THE WAYS TO OPTIMIZE CLINICAL OUTCOMES OF PHOTODYNAMIC THERAPY BY OPTICAL IMAGING TECHNIQUES

Abstract

Background: Photodynamic therapy (PDT) is a modern minimally invasive technique for treatment of a wide range of diseases, including malignancies. One of directions for PDT development is the individualization of exposure modes that can be achieved with effective treatment monitoring. There are a number of approaches employing imaging techniques, the most promising of them being optical ones. Aim: To analyze factors affecting clinical outcomes of PDT in non-melanoma skin tumors, and to evaluate the prospects of optical imaging techniques for PDT planning and monitoring. Materials and methods: We retrospectively analyzed various aspects of the results PDT obtained in 855 patients with non-melanoma skin tumors. PDT was performed with systemic chlorine photosensitizers. As a source of irradiation, the laser at a wavelength of 662 nm was used following exposure modes: mean power density 0.3 W/cm², the laser irradiation dose of 200 J/cm² for basal cancer and 300 J/cm² for squamous cell carcinoma. Clinical evaluation was performed based on tumor response according to RECIST criteria, by the presence or absence of recurrence during long term follow up and by the presence or absence of cosmetic defects. Fluorescence imaging and optical coherence tomography were used as non-invasive imaging techniques. Results: It was found that clinical predictors of treatment failure included tumor recurrence, squamous type of tumor, and advanced exophytic or infiltrative component. Fluorescence imaging showed an association between clinical outcomes of PDT and fluorescence characteristics of the photosensitizer. The best clinical outcomes were achieved in 147 patients with a combination of high contrast fluorescence (FC>1.2) and a high degree of photobleaching of the agent (ΔIt/IN >25%): the number of complete tumor responses was 94% (138 of 147), with recurrence seen in 3 (2%) patients only with the follow up from 6 to 53 month duration. Clinical predictors of PDT cosmetic failures are tumor recurrence and tumor stage above T2. The most vulnerable zones are the outer ear and nose wings; this fact is related to an involvement of the cartilage located directly beneath the thin skin in the photodynamic reaction. This was demonstrated by optical coherence tomography. Conclusion: Presence of clinical predictors of PDT failure justifies correction of light exposure modes that can be optimally implemented with techniques for objective evaluation of the tumor borders, photosensitizer accumulation and photobleaching. Dynamic non-invasive monitoring of PDT procedure with fluorescence imaging and optical coherence tomography seems promising for implementation of an individual approach resulting in optimal oncological and functional outcomes.