IN-VIVO FLUORESCENCE KINETICS AND PHOTODYNAMIC THERAPY USING 5-AMINOLEVULINIC ACID-INDUCED PORPHYRIN - INCREASED DAMAGE AFTER MULTIPLE IRRADIATIONS

The kinetics of fluorescence in tumour (TT) and subcutaneous tissue (S T) and the vascular effects of photodynamic therapy (PDT) were studied using protoporphyrin IX (PpIX), endogenously generated after i.v. adm inistration of 100 and 200 mg kg(-1) 5-aminolaevulinic acid (ALA). The experimental model was a rat skinfold observation chamber containing a thin layer of ST in which a small syngeneic mammary tumour grows in a sheet-like fashion. Maximum TT and ST fluorescence following 200 mg kg(-1) ALA was twice the value after 100 mg kg(-1) ALA, but the initia l increase with time was the same for the two doses in both TT and ST. The fluorescence increase in ST was slower and the maximum fluorescen ce was less and appeared later than in TT. Photodynamic therapy was ap plied using green argon laser light (514.5 nm, 100 J cm(-2)). Three gr oups received a single light treatment at different intervals after ad ministration of 100 or 200 mg kg(-1) ALA. In these groups no correlati on was found between the fluorescence intensities and the vascular dam age following PDT. A fourth group was treated twice and before the sec ond light treatment some fluorescence had reappeared after photobleach ing due to the first treatment. Only with the double light treatment w as lasting TT necrosis achieved, and for the first time with any photo sensitiser in this model this was accomplished without complete ST nec rosis.