Portable Photonics Optical Detection System for Monitoring Molecular Oxygen and Photosensitizer Concentration in Photodynamic Therapy Milieu

Abstract

Photodynamic therapy (PDT) is an FDA approved, effective, and minimally invasive cancer treatment modality with few side effects. Optimization of the PDT protocol for individual patient requires good therapeutic selectivity and high efficacy. This is possible only by enabling continuous monitoring of treating area of each patient for essential components for PDT. Two most essential components of PDT are photosensitizing agents and molecular oxygen. Currently the PDT is rather a blind process since there are no proper methods to monitor the tumor blood oxygen level and photosensitizer concentration during the treatment. In this paper we present an optical technique to monitor the tumor oxygen level and photosensitizer concentration. The technique investigated in this paper is a reflection optical technique designed with tiny semiconductor lasers and a silicon photodiode. The measurement of blood oxygen level with optical technique is not an uncommon method, but conventional transmission technique cannot be applied to the internal organs such as esophagus, trachea, and intestine. The light used in the monitoring system comes from three semiconductor diode lasers of 630nm, 650 nm and 940 nm wavelengths. Three lasers and the photodiode are mounted on to a small package to be able to imprint on to the balloon catheter that the PDT light delivery system is carrying in case of body cavities. Lasers and the photodiode are powered and controlled by the control box that is connected with a tinny cable. Light sources and respective photodiode output is controlled by the LabVIEW virtual instrumentation. The sequential on and off of light source and respective reflective signal is processed with MATLAB code integrates in the LabVIEW to make automatic calculation of the corresponding light absorption by each chromophore and to show the change in oxygen level and the photosensitizer concentration in the monitoring area. The designed system is capable of monitoring change in oxygen and photosensitizer level in any part of the human body where the tinny package is possible to place.