Photodynamic Therapy of Tumors: Definition of PDT Dose and Response

Abstract

The PDT dose at any point in tissue can be generally defined as the integral of the Photofrin II concentration over the time integrated space irradiance at that point. We know the dependence of Photofrin II concentration (i.e. photobleaching) as a function of the incident Joules/cm² for a thin superficial layer of tissue. If the space irradiance is also available as a function of the incident light for this geometry we can express the photobleaching of the Photofrin II as a function of the time integrated space irradiance in this layer (we assume that the space irradiance is constant in this thin layer). At this point knowledge of the space irradiance as a function of the incident flux for other simple geometries allows us to determine the PDT dose within the tissue for the clinically interesting cases of an implanted cylindrical source, a water filled bladder with a spherically isotropic source at the center, an implanted spherical source and the case of a uniform surface illumination.