Isocentric technique
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An isocentric technique is where all beams used in a radiation treatment have a common focus point, a.k.a. the isocenter. Isocentric techniques require less patient repositioning as multiple field arrangements can be delivered with gantry and collimator movements, reducing treatment times.[1]
The idealized intersection point of the gantry axis of rotation with that of the collimator and treatment table is known as the mechanical isocenter[2]
In practice, due to the heavy weight and mechanical imperfections of the system, the isocenter is not a single point and its location changes with the rotation of the gantry, collimator or couch. This causes small uncertainties in the determination of isocenter position, typically less than 2 millimetres[3]
