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Red light (approximately 630 nm) is almost universally used in photodynamic therapy (PDT) as it is the most penetrating of the porphyrin excitation wavelengths. For the treatment of superficial (pre)malignant oesophageal lesions however green light might be more efficient than red in destroying this thin lesions. This study aimed to compare several powers and doses of red and green light for photodynamic therapy with 5- aminolevulinic acid (ALA)-induced photosensibilization of the normal rat oesophagus. Sixty rats received 200 mg/kg ALA orally. Ten untreated rats served as controls. In groups of five rats, at three hours after ALA administration the oesophagi were illuminated with red (633 nm) or green (532 nm) light, using a 1 cm cylindric diffuser, which was placed in the center of an inflated balloon catheter. Several treatment schemes were applied: 33 mW/cm diffuser during 250 and 750 seconds (providing 8.3 and 25 J/cm diffuser), 100 mW/cm diffuser during 83 and 250 seconds (providing 8.3 and 25 J/cm diffuser) and 300 mW/cm diffuser during 83 and 250 seconds (providing 25 and 75 J/cm diffuser). During illumination, fluorescence in the oesophagus was measured. The rats were sacrificed at 48 hours after illumination. During illumination, fluorescence declined in a rate that was dependent on the light-power that was used. A higher power resulted in a faster decline of fluorescence intensity. Both the red-light control group the and green-light control group did not show any damage histologically. In the red light group selective epithelial damage was seen most pronounced in the groups treated with 33 mW/cm diffuser. Illumination during 750 seconds however, also resulted in considerable muscle damage. In the green light group in all subgroups less damage was seen. Only illumination with 300 mW/cm diffuser during 250 seconds resulted in good PDT effect in 2 out of 5 rats. In the rat oesophagus, the efficacy of ALA-PDT treatment depends both on wavelength and illumination scheme. In this study best results were obtained using red light, in a power setting of 33 mW/cm diffuser. The optimal light-dose probably lies between 8.3 and 25 J/cm diffuser.
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