Abstract: There is herein provided a method of identifying an isocentre of a radiotherapy apparatus. The method includes capturing illumination of respective dummy point images at rotational positions of a component of the radiotherapy apparatus at an image capture device mounted on the radio-therapy apparatus and deriving the isocentre from the captured dummy point images.

Abstract: Disclosed herein is a radiation head for a radiotherapy device. The radiation head comprises a source of radiation configured to emit a beam of radiation; and beam shaping device for collimating the beam of radiation. The beam shaping device comprises a multi-leaf collimator; and a diaphragm positioned between the source and the multi-leaf collimator. The diaphragm comprises a diaphragm block movable along a curved path, the diaphragm block having a flat face focused on a focus point which is offset from the source of radiation.