A Versatile Patient Positioner for Radiation Therapy

Mechanical features, control philosophy, and operational characteristics are described for the automatic, computer-controlled patient positioner "ISAH." This device is presently in operation at LBL's 184-Inch Cyclotron. It is capable of positioning a patient or experimental animal to 0.1 mm accuracies in three dimensions. It can simultaneously or selectively translate the patient in three orthogonal axes and rotate him about two perpendicular axes. Translational motions are 61, 40 and 23 cm respectively while rotations are 400 deg. It is used to deliver a therapeutic dose of radiation from the cyclotron (910 MeV Helium ions) to an arbitrarily defined volume within the patient's body and to manipulate the patient during irradiation so as to minimize radiation exposure of the intervening tissue. The patient motions are under on-line control of a PDP-8/I computer which directs the necessary motions and verifies their performance. The computer may also control a variable thickness water column used to vary the depth of the Bragg peak within the patient.