Rotational/helical/arc intensity-modulated radiation therapy

Radiopaedia • CC-by-nc-sa 3.0 • de

Rotational/helical/arc intensity-modulated radiation therapy (IMRT) is the most advanced form of IMRT is conceptually similar to helical or cone-beam CT . The radiation beam remains turned on throughout the treatment while the gantry is moved around the patient at variable speed and the multi-leaf collimator (MLC) simultaneously varies the shape of the beam.

Several competing implementations are available:

  • tomotherapy (i.e. 'slice' therapy)
    • modulated fan beam delivers radiation in a helical pattern
    • several rotations of the beam are delivered while the patient moves through the machine
  • volumetric arc therapy (VMAT)
    • broad beam is shaped by an MLC as it goes around the patient in an 'arc'
    • typically only a single arc is used, more complex treatments may use 2-3 arcs
    • patient does not move during each arc but may be re-positioned between arcs