THE CLINICAL VALIDATION OF OXYGEN SATURATION IMAGING FOR VISUALIZING THE MODE OF ACTION OF PHOTODYNAMIC THERAPY FOR ESOPHAGEAL CANCER

Aims Photodynamic therapy (PDT) consists of a photosensitizer and specific wavelength laser illumination, and the mode of action of PDT is known as production of reactive oxygen species in cancers cells and vascular shutdown effect. However, it is difficult to confirm the effect of PDT with ordinary endoscopy. Oxygen saturation (OS) imaging (FUJIFILM, Co., Tokyo) is a novel endoscopic technology which can directly measure and visualize the tissue oxygen saturation (StO₂) of the surface of gastrointestinal tract. OS imaging is suspected as an ideal modality in theory for observing the vascular shutdown effect due to PDT. The purpose of this study is to validate the OS imaging for visualization the mode of action of PDT for esophageal cancer.

Methods 13 patients with local recurrence after chemoradiotherapy for esophageal cancer were treated with PDT consisting talaporphin sodium and diode laser, and enrolled. Endoscopic observation using ordinary endoscope and OS imaging were performed before PDT, after illumination of 100 J/cm², after illumination completion and one day after. StO₂ was measured at three points in the lesion using the OS imaging sampling tool for each evaluation.

Results OS imaging showed the extreme change to hypoxic state in accordance with the illuminated area, even though there was the almost invisible change with WLI. The median StO₂ value (%) at tumor lesion was 62 (range: 17–99) before PDT, and significantly decreased immediately after illumination, as follow; 3 (range: 0–57) at 100 J/cm² illumination, 1 (range:0–6) at the completion of PDT and 3 (range: 0–32) at the second day.

Conclusions OS imaging was validated to visualize the changes of StO₂in tumor before and after laser illumination. It can be the ideal imaging modality to observe the mode of action of PDT in clinical.