Study Of The Scanning Algorithm For The Spot Scanning Beam Delivery System

The main functions of the proton beam delivery system is to convert the proton beam extracted from the accelerator to treatment beam,and deliver the treatment beam to the target tissue.The key point of the beam delivery system is the precise control of the proton beam position at the ISO center.Beam delivery system can be divided into passive and active beam delivery system.Passive beam delivery system use scattering method to reduce the proton energy and broaden the beam so as to achieve an adequate dose distribution at the treatment volume.Active beam delivery system directly delivery the beam to the target by using scanning magnets to broaden the beam and by adjusting the beam energy.The main components of the active beam delivery system are scanning magnets and ion chamber.The structure of the active beam delivery system is much simpler than that of the passive beam delivery system.Moreover,it has the advantage of high beam utilization rate and smaller penumbral width and distal dose falloff(DDF).The active beam delivery system can be divided into spot scanning and raster scanning.During the spot scanning,beam is turned off when moving from one spot to another,while beam is not turned off for the raster scanning.Shanghai Advanced Proton Therapy Facility(APTRON)adopts spot scanning beam delivery system.The target of the beam position control system design is to precisely delivery the proton beam to the lateral position prescribed by the treatment planning system.Its main functions are controlling scanning magnets,eliminating the magnetic hysteresis effect,removing the scanning magnetic field error,beam position error and various alignment error by using feedback controlling system so as to achieve a precise beam position.In this thesis,we calculated the design specification of the spot scanning beam position control system by Monte Carlo simulation according to the design specification of the beam delivery system.We have designed the control system architecture and the controlling algorithm according to the existing hardware.We have verified our beam position controlling system by using real proton beam.The thesis is helpful for understanding the design of spot scanning beam position control system.