Long-pulse dye laser for photodynamic therapy: Investigations in vitro and in vivo

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Abstract
Background and Objective Continuous wave lasers or incoherent lamps are used effectively for photodynamic therapy (PDT). As the mechanism of action of pulsed lasers in PDT is not known, we investigated the efficacy of PDT with 5‐aminolevulinic acid (ALA) using a long‐pulse (1.5 ms) tunable flashlamp‐pumped pulsed dye laser (LPDL) in vitro and in vivo. Study Design/Materials and Methods HaCaT human keratinocytes were incubated with ALA (3 mmol/l) and irradiated (0–50 J/cm2) using the LPDL at 585 nm, 595 nm, or 600 nm vs. an incoherent light source (580–740 nm). Topical ALA‐PDT was performed on 24 patients with actinic keratoses (AK) on the head (n = 200) after incubation with a 20% ALA emulsion and irradiation by either an incoherent light source (160 mW/cm2, 60–160 J/cm2) or the LPDL (585 nm, 18 J/cm2). Results Maximal cytotoxic effects in vitro were achieved using the LPDL at 585 nm or the incoherent lamp (50 J/cm2). Sodium azide, a quencher of singlet oxygen, significantly reduced cell killing, suggesting that the cytotoxic effects are mainly mediated by singlet oxygen. This is supported by an increase of lipid peroxides as determined by malondialdehyde after adding D2O. Complete remission was achieved in 79% of 100 AK treated by ALA and the LPDL and in 84% of 100 AK treated by ALA and the incoherent lamp. Pain during light treatment was significantly reduced by using the LPDL. Control lesions (LPDL without ALA) did not clear. Conclusion These results show the in vitro and in vivo efficacy of ALA‐PDT using a pulsed light source mediated by singlet oxygen. Lasers Surg. Med. 25:51–59, 1999.

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