1.1 - Movements Of The Linac

Modern linear accelerators typically have three movements:

Gantry Movements

  • The gantry rotates around a central point (the isocentre), which is always the same distance from the treatment head. The gantry can typically rotate just over 180o in each direction from the neutral position.

Collimator Movements

  • The collimator or treatment head can rotate around the axis which passes from the isocentre to the target. This rotation is usually about 180o in each direction as well
    • For linear accelerators with dynamic wedges, the jaws which create the wedge are usually limited to a single pair; therefore wedging may only be performed along one axis. To wedge in the other axis, the collimator must be rotated.

Couch Movements

  • The treatment couch in most linear accelerators can move in six directions - up, down, left, right, forwards and backwards.
  • The treatment couch in modern linear accelerators is also capable of rotating 90o in each direction from the neutral position.
    • These movements are important when junctioning of fields is required.