On Achieving a Clinically Useful D-T Neutron Isocentric Therapy System

The escalation of minimum acceptable design goals for a "clinically useful" sealed D-T neutron generator tube appears to be leveling off after the requested tube lifetime output has been increased 4000 fold. Perhaps for the first time in the 15-year developmental evolution, we are now delivering a hospital system definable as "clinically useful" without being leapfrogged by another new set of yet higher requirements. The Cyclotron Corporation\´s Model 4100 Neutron Cancer Therapy System with its output of 8 × 1012 (14 MeV) neutron/sec designed for 500 hours is made up of: a factory recyclable miniature 200 kV sealed tube which radially accelerates up to 450 mA of deuterium and tritium ions from four duoplasmatron-type ion sources onto a central target; hand changeable radiation collimators; boronated hydrogenous shielding; isocentric gantry mounting; clinical diagnostics; and controls. The self-contained gas handling system which provides the needed differential gas pressure also stores, pumps, cleans, and recycles the D-T inventory. It is composed of a reversible getter high vacuum pump, a selective noble gas sputterion pump, and a specialized uranium trap which, by controlled thermal decomposition of uranium hydride, regulates the ion source pressure. A D-T gas inventory of 3.7 k curies provides beam-on time of about three hours, while the gas recycle requires one to two hours. The four-sided target is made up from an array of heat transfer-optimized small copper tubes and their metal surface cladding which results in relatively high neutron output and long target life.