ABSTRACT
The treatment of human cancer by ionizing radiation has developed over the past century into one of today’s most effective modalities for managing this disease. Along with surgery and chemotherapy, this type of treatment comprises the major clinical tools for treating the cancers that will be detected this year and well into the future. Currently, radiation treatment alone or combined with other modalities is the preferred therapy for over 50% of all cancer pathologies. The protocols for radiation treatments in current use for various cancers were established mainly by empirical clinical experience over several decades. These have attempted to achieve a high level of killing of clonogenic tumor cells within planned treatment volumes (PTVs) while producing minimal or acceptable damage to the normal tissues that will inevitably be exposed to some dose of radiation during the treatment. The efficiency of tumor response (cell kill) relative to normal tissue complications is called the “therapeutic ratio” (TR), although TR is usually not defined quantitatively.
