Mei, Z.Y. Fan, K. Hu, S. Li, L.X.F. Zeng, Z.J. Zhang, L.G. JACoW Geneva, Switzerland 978-3-95450-182-3 10.18429/JACoW-IPAC2017-THPVA111 English 4716-4718 THPVA111 Contribution to a conference proceedings 2017 2017-05 http://dx.doi.org/10.18429/JACoW-IPAC2017-THPVA111 http://jacow.org/ipac2017/papers/thpva111.pdf A 250 MeV isochronous superconducting cyclotron was adopted in the HUST proton therapy facility. Since the proton beam quality is often limited by the parameters of the central region, special care is given to the design and optimization of the central region to obtain a qualified proton beam using for treatment. An internal proton PIG source with constant arc current is adopted to meet the stability requirements of the beam. Furthermore, a puller followed by an adjustable slit and a fixed vertical collimator are installed to maintain a good centering and vertical focusing beam with maximum intensity. In order to meet the requirement of the intensity modulated proton therapy (IMPT), a vertical kicker is used just followed the puller. The central region structure is optimized iteratively with the simulation results of the OPERA3D and the CYCLONE code. An optimum central region structure has been obtained with RF phase acceptance is around 24°. This paper presents the design parameters of the central region and the results of the proton beam simulation.