Optical dosimetry in photodynamic therapy

The diffusion approximation for the radiant flux distribution in a tissue layer has been applied to optical dosimetry in photodynamic therapy of malignant tumors. The model assumes that tumor eradication requires a minimum absorbed energy by the localized photosensitizer, taken as 0.19 J/cm3 for hematoporphyrin derivative (HPD) at 630 nm. The analysis leads to the required incident irradiance for front surface illumination as a function of the tumor depth, the optical penetration depth of the tumor, and the concentration of localized sensitizer. The effect of HPD photobleaching on the required light dose and drug dose levels is considered. The results are given in tabular form for typical clinical applications.