Aspectos ópticos e histopatológicos do uso combinado de técnicas cirúrgicas com terapia fotodinâmica

Abstract

Photodynamic therapy (PDT) is an alternative technique for treatment of tumors and other lesions. It results from the combination of three factors: a photosensitizer (PS), molecular oxygen and light. This combination triggers photochemical reactions that result in the destruction of cells and their neighborhoods. Because the FS presents preferential retention in tumors, its effect becomes localized, selectively destroying the tumor parenchyma and stroma only. However, the penetration of light during PDT is limited due to attenuation of the possible excitation wavelengths by the biological tissue itself. Thus, the depth of treatment is not sufficient to ensure the treatment of extensive lesions. To overcome this difficulty, one strategy is to surgically remove the bulk of the lesion, and then applying the PDT on the surgical bed. However, it is unknown how the alterations caused by surgical techniques (bleeding, coagulation, inflammatory processes, etc.) influence the optical properties of biological tissues as to compromise a subsequent PDT protocol. This work aims to study the influence of using surgical techniques prior to a PDT protocol in an animal model. It was applied four surgical tools (electrocautery, ultrasonic scalpel, long-pulsed Er:YAG laser and ultrashort-pulsed Ti: Sapphire laser) in order to verify the most recommended for a surgery + PDT combined protocol, using Photogem ® as the photosensitizer. Surface and subsurface changes were performed to simulate the remaining tissue properties treated with such techniques. The order of application between photosensitization and surgery was one of the study variables. In vivo fluorescence spectroscopy, confocal fluorescence microscopy of the necrotic tissue (ex vivo) and histopathology were used as analysis techniques of the tissue response. The analysis of ex vivo necrosis fluorescence made possible to assess the damage to biological tissues, supporting the histopathological analysis. Analyzing the depth of necrosis was important to confirm the generation of photodynamic effect in tissues previously modified by the use of surgery. Testing a surgical excision protocol, the same success was obtained. Through in vivo fluorescence it was possible to detect the concentration of the PS in all steps of the protocols. A hypothesis of increased electrical conductivity of photosensitized tissue is proposed to explain the decrease in thermal damage observed during excision. Finally, the full feasibility of the combination between surgery and PDT was verified, with space to suggest guidelines for the implementation of future protocols involving combined use of the studied techniques.