Choice of optimal wavelength for PDT: the significance of oxygen depletion.
We have investigated the role of tissue oxygenation on light penetration into tissue at different wavelengths. As a field of application we have chosen aminolevulinic acid-photodynamic therapy (ALA-PDT). To calculate efficiency spectra of PDT on human skin one needs to know the excitation spectrum of the photosensitizer of interest and the relative fluence rate as a function of depth in the tissue. We measured the former and computed the latter with an accurate radiative transfer algorithm. In this way we determined the efficiency spectra as functions of depth for different types of basal cell carcinomas (BCC). Our results suggest that ALA-PDT works best for nodular BCC at a wavelength of 630 nm, whereas it works best for pigmented superficial BCC at a wavelength of 390 nm. At 630 nm the light penetration into a tumor depends strongly on the oxygenation of the blood. Below a 2 mm thick, well-oxygenated, nodular BCC, we find the efficiency to be an order of magnitude larger than below a poorly oxygenated tumor. At 390 nm, the light penetration into a tumor does not depend on the oxygenation of the blood.
Nielsen
Kristian P
KP
Department of Physics and Technology, University of Bergen, N-5007 Bergen, Norway. Kristian.Nielsen@ift.uib.no
Juzeniene
Asta
A
Juzenas
Petras
P
Stamnes
Knut
K
Stamnes
Jakob J
JJ
Moan
Johan
J
D000622:Aminolevulinic Acid / Q000627:therapeutic use*; D002280:Basal Cell Carcinoma / Q000188:drug therapy*; D006801:Humans; D008027:Light; D008954:Models, Biological; D010101:Oxygen Consumption / Q000502:physiology*; D010778:Photochemotherapy / Q000379:methods*; D017319:Photosensitizing Agents / Q000627:therapeutic use; D012680:Sensitivity and Specificity; D014466:Ultraviolet Rays
D017319:Photosensitizing Agents; D000622:Aminolevulinic Acid