In vivo determination of tumor optical parameters in esophageal carcinoma

Dose dependence of light cannot be discussed on the basis of dose alone. On a more fundamental scientific level, the propagation of light in tissue depends on optical parameters of treated tumor tissue. In a prospective, nonrandomized study, in vivo optical parameters of esophageal carcinoma were studied.

Nineteen intraoperative measurements of tumor optical parameters in six patients with esophageal carcinoma were performed. After diagnostic work-up and clinical staging, right-sided, posterolateral thoracotomy, and dissection of the esophagus were carried out. The tumor site was exposed and continuous endoluminal irradiation was started during determination of light penetration at the level of the adventitia of the esophagus. The tumors were located exactly between the endoluminal irradiation source and measurement probe in the thoracic cavity. Measurements were performed on tumors having different diameters to show the relationship between tumor diameter, extinction coefficient, and light penetration depth.

The endoluminal incident intensity was 18.5 mW/cm(2). At a tumor diameter of 4, 6, 8, and 9 mm measured intensity of 5.12, 2.28, 0.88 and 0.65 mW/cm(2), an extinction coefficient of 0.321, 0.349, 0.381, and 0.373, as well as penetration depth of 3.21, 2.87, 2.62, and 2. 68 mm, respectively, could be measured. The correlation of tumor optical parameters, tumor diameter, penetration depth, and treatment time were expressed by the relative correction factor for different tumor diameters.

The knowledge of tumor optical properties seems to be necessary to adapt dosimetry to the individual situation and manage optimal results of PDT in esophageal cancer.