The photodynamic effect of a pulsed dye laser on human bladder carcinoma cells in vitro.

The photodynamic effect of a pulsed flashlamp pumped dye laser on cultured human bladder carcinoma cells was studied. MGH-U1 cells were incubated for 1 h in dihaematoporphyrin either (DHE) and then exposed to green laser light (504 nm, 20 Hz) for varying laser power densities (50-100 mW/cm2 and exposure times (2-15 s), representing incident pulse energy fluences of 2.5-5 mJ/cm2 and energy densities of 0.1-1.5 J/cm2. The cell survival was measured by clonogenic assay and controls exposed to either laser light alone or DHE in the dark showed no cytotoxicity. Sensitised cells were killed by energy densities of less than 1 J/cm2 (LD90 = 0.54 J/cm2). This demonstrates the probable effectiveness of a pulsed dye laser for photodynamic therapy provided that pulse fluence are below the saturation threshold of the photosensitiser (10 mJ/cm2).