Beam monitor system for high-energy beam transportation at HIMAC

Heavy-Ion Medical Accelerator in Chiba (HIMAC) provides ion beams for radio therapy of cancers and for other basic researches. High-energy beam transpo rt lines deliver the beams to three treatment rooms and two experiment room s with. the aid of 41 beam monitor units. Each monitor unit consists of a w ire grid as a profile monitor, or a combined unit in which the wire grid an d a parallel plate ionization chamber are united for an additional measurem ent of a beam intensity. They are operated in a mixed gas of 80% Ar and 20% CO2. The gas gain of the wire grid achieves about 8000 at an applied volta ge of - 2700 V. Dynamic ranges of the wire gird and the parallel plate ioni zation chamber were measured to be 8 x 10(5) and 1 x 10(6) in test using io n beams, respectively. A control system of these monitor units offers easy operation, so that operators are almost free from miss-operations. The moni tor units are interlocked with a system which protects patients from the un desired irradiation. Five wire grids are used for continuously monitoring t he beam during treatments, which play a role in keeping qualities of the tr eatments. The monitor system has been designed to meet requirements for med ical uses, and works in a stable and reliable manner and satisfies the requ irements. (C) 1999 Elsevier Science B.V. All rights reserved.