Comparison of lasers for photodynamic therapy with a phthalocyanine photosensitizer

Three different lasers were compared under the same conditions for their effectiveness at producing photodynamic damage to normal colon following sensitization with aluminium sulphonated phthalocyanine (AlSPc). One laser was an argon ion pumped continuous wave (CW) dye laser and the other two were pulsed at 10 kHz (copper vapour laser pumped dye laser, and 5 Hz (flashlamp pumped dye laser). The CW and 10 kHz laser were equally effective at producing damage. The 5 Hz laser failed to produce a photodynamic effect, although occasionally caused a photomechanical effect when the laser fibre was placed touching the colonic mucosa. Quantitative analysis suggests that the high energy pulses of the flashlamp pumped dye laser saturate AlSPc, so very little of the available energy can be used to produce a photodynamic effect, in contrast to the two other lasers which do not produce saturation conditions.