SEQUENCING OF COMBINED HYPERTHERMIA AND PHOTODYNAMIC THERAPY

Photodynamic therapy (PDT) and hyperthermia are two alternative tumor treatment modalities currently being investigated in clinical trials. It has been suggested that, due to the differences in cell-killing mec hanisms, synergetic tumor responses may be achieved if the two modalit ies are combined in appropriate sequences, This hypothesis is tested i n the current study by delivering graded PDT doses during a transient tumor reoxygenation period after a hyperthermia treatment, or deliveri ng graded hyperthermia doses when the tumor becomes acidic and hypoxic after a PDT treatment, The results indicate that the latter combinati on sequence has a profound effect on tumor response. While treating th e tumors with PDT followed by hyperthermia evokes a synergetic tumor r esponse, reversing the sequence results only in an additive effect, Po ssible mechanisms associated with tissue oxygenation are discussed. (C ) 1996 by Radiation Research Society