The Sheffield stereotactic radiosurgery unit: physical characteristics and principles of operation.

A stereotactic radiosurgery unit was commissioned in Weston Park Hospital in the summer of 1985. This paper describes the design, principles of operation and the safety features of the multiple-beam cobalt-60 therapy unit. The measurement of the dose around the extremely sharp focus produced by the 201 beams is discussed and the results compared with computed distributions. The results of the radiation protection survey are presented and the design of the purpose-built treatment suite is discussed. The procedure for treatment of a patient is outlined.