Light dosimetryin vivo
- 1 May 1997
- journal article
- review article
- Published by IOP Publishing in Physics in Medicine & Biology
- Vol. 42 (5) , 763-787
- https://doi.org/10.1088/0031-9155/42/5/003
Abstract
This paper starts with definitions of radiance, fluence (rate) and other quantities that are important with regard to in vivo light dosimetry. The light distribution in mammalian tissues can be estimated from model calculations using measured optical properties or from direct measurements of fluence rate using a suitable detector. A historical introduction is therefore followed by a brief discussion of tissue optical properties and of calculations using diffusion theory, the -approximation or Monte Carlo simulations. In particular the form of the scattering function is considered in relation to the fluence rate close to the tissue boundary, where light is incident. Non-invasive measurements of optical properties yield the absorption coefficient and , where is the scattering coefficient and g is the mean cosine of the scattering angle. An important question is whether this combination is sufficient, or whether g itself must be known. It appears that for strongly forward scattering, as in mammalian tissues, rather detailed knowledge of the scattering function is needed to reliably calculate the fluence rate close to the surface. Deeper in the tissue is sufficient. The construction, calibration and use of fibre-optic probes for measurements of fluence rate in tissues or optical phantoms is discussed. At present, minimally invasive absolute fluence (rate) measurements seem to be possible with an accuracy of 10 - 20%. Examples are given of in vivo measurements in animal experiments and in humans during clinical treatments. Measurements in mammalian tissues, plant leaves and marine sediments are compared and similarities and differences pointed out. Most in vivo light fluence rate measurements have been concerned with photodynamic therapy (PDT). Optical properties of the same normal tissue may differ between patients. Tumours of the same histological type may even show different optical properties in a single patient. Treatment-induced changes of optical properties may also occur. Scattered light appears to contribute substantially to the light dose. All these phenomena emphasize the importance of in situ light measurements. Another important dosimetric parameter in PDT is the concentration and distribution of the photosensitizer. Apart from in vivo fluorescence monitoring, the photosensitizer part of in vivo PDT dosimetry is still in its infancy.Keywords
This publication has 95 references indexed in Scilit:
- Quantifying Light and Ultraviolet Radiation in Plant BiologyPhotochemistry and Photobiology, 1996
- Clinical determination of tissue optical properties by endoscopic spatially resolved reflectometryApplied Optics, 1996
- Estimation of the parameters of dye distributions by optical probingPublished by SPIE-Intl Soc Optical Eng ,1995
- Clinical measurements of tissue optical properties in the esophagus and in the oral cavityPublished by SPIE-Intl Soc Optical Eng ,1994
- Method for measuring position-dependent volume reflectionApplied Optics, 1993
- Light delivery systems for adjunctive intraoperative photodynamic therapyLasers in Medical Science, 1993
- OPTICAL PROPERTIES OF EXPERIMENTAL PROSTATE TUMORS in vivoPhotochemistry and Photobiology, 1993
- Optical dosimetry for interstitial photodynamic therapyMedical Physics, 1989
- Refractive index of some mammalian tissues using a fiber optic cladding methodApplied Optics, 1989
- The Use of Lipid Emulsion as an Intravesical Medium to Disperse Light in the Potential Treatment of Bladder TumorsJournal of Urology, 1985