Transient absorption changes in vivo during photodynamic therapy with pulsed-laser light.
High intensity pulsed-laser light can be used to excite absorbing molecules to transient states in large proportions. The laser-induced spectral changes can be characterized by transient changes in light propagation; through the tissue provided the excited states of these molecules have altered absorption spectra. Characterization of these transient changes may then be used to exploit new mechanisms in photosensitization and/or to optimize photobiological effects. In this study, transmittance and reflectance were measured as a function of laser pulse energy, from tissue-simulating media as well as in rat muscle and liver slices, both with and without the photosensitizer benzoporphyrin derivative monoacid (BPD-MA) present. There was a transient decrease in absorption from the photosensitizer at peak pulse irradiance in the range of 100-1000 W cm(-2). The depth of photodynamic treatment-induced tissue necrosis was measured in a subcutaneous prostate cancer model in Copenhagen rats. A comparison between continuous wave irradiation and pulsed irradiation with the same average incident irradiance showed no statistically significant difference in the depth of necrosis at 48 h after irradiation. These results indicate that photosensitizer population-state changes are measurable in tissues and may provide a method for measuring triplet-state properties of photosensitizer in vivo, but for BPD-MA at clinically used concentrations these changes do not significantly affect the depth of photodynamically-induced tissue damage.
Department of Dermatology, Massachusetts General Hospital, Boston 02114, USA.
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D000042:Absorption; D000818:Animals; D003198:Computer Simulation; D004195:Disease Models, Animal; D053685:Laser Therapy; D008297:Male; D009336:Necrosis; D010778:Photochemotherapy / Q000379:methods*; D017319:Photosensitizing Agents / Q000494:pharmacology*; D011166:Porphyrins; D011471:Prostatic Neoplasms / Q000188:drug therapy* / Q000378:metabolism* / Q000473:pathology; D011838:Radiation-Sensitizing Agents; D051381:Rats; D011919:Rats, Inbred Strains
D017319:Photosensitizing Agents; D011166:Porphyrins; D011838:Radiation-Sensitizing Agents; C504224:benzoporphyrin D