4D radiotherapy refers to any of the techniques when the movement of the tumour is taken into account, not only during treatment but also during planning. This means that when the CAT scan system is scanning the patient, it not only acquires images at a particular moment, but also a series of images with the treatment area in the different positions it can adopt. The planning system then uses these images to reproduce the real movement of the patient.
This technique is mainly used for lesions of the lungs which have continuous movement and whenever the patient's condition so permits.
In the IMOR Institute it is used for 'gating', which consists of irradiating the tumour only when it is in a certain position to prevent against irradiating healthy tissues