Characteristics of PDT performed very shortly after sensitizer injection

Abstract
Clinical PDT is done a few days after injection of the photosensitizer in order to enhance specificity. In animal experiments, however, a strong response is often the principal goal ; this is expected to occur if the time delay between injection and irradiation (td) is short. We have defined criteria to assess the strength of photodynamic lesions produced in healthy tissue (rat ears) and examined its dependence on td and on dose fractionation. It is found that, starting from the shortest experimentally accessible value of td (10 min), the lesion decreases monotonously and that split light delivery (two portions separated by a 7 min interval) enhances the lesion.