Introduction to radiotherapy and standard teletherapy techniques.

Radiation was first discovered in the late 19th century by Wilhelm Roentgen and has since been used extensively to treat a variety of cancers. Over the last century, we have developed an extensive understanding of the physical properties of radiation as well as radiation biology. Technological advances in the last few decades in medical imaging and radiotherapy delivery have led to the development of highly complex radiation delivery systems such as intensity modulated radiotherapy, which can be utilized to conformally treat complex tumor shapes while minimizing radiation dose to the surrounding normal tissue. To completely appreciate the application of radiotherapy for ophthalmic cancers, it is important to have a basic understanding of radiation therapy. In this chapter, we will discuss the fundamentals of radiation and radioactive decay, the mechanism of tumor cell damage leading to tumor cell apoptosis, as well as radiation and treatment parameters that are relevant for an ophthalmic oncologist. We will also discuss the concept of tissue tolerance which is of critical importance when prescribing radiation treatment as well as introduce the principles of three-dimensional conformal radiotherapy and intensity modulated radiotherapy.