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Light delivery and light dosimetry for photodynamic therapy
Authors:Willem M. Star
Affiliation:(1) Department of Clinical Physics, Dr. Daniel den Hoed Cancer Centre, PO Box 5201, 3008 AE Rotterdam, The Netherlands
Abstract:
Photodynamic therapy (PDT) has attracted attention because it was considered to be a selective form of cancer treatment causing minimal damage to normal tissues. This is not exactly true, because the ratio between the photosensitizer concentrations in tumour and surrounding normal tissues is not always much more than one. Nevertheless, tumour destruction by PDT with relatively little damage to normal tissue is possible in many cases. This requires sophisticated light delivery and/or light dosimetry techniques. In this respect the limited penetration of light into biological tissues can sometimes be useful. In this paper a qualitative and sometimes quantitative discussion is given of the physical phenomena determining the energy fluence in a biological tissue. Most important is light scattering, the contribution of which depends on the geometrical conditions. Finite beam surface irradiation, irradiation of hollow organs (bladder) and interstitial irradiation are discussed separately. The emphasis is on light lsquodosersquo and light dose distribution. It is emphasized that PDT dosimetry in general is complicated by photosensitizer distribution (which is usually not known), by photobleaching of the sensitizer, by possible effects of hyperthermia, and by changes in optical properties during and as a result of PDT.
Keywords:Photodynamic therapy  Light delivery  Light dosimetry  Tissue optics  Scattering  Absorption  Diffusor  Dosimetry probe
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