On the use of light for the characterization and treatment of malignant tumours

Sammanfattning: Some aspects on the use of light for tissue characterization and treatment of malignant tumours are discussed within this thesis. The work presented aims at improving optical techniques for tissue characterization, especially to detect malignant and pre-malignant lesions. A knowledge on the interaction between light and tissue is of utmost importance to understand and improve the various techniques. A relatively thorough discussion on the light propagation in scattering media is given. A commonly used mathematical model, the diffusion approximation of the transport equation, is derived. Moreover, knowledge of the optical properties of tissue, i.e., the absorption and scattering coefficients, the scattering anisotropy, and the refractive index, is needed to use the mathematical models. Various techniques for in vivo measurements of the tissue optical properties are presented. Furthermore, some of these techniques have been developed into prototype equipment to be used for breast cancer detection, as an alternative to the ordinary mammography based on ionizing X-rays. A therapeutic modality, photodynamic therapy (PDT), presently being introduced into clinical practice has also been investigated. This technique relies on the selective uptake of a photosensitizing agent, and the subsequent irradiation using light. The light absorbed by the photosensitizer triggers a photochemical reaction, leading to local cell death. In the work presented here, d-aminolevulinic acid (ALA) induced protoporphyrin IX (PpIX) has been used as a photosensitizer. A randomized Phase III clinical trial has been conducted to compare PDT with cryosurgery for the treatment of basal cell carcinomas of the skin. The influence on the treatment of various parameters have been investigated and are discussed. Laser-induced fluorescence studies were performed to detect and demarcate superficial malignant and pre-malignant lesions. Both the tissue autofluorescence and the characteristic emission of fluorescent tumour markers were employed. Fluorescence was also used to monitor the selective buildup and the photodegradation of the photosensitizer in connection to PDT, using a point-monitoring technique. Two fluorescence imaging systems have also been used to outline skin lesions. Laser-Doppler perfusion imaging is a non-contact optical technique used to monitor the superficial blood perfusion, and was here used to evaluate the healing time following cryosurgery and PDT.