Light Fluence Rate and Tissue Oxygenation (S O ) Distributions Within the Thoracic Cavity of Patients Receiving Intraoperative Photodynamic Therapy for Malignant Pleural Mesothelioma

The distributions of light and tissue oxygenation (S O ) within the chest cavity were determined for 15 subjects undergoing macroscopic complete resection followed by intraoperative photodynamic therapy (PDT) as part of a clinical trial for the treatment of malignant pleural mesothelioma (MPM). Over the course of light delivery, detectors at each of eight different sites recorded exposure to variable fluence rate. Nevertheless, the treatment-averaged fluence rate was similar among sites, ranging from a median of 40-61 mW cm during periods of light exposure to a detector. S O at each tissue site varied by subject, but posterior mediastinum and posterior sulcus were the most consistently well oxygenated (median S O >90%; interquartile ranges ~85-95%). PDT effect on S O was characterized as the S O ratio (post-PDT S O /pre-PDT S O ). High S O pre-PDT was significantly associated with oxygen depletion (S O ratio < 1), although the extent of oxygen depletion was mild (median S O ratio of 0.8). Overall, PDT of the thoracic cavity resulted in moderate treatment-averaged fluence rate that was consistent among treated tissue sites, despite instantaneous exposure to high fluence rate. Mild oxygen depletion after PDT was experienced at tissue sites with high pre-PDT S O , which may suggest the presence of a treatment effect.