Abstract

Depending on the geometry and the tissue optical properties, the amount of scattered light may be more than 80% of the total light fluence delivered during PDT. Nevertheless, the "light dose” in Photodynamic Therapy is still often reported in terms of incident light fluence or worse, in terms of the power emitted by the light source. For example, light for PDT in the trachea, bronchi or esophagus may be delivered by means of a cylindrical diffuser and clinical protocols prescribe the "light dose" as mW per cm diffuser length. This does not take into account the diameter of the lumen, which may vary considerably, causing considerable variations in incident fluence rate for the same delivered power. Furthermore, for a given incident fluence and a fixed geometry, intra- and inter-patient variations in optical properties cause variatons in scattered light which cause variations in total fluence if dosimetry is based on incident light alone. A case in point is whole bladder PDT, where it has been found that the total fluence delivered to the bladder wall may vary between 3 and 7 times (mean 4.8 ±1.2) the incident, non-scattered fluence [1], Wherever possible, the light fluence should therefore measured in situ.

© 1998 Optical Society of America