Exploration of Spectral Online Monitoring (SOM) Concepts for Interstitial PDT and Direct Light Therapy (DLT) on Inhomogeneous Tissue Phantoms

Photodynamic Therapy (PDT) has proven to provide unprecedented treatment results for many patients. However, similar approaches not requiring accumulation of a photosensitizer in the target tissue should be explored as new treatment options for diseases not susceptible to PDT. Direct Light Therapy (DLT) will be explored as a treatment option for tumors that do not exhibit tumor-selective accumulation of a photosensitizer. DLT relies on direct optical excitation of intracellular oxygen to singlet oxygen at 1267 nm wavelength to induce phototoxic effects in tumor cells. Dosimetry and monitoring concepts for DLT were examined. Spectral online monitoring (SOM) established for interstitial PDT (iPDT) between cylindrical light diffusers was quantitatively investigated on inhomogeneous optical phantoms at 635 nm and 1267 nm wavelength. For both wavelengths, SOM results can be quantitatively explained using a simple model based on light diffusion theory. This paves the way for transferring results from iPDT to DLT.