Development Of A High Sensitivity Beam Spot Detector For The HUST Proton Therapy Facility

Cancer is currently the biggest threat to human health.China has 4.3 million new cancer patients and 2.8 million deaths each year.The diagnosis and treatment of cancer is a major issue concerning the national economy and people’s livelihood.Among the many cancer treatments,proton radiotherapy is considered to be one of the most accurate non-invasive treatments due to the unique Bragg Peak of the proton beam,which minimizes damage to normal tissues.Huazhong University of Science and Technology and China Institute of Atomic Energy hosted the National Thirteen-Five Key R&D Program “Proton Therapy Faculty based on Superconducting Cyclotrons”(HUST-PTF).HUST-PTF consists of 250 MeV Superconducting Cyclotrons,beam transfer line,the treatment room and the corresponding control system.Based on this project,this paper focuses on the system design and research of the beam spot detector,which is the most popular on the beam transport line.The beam position and profile measured are so important on the beam transfer line that they are basis of orbit correction,energy,divergence and emittance measurement.The beam spot detector is the first choice for the advantage of stable and economical measurement.The beam energy is 250 MeV after extracted from cyclotron.After the energy selection system,the energy will vary between 70 and 240 MeV,and the beam intensity ranges from 0.4 nA to 10 nA,which brings new challenges to the design of the beam spot detector..In order to meet the requirements of HUST-PTF beam diagnosis,the beam spot detector was designed in detail.Firstly,analyze the illuminance and linear dynamic range of different materials,and select the thickness of 1mm,the diameter of 68 mm Al2O3:Cr ceramic material as the target screen according to the parameters of the beam;secondly,compare the inclination angles of different illuminating screens,the observation angle of the camera,combined with the limited spatial range of the transport line,and make a conclusion that the camera tilt 90° along the beam direction in the optical structure and the illuminating screen tilt 45° to the beam direction,which enables the system to obtain higher resolution;Thirdly,the radiation effect of the beam bombardment illuminating screen is analyzed by Geant4 and FLUKA under the premise of determining the beam parameters.And the radiation condition of the CCD chip at the camera,judging that the period of replacing the CCD is one quarter,to further reduce the radiation effect,the working distance can be increased to 230 mm or the lead glass shielding material is used;finally,based on the beam spot illumination captured by the CCD camera,LABVIEW software are used to process image with image correction,contrast stretching,filtering,etc.Off-line calibration results in the resolution 0.13mm/pixel,which verifies the reasonable authentication scheme.At the same time,based on the beam spot detector method,the key parameters on the transport line are measured and analyzed.