The TomoTherapy treatment system delivers radiation therapy with a spiral delivery pattern (TomoHelical™) or discrete-angle approach (TomoDirect™). Photon radiation is produced by a linear accelerator (or linac for short), which travels around the patient and moves in unison with a device called a multi-leaf collimator, or MLC, that shapes the beam. Meanwhile, the couch is also moving—guiding the patient slowly through the center of the ring.