Light sources, drugs, and dosimetry

This chapter will address the technical and physical aspects of the light sources, delivery devices, and photosensitizers used in ENT photodynamic therapy (PDT). Effective delivery of treatment light to the target tissue requires appropriate matching of the light source to the tissue, the sensitizer, and the delivery device. Lasers, light-emitting diodes (LEDs), and lamps are three main conventional categories of light sources used for PDT applications. Tumor location, photosensitizer, and optical dose are determining factors for the choice of the light source for PDT. Head and neck cases present a particular challenge, as the geometry is often minimally accessible to external optical fibers. The delivery device, typically an optical fiber with a directional or diffusing termination, must be chosen to match the target area and the surrounding geometry. Tissue optics also plays a critical role in the distribution of treatment light in tissue. Scattering is the dominant mechanism of light attenuation in tissue, except in highly pigmented tissues and short wavelengths, where absorption is the dominant attenuation process. In this chapter, we summarize the basic physics of drugs, and light sources, and describe the methods available to assess the dose delivered to the patient.