An adjustable cradle assembly (100, 100', 100") for adjusting a head fixation apparatus relative to a patient platform, the adjustable cradle assembly comprising: a base (110, 110', 110") comprising a locking or securing mechanism for releasably locking the base to the patient platform, and a pair of vertical support members or tabs, each vertical support member or tab having at least one position aperture or slot (222, 224) for setting a vertical height relative to the platform; characterised in that it further comprises a cradle comprising a curved channel configured to releasably receive a head fixation ring, wherein the cradle is configured to span between the vertical support members or tabs of the base such that the channel aligns between the vertical support members or tabs, and at least one adjustment connection point, wherein each adjustment connection point of the at least one adjustment connection point is configured for alignment with the at least one position aperture or slot of a corresponding vertical support member or tab of the pair of vertical support members or tabs; and at least one adjustment mechanism, wherein each adjustment mechanism of the at least one adjustment mechanism is configured to releasably connect to a respective adjustment connection point of the at least one adjustment connection point of the cradle through a selected position aperture or slot of the at least one position aperture or slot of the respective vertical support member or tab of the pair of vertical support members or tabs to lock the cradle to the base at a selected lock position; wherein, upon locking at the selected lock position, the cradle is aligned at a selected vertical position above a patient platform and at a selected pitch angle relative to a plane perpendicular to the patient platform. a base (110, 110', 110") comprising a locking or securing mechanism for releasably locking the base to the patient platform, and a pair of vertical support members or tabs, each vertical support member or tab having at least one position aperture or slot (222, 224) for setting a vertical height relative to the platform; characterised in that it further comprises a cradle comprising a curved channel configured to releasably receive a head fixation ring, wherein the cradle is configured to span between the vertical support members or tabs of the base such that the channel aligns between the vertical support members or tabs, and at least one adjustment connection point, wherein each adjustment connection point of the at least one adjustment connection point is configured for alignment with the at least one position aperture or slot of a corresponding vertical support member or tab of the pair of vertical support members or tabs; and at least one adjustment mechanism, wherein each adjustment mechanism of the at least one adjustment mechanism is configured to releasably connect to a respective adjustment connection point of the at least one adjustment connection point of the cradle through a selected position aperture or slot of the at least one position aperture or slot of the respective vertical support member or tab of the pair of vertical support members or tabs to lock the cradle to the base at a selected lock position; wherein, upon locking at the selected lock position, the cradle is aligned at a selected vertical position above a patient platform and at a selected pitch angle relative to a plane perpendicular to the patient platform.