Necrosis Depth and Photodynamic Threshold Dose with Redaporfin-PDT

Predicting the extent of necrosis in photodynamic therapy (PDT) is critical to ensure that the whole tumor is treated but vital structures, such as major blood vessels in the vicinity of the tumor, are spared. The models developed for clinical planning rely on empirical parameters that change with the nature of the photosensitizer and the target tissue. This work presents an in vivo study of the necrosis in the livers of rats due to PDT with a bacteriochlorin photosensitizer named redaporfin using both frontal illumination and interstitial illumination. Various doses of light at 750 nm were delivered 15 min postintravenous administration of redaporfin. Sharp boundaries between necrotic and healthy tissues were found. Frontal illumination allowed for the determination of the photodynamic threshold dose-1.5 × 10¹⁹  photons cm^-3 -which means that the regions of the tissues exposed to more than 11 mm of ROS evolved to necrosis. Interstitial illumination produced a necrotic radius of 0.7 cm for a light dose of 100 J cm^-1 and a redaporfin dose of 0.75 mg kg^-1 . The experimental data obtained can be used to inform and improve clinical planning with frontal and interstitial illumination protocols.