Light dosimetry in vivo in interstitial photodynamic therapy of human tumors

摘要

Photodynamic therapy, developed since 1961 with Lipson's studies, is now limited in its clinical applications by the lack of knowledge about light comportment and the action of hematoporphyrin in tissues. Using human tumor models in mice, the intratumoral light flux was measured during an interstitial illumination (cylindrical diffusor 5 mm of length) by an argon dye laser emitting continuously at 630 nm (Spectra-Physics 375 B). The flux measured was captured by a plane-cut fiber (400 $mu@m) linked with an optical power meter (Newport 815). The light decrease in tissue had an exponential shape, and k, the global attenuation coefficient, was easily calculated as well as the depth penetration (1/k). Control measurements were performed in beef muscle, and the k value was very consistent with published data. In small tumors ($LS 2 cm$+3$/), the results presented a good reproducibility for the same histology (ksarcoma $EQ 0.48 $POM 0.08 mm$+$MIN@1$/, kcholangiocarcinoma $EQ 0.67 $POM 0.01 mm$+$MIN@1$/). The intraperitoneal injection of hematoporphyrin derivative (HpD at 10 mg/kg) did not seem to significantly influence the light evolution in tissues compared with control measurements without HpD. The simplicity and the reproducibility of this technique raises hopes of a coming clinical application and a possible comparison between different studies with measurable references.