Interstitial Photodynamic Therapy

Photodynamic therapy (PDT) is a treatment modality under development and evaluation, mainly for treatment of malignant tumours. Until now, the treatment has mainly been useful for relatively thin lesions, since the light cannot penetrate deep into tissue. The penetration is limited to approximately 3 mm. In Lund, we are presently developing a system for multiple optical fibre interstitial light delivery for PDT and thermotherapy. An interesting feature with this system is the possibility to monitor light transport through the treated tissue, by using one fibre as emitter and the rest as receivers. This gives us an interesting possibility to monitor the light fluence rate during the treatment. On-line dosimetry is thus possible. It is also possible to dope the fibre-ends with a rare-earth metal. These atoms can provide fluorescence signals that depend on the temperature. It is thus possible to measure the tissue temperature using the same fibres.

The aim of the project is to define the dosimetry challenges necessary to address in the development of multifibre interstitial PDT and exemplify with a solution for a simple case that you define yourselves. 

The intention is that the project should include the following:

• You are supposed to briefly study the field of photodynamic therapy and interstitial PDT. You should also make yourselves familiar with the field of thermotherapy. Identify how far the techniques have been developed and accepted as clinical tools. This background should be included in the introduction of the report. Make sure to cite appropriate literature. 
• It may be possible that you can visit a PDT procedure at the oncology clinic at Lund University Hospital. Please contact the course leader to try to arrange such a visit. 
• You should identify and describe the different challenges to overcome in developing a dosimetry strategy for interstitial photodynamic treatments. Discuss how to handle the light fluence, photosensitizer and oxygen concentrations. Also identify the most appropriate tools necessary and discuss the advantages and limitations with these. Which alternatives exist in terms of photosensitizer and which one(s) is(are) best suited for IPDT? These are broad questions at the research edge, meaning that the ultimate answer is presently not fully available.
• Discuss the influences of treatment geometry, choice of fibre tips and optical properties on the results with the algorithms chosen.
• You should measure the optical properties of tissues of interest for the project at the wavelengths of interest (during the laboratory exercises). Optical properties of skin are difficult to measure, and could if necessary instead be found in the literature.
• You should calculate the light distribution for the wavelength of interest and calculate the treatment volume for a simple case defined by yourselves (during the computer exercises and by yourselves).
• You should calculate the temperature distribution following such a treatment (during the computer exercise or by yourself).

Suggested key-words: PDT, interstitial, thermotherapy, tissue optics