Isah: A versatile treatment positioner for external radiation therapy

Mechanical features, control philosophy, and operational characteristics are described for the computer-controlled patient positioner, „ISAH'' (Irradiation Stereotaxic Apparatus for Humans). The positioner is currently being used with the 910-MeV helium-ion beam from the 184”︁ Cyclotron at the Lawrence Berkeley Laboratory. It is capable of positioning a patient to 0.1-mm accuracy in three dimensions. It can simultaneously or selectively translate the patient in three orthogonal axes and rotate him about two perpendicular axes. ISAH is used to deliver a therapeutic dose of radiation to an arbitrarily determined volume within the patient's body during irradiation, so as to minimize exposure to surrounding tissues. The motions are under online control by a PDP-8/1 computer which directs the necessary motions and verifies the positioning. The computer also controls the intensity and the depth of penetration of the heavy-ion beam.