Tomotherapy

Tomotherapy is a type of radiation therapy treatment machine. In tomotherapy a thin radiation beam is modulated as it rotates around the patient, while they are moved through the bore of the machine. The name comes from the use of a strip-shaped beam, so that only one "slice" (Greek prefix "tomo-") of the target is exposed at any one time by the radiation. The external appearance of the system and movement of the radiation source and patient can be considered analogous to a CT scanner (computed tomography), which uses lower doses of radiation for imaging. Like a conventional machine used for X-ray external beam radiotherapy (often referred to as a linear accelerator or linac, their main component), it [the tomotherapy machine] generates the radiation beam, but the external appearance of the machine, patient positioning, and treatment delivery differ. Conventional linacs do not work on a slice-by-slice basis but typically have a large area beam which can also be resized and modulated.

==General principles==