Isocentric technique

An isocentric technique is one where all beams used in a radiation treatment have a common focus point, a.k.a the isocentre.

The movements of the linac are three fold:

1. the gantry rotates (like a big crane arm)
2. the collimator twists (the head of the gantry)
3. the bed swings around

File:Linac Collimatortwist.png

All of these movements in the modern linac occur around an axis that runs through the isocentre. In this way, if the centre of the target area in the patient's body is moved to coincide with the isocentre, then all motions of the machine will remain centred on the target.