Photodynamic therapy (PDT) is an established concept in the treatment of both cancerous and non-cancerous tumors, and it has become an approved treatment method for many other kinds of diseases. PDT requires the combination of a photosensitizing drug, activation light source for a photosensitizer, and molecular oxygen. Optimization of these main components of PDT provides the effective outcome of this therapy. The emerging role of PDT as an effective therapeutic option for esophageal malignancies is, however, challenged by the; (i) limited efficiency of the available light delivery systems and (ii) depletion of molecular oxygen during the treatment.
This work discusses how a currently available light delivery system can be further developed into a higher efficiency of performance. This modified light delivery system can be inserted into the esophagus as a whole, thus avoiding the necessity of any fiber optic coupling techniques. The system is composed of self-contained semiconductor diode lasers that are being cooled by de-ionized (DI) water for efficient removal of heat. This direct water-cooling technique has a higher degree of cooling efficacy, and greatly increases the performance of the lasers.
Tumor destruction due to PDT is mainly governed by the amount of molecular oxygen present in the tumor. Continuous and effective treatment is based on the availability of a constant level of molecular oxygen. Therefore, oxygen is one of the rate-limiting factors in PDT. This rate-limiting factor always makes PDT a lengthy process, as it necessitates interruption in treatment by several intervals, in order to restore the depleted oxygen levels within normal limits. In this work, we propose microwave (MW) heating technique as a mechanism to elevate the local tissue temperature for oxygen enhancement. Extensive mathematical modeling is presented to show the level of microwave heating utilization optimizing the PDT application within safety margins. The tumor is represented by a porous medium of two constituents in order to represent the growth stages of a tumor. The same tumor modeling approach is used to develop a model that calculates the penetration depth of different optical wavelengths in a given tissue medium, with and without photosensitizing agents. Molecular oxygen diffusion in the capillary bed has also been investigated with a similar modeling approach.
Monitoring molecular oxygen level in the PDT application area, with a provision of guidance to manipulate the oxygen enhancement system and the light delivery system, will make PDT a more effective treatment compared to present systems. The design of such a system is a challenging task, as the system should fit into the esophagus together with the light delivery system which is sensitive and specific to oxygen. In addition, the oxygen detection system should not be affected by the main light source used for the activation of the photosensitizer. This is achieved by an optical reflective oxygen detection system designed with a monochromatic light source that does not affect the photosensitizer. Therefore, the oxygen detection system is specific enough to count only oxygen.
Overall, this work integrates designs and models to increase the effectiveness of the light source, and to optimize the oxygen level with an additional element of continuous monitoring. The result is a highly efficient, smart, and portable light delivery system to be used in PDT of esophageal carcinoma.