Fractionated Illumination for Oesophageal ALA-PDT: Effect on Blood Flow and PpIX Formation

. The effect of fractionating the 633 nm illumination of 5-aminolaevulinic (ALA)-based photodynamic therapy (PDT) of the normal rat oesophagus was studied. Fractionation of the illumination could enhance the PDT effect in two ways: (a) delay of the vascular shutdown or relaxation of the vasoconstriction induced by ALA-PDT and (b) use of newly formed protoporphyrin IX (PpIX), produced during the dark interval. Forty rats were randomly allocated to two groups of 20 animals each. To study vascular effects, in group 1 illumination with 633 nm (100 mW/cm) was performed at 3 h after oral ALA administration (200 mg/kg) either continuously with 20 J/cm diffuser length (n=5) or fractionated 2×10 J/cm with a 150 s interval (n=5), five animals served as controls. Blood flow was measured with a laser Doppler flowmeter. To study the effect of renewed PpIX forming, animals in group 2 were illuminated continuously at 3 h after ALA with 20 J/cm (n=5) or 40 J/cm (n=5) or fractionated 2×20 J/cm with a 3 h interval (n=5), five animals served as controls. In all animals the in vivo fluence rate and PpIX fluorescence were measured during illuminations and animals were killed at 48 h after PDT.