Abstract

The response of human glioma spheroids to repetitive 5-aminolevulinic acid-mediated photodynamic therapy was investigated. In all cases, light fluences were kept below toxic thresholds to simulate conditions typically found at 1-2 cm depths in brain adjacent to tumor. Significant inhibition of spheroid growth was observed following multiple PDT treatments at sub-threshold light fluences. The effect appears to be insensitive to the treatment intervals investigated. In all cases, suppression of growth was observed for the duration of treatment. Low fluence rates appear to be more effective than high fluence rates. No evidence of PDT resistance was found in this investigation.