Measuring the absorbed dose in photodynamic therapy

Abstract

The absorbed dose in photodynamic therapy is proportional to the energy fluence of the irradiating light and the concentration of the photosensitizer, such as dihematoporphyrin ether (DHE). An instrument has been devised to measure the energy fluence rate, based on an isotropic fiberoptic probe coupled to a photodiode. The concentration of DHE is measured either by chemical extraction from a specimen followed by spectrofluorimetry, or by an in vivo measurement of the energy fluence rate of the 690 nm fluorescence emission when excited by either violet (410 nm) from a krypton ion laser, or red (630-633 nm) light from either an argon-dye laser or a helium-neon laser. The fluorescence is detected by a photomultiplier tube after narrowband filtering and a dichroic mirror that separates the exciting and the emitted light. A circuit is provided to ratio the fluorescence signal to the signal from the exciting light. A similar ratioing in vivo fluorometer with background subtraction, has been used for localization of tumors.The absorbed dose in photodynamic therapy is proportional to the energy fluence of the irradiating light and the concentration of the photosensitizer, such as dihematoporphyrin ether (DHE). An instrument has been devised to measure the energy fluence rate, based on an isotropic fiberoptic probe coupled to a photodiode. The concentration of DHE is measured either by chemical extraction from a specimen followed by spectrofluorimetry, or by an in vivo measurement of the energy fluence rate of the 690 nm fluorescence emission when excited by either violet (410 nm) from a krypton ion laser, or red (630-633 nm) light from either an argon-dye laser or a helium-neon laser. The fluorescence is detected by a photomultiplier tube after narrowband filtering and a dichroic mirror that separates the exciting and the emitted light. A circuit is provided to ratio the fluorescence signal to the signal from the exciting light. A similar ratioing in vivo fluorometer with background subtraction, has been used for localizatio...