Photodynamic therapy (PDT) for actinic keratosis (AK) and certain non-melanoma skin cancers (NMSC) is performed with either blue light (415nm Lamp), red light (630nm LED Lamps) or with sunlight. The differences in PDT efficacy can be high when using the latter broad-spectrum activation of PpIX. The purpose of this work was to establish a predictive treatment plan approach to daylight PDT which incorporated both local weather forecast information as well as prediction of wavelength-depth dependence upon the efficacy. The concept of PpIX-weighted light fluence is now well established as a way to compare effective light doses from daylight PDT to traditional lamp PDT, but there is limited work to date considering the effects of tissue optical properties or the dynamic distribution of PpIX at depths into the tissue. Using a Monte Carlo model of light fluence in a multi-layer skin geometry we estimate the effective fluence at depth in tissue. The result of these simulations in combination with a model for PpIX production and photobleaching at a range of depths are used to generate lookup tables for the time needed to reach a specific photodynamic dose at a predicted lesion thickness. These tables are then used as the foundation of a web-based application that will better inform the dermatology team of light dosing options. GPS-derived location is used to retrieve forecasted and historical weather patterns automatically, and used as an additional input to further refine prescribed dosing of daylight-PDT. The application is currently being tested in conjunction with fluorescence dosimetry, as a method to verify and alleviate clinical variation in lesion clearing from daylight PDT.
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.
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