Fluence rate effects in human glioma spheroids: implications for photodynamic therapy of brain tumors

The effects of fluence rate are investigated in human glioma spheroids incubated in 5-aminolevulinic acid (ALA). It is shown that the response of glioma spheroids to ALA-mediated PDT depends strongly on the rate at which the light dose is delivered. At low doses, lower fluence rates are more effective. For example, at a dose of 50 J/cm(2), near total spheroid kill is observed at fluence rates of as low as 10 mW/cm(2). Below 10 mW/cm(2), however, treatments are not as effective. The fluence rate effect is not as pronounced at higher doses where a favorable response is observed throughout the range of fluence rates investigated The clinical implications of these findings are discussed.