Modeling PpIX-effective fluence rate in tissue for multiple light sources used in photodynamic therapy of skin (Conference Presentation)

In recent years, numerous publications have documented the growing consensus among dermatologists for daylight-photodynamic therapy (dPDT) treatment of Actinic Kerasotis (AK), with additional evidence supporting treatment of certain non-melanoma skin cancers (NMSC). While these publications aim to address the minimum effective surface-irradiance required for successful clearance, our current work investigates how the tissue optical properties influence the fluence rate within tissue. While it is known red and blue light will have drastically different attenuation profiles in tissue, it is harder to quantify this for broad-spectrum light sources. Our model aims to expand the current PpIX-weighted irradiance metric by incorporating a clinically relevant depth distribution factor. Using a 7-layer skin model, Monte Carlo simulations of optical photons ranging from 350nm – 900nm provide insight into the potential depth of activation of the photosensitizer. Additionally, these models can be applied to known light spectra for both narrow-band conventional treatments (415nm, 633nm), as well as for the Sun and other white light sources (CFL, Halogen). Using this model, we show even when the effective surface-irradiance of the Sun is 4x a halogen light source, the effective fluence within the top 3mm of tissue is generally equivalent, due to the higher proportion of UV-blue light in Sun spectrum which is highly attenuated within the first 50m. We plan to use this model to inform which light source or light combinations would be most appropriate for specific lesion morphologies.