Beam-energy-related operation control for carbon-ion therapy system

We propose a beam operation control method for radiation protection at an ion-beam accelerator facility. In the method we need to set two parameters, i.e. a maximum beam operation energy and a product of a beam intensity, an injection time per week and a square of the beam energy for each beam-loss (radiation source) point. The beam operation control is done so as not to exceed the values. That enables flexible beam operation in terms of beam intensity, time and energy, and prolongation of the beam operation time when the beam energy is lower than the maximum one given as the loss condition. It is explained by the fact that the neutron yield is proportional to the square of the incident beam energy, which is supported by the published experimental data and our simulations in the energy range of treatment operation. (author)