Portable Measurement of Protoporphyrin IX in the Skin

Overview

Photodynamic therapy (PDT) is increasingly used to treat superficial skin lesions, such as actinic keratosis (AK) and non-melanoma skin cancers, and has been demonstrated to be an effective and safe alternative to surgery. It is performed by applying a photosensitizing pro-drug, amino -levulinic acid (ALA) and then allowing the conversion to the metabolite Protoporphyrin IX (PpIX). While attempts to measure the concentration of this drug in the skin have been performed before, there remains limited research on an individuals' baseline level of PpIX which could lead to the customization of PDT. With the development of a new handheld, smart phone-associated device to measure red fluoresce intensity of PpIX, this measurement is now feasible. This is an observational single center quantitative study in which the investigators will take measurements of red fluoresce intensity of PpIX at various locations. This will then be correlated with the individuals age, oral temperature, diet, and skin type. The investigators hypothesize that the levels of PpIX will depend on all of these factors, including anatomical location. All data will be collected into the data collection form and then analyzed. The investigators will assess for how anatomical location, skin pigmentation, oral temperature, and other factors influence PpIX levels. Fitzpatrick skin type will be assessed by the provider to assess skin pigmentation. All of these factors will be correlated to the PpIX levels in 5 anatomical locations (forehead, cheeks, forearms, hands, and bald scalp where applicable) to determine which factors most greatly influence the red fluoresce intensity of PpIX.

Photodynamic Therapy (PDT) has gained popularity as an effective, non-scarring treatment for thin, non-hyperkeratotic actinic keratoses (AKs). Similar to the topical agents 5-fluorouracil and imiquimod, PDT is particularly useful when utilized as a field-directed therapy for the treatment of areas with multiple AKs and extensive sun damage. PDT consists of two steps: 1) the topical application of a photosensitizer agent aminolevulinic acid (ALA), which is preferentially converted to the photosensitive protoporphyrin IX (PpIX) in precancerous and neoplastic cells, and 2) controlled exposure to a visible wavelength light source. Current methodologies utilize a "one-size-fits-all" approach with regard to duration of incubation with photosensitizing agents and illumination. Moreover, patients frequently experience pain after long PDT prodrug incubation. Better characterization of photosensitization in PDT can help tailor incubation and overall treatment time to minimize treatment duration and discomfort while maximizing clearance of the target lesions. The direct measurement of PpIX is a promising, yet rarely performed test that may help determine the appropriate PDT treatment time, the need for re-treatment or adjuvant therapy, and potential efficacy of treatment. Point-probe measurements have shown extreme heterogeneity between PpIX levels in different patients and among different lesions in the same patient. However, these point-probe measurements are unable to account for the variance in PpIX production in different parts of the skin because of their relatively limited field of view. The recent development of a low-cost, smart phone-based, wide-field fluorescence dosimetry imaging system to map PpIX levels onto a 2D image allows for handheld, real-time analysis of PpIX levels in human skin. Initial unpublished clinical results have shown its utility in human subjects. However, a more extensive characterization of the factors that influence baseline in PpIX has yet to be performed. This study intends to elaborate these inter-and intra-individual variances, including analysis of changes in PpIX concentrations based on anatomical location, age, diet, temperature, pigmentation, and previous skin damage.