The isocentric fast neutron therapy facility at Edinburgh

A second fast neutron beam for radiotherapy has been brought into operation at the Western General Hospital, Edinburgh. This beam is isocentrically mounted and can be rotated through +/- 120 deg from the vertical. Neutrons are produced by bombarding a thick beryllium target with 15 MeV deuterons. The provision of an isocentric facility enables some of the problems associated with poor beam penetration to be alleviated. The physical features of the isocentric facility are described with particular reference to the shielding and the methods employed to overcome problems of neutron activation. Both the prompt radiation leakage and the induced activity have been measured. It has been found that for the first eight months of operation the whole body dose-equivalent to radiographers was approximately 6 microSv (0.6 mrem) per patient treated. Dosimetry associated with the facility is discussed and an example of a seven field treatment plan for a bladder is presented.