Photofrin photodynamic therapy can significantly deplete or preserve oxygenation in human basal cell carcinomas during treatment, depending on fluence rate

At high fluence rates in animal models, photodynamic therapy (PDT) can phot ochemically deplete ambient tumor oxygen through the generation of singlet oxygen, causing acute hypoxia and limiting treatment effectiveness. We repo rt that standard clinical treatment conditions (1 mg/kg Photofrin, light at 630 nm and 150 mW/cm(2)), which are highly effective for treating human ba sal cell carcinomas, significantly diminished tumor oxygen levels during in itial light delivery in a majority of carcinomas. Oxygen depletion could be found during at least 40% of the total light dose, hut tumors appeared wel l oxygenated toward the end of treatment. In contrast, initial light delive ry at a lower fluence rate of 30 mW/cm(2) increased tumor oxygenation in a majority of carcinomas. Laser treatment caused an intensity- and treatment time-dependent increase in tumor temperature. The data suggest that high fl uence rate treatment, although effective, may be inefficient.