standard deviation/mean = 0.327). The optical penetration depth (1/e penetration depth at 630 nm wavelength) was significantly less in blood perfused tumor sites than in normal tissue sites. The light penetration for tumors was about 1/2 that for normal sites (6 tissue sites). The depth of treatment is proportional to the 1/e optical penetration depth for PDT in thick tissues. The conclusion is that optical measurements can serve as a quality control procedure to identify the failure to accumulate sufficient photosensitizer for efficacious PDT and to identify excess blood perfusion that interferes with activating light penetration and limits the depth of treatment.

Keywords: dosimetry, optics, perfusion