The design of an adjustable half block for nonasymmetric linear accelerators

Half-block techniques in radiotherapy may be used to junction two abutting radiation fields. Removable half blocks for linear accelerators not equipped with asymmetrical jaws can accomplish this technique providing the block edge is properly secured with respect to the beam central axis to achieve a smooth beam junction. Successive block edge cuts with a milling machine are, however, required to achieve an acceptable junction of the fields. The design of a half-block device that allows secure adjustment of the block edge on the linac thus alleviating the need for successive milling procedures is presented.