Interstitial photodynamic therapy – What we have learned from spectral online monitoring and medical imaging

Applications of photodynamic therapy and diagnosis are widely spread over many medical disciplines [1]. Optical dosimetry calculations that include the estimation of thermal effects [2-3] are inevitable to guarantee a sufficient disease control while at the same time preserving tissue at risk [4]. Optical monitoring in an interstitial setting has turned out to be very elucidating, both regarding the initial state of the tissue to be treated, and regarding therapy-induced changes of the optical properties of the tissue [5-7], beyond the assessment of photobleaching. This information can be utilized immediately in the surgery room, to individualize, monitor and optimize the therapy session, as well as to warrant and optimize patient safety. Furthermore, by combining all available information around a PDT intervention, further insight about the involved processes and mechanisms can be gained [5-6], which can be utilized to develop the therapeutic approach further as a whole. As an example, the quite promising clinical outcome of iPDT treatments on malignant brain tumors will be summarized [7-8] and evaluation concepts based on spectral online monitoring and medical imaging [5-7], before and after the intervention, will be illustrated. iPDT-induced effects, including conversion of hemoglobin, will be discussed in relation to tumor coverage by the illumination volume and the location of recurrences.