A system for photodynamic therapy (PDT) that provides, in addition to the therapeutic light dose, a method of real-time, intraoperative dosimetry will be assembled and demonstrated. In PDT, a parenterally administered photoactive dye (dihematoporphyrin ether, DHE) localizes in malignant tissue. Subsequent irradiation of the DHE-bearing tissue with light (630 nm) produces, in combination with oxygen, the cytotoxic reaction product, singlet oxygen (102). By monitoring the real-time-resolved 102 fluorescence at 1.27 nm, a signal proportional to the 102 production rate will result, thereby providing dosimetry information.The system to be demonstrated employs a CW-pumped, Q-switched, frequency-doubled YAG laser driving a tunable dye laser emitting 70nanosecond, 630-nanometer wavelength pulses at a 10-KHz rate. In addition to providing realtime dosimetry information, the system also allows for the study of a possible increase in the therapeutic effect due to the generation of the cytotoxic agent 102 in "bursts." To date, the reciprocity of the PDT light dose does not appear to have been thoroughly investigated.Finally, the inherent wavelength agility of a tunable dye laser makes this system useful with new photoactive dyes operating beyond 630 nm.National Cancer Institute (NCI)
