Design Of The Gantry Beamline For A Proton Therapy Facility

Cancer is the second leading cause of death in worldwide.Nowadays,proton therapy is one of the most advanced non-invasive precision therapy methods for cancer,which utilizes the unique Bragg peak characteristics of protons.By adjusting its peak depth precisely,the dose of tumor cells will be maximum and normal organs around the tumor are furthest protected owing to the dose optimization of multi-radiation field which achieves the best therapeutic effect.Compared with other cancer treatment methods,proton therapy has the advantages of higher efficiency,lower side effects,and wide indications.However,proton therapy facility has a high technical threshold and the construction cost is very high.The related technologies are almost monopolized by foreign countries and have strong commercial confidentiality.The research materils are quite limited,and the development of domestic proton therapy technology is just beginning.Therefore,the realization of domestic proton therapy facility development will break the monopoly of foreign technology and reduce the cost of treatment.This is of great significance for relieving the common people's medical problems in the country.In a proton therapy facility,the gantry beamline is one of the key component of the beam transport system,including magnets,vacuum,beam diagnostics,mechanical support and other subsystems or components.The weight of whole gantry is about 200 tons,of which the beamline weighs about 40 tons.However,it requires the beam accuracy at the iso-center shall be better than 1 mm.Thus,the design,construction and commissioning of the gantry beamline is also one of the major technical difficulties of the beam transport system.Based on this project,this thesis completes the comprehensive theoretical research and related engineering design of the gantry beamline:The physical design of the gantry beamline is the core and foundation of this paper,and mainly includes the beam optics design and the dynamic scanning magnets design.Both of these two parts determine the layout of the gantry beamline,and effect the gantry structure,radius and cost.In the physical design,the downstream scanning scheme of the gantry beamline is firstly compared and determined,and on this basis the image beam optics design and match are introduced.Then the need of magnet design specifications are proposed;for the design of the scanning magnets,the clinical and physical requirements of the scanning system and the engineering index of the magnets are proposed.Then the design of the magnets and the eddy current effect analysis are completed.The eddy currents can be effectively reduced by adding slits at the end of magnet,and different magnet coil shapes,slits directions,distribution and width are compared to obtain the optimal configuration.Finally,the maximum temperature of optimized magnet is lower than 70 C,meeting the design requirements.In the magnet error analysis,the source,classification and influence of magnet errors are introduced firstly.The error of each type of magnet is analyzed and calculated in detail,and the transmission matrix containing the error term is obtained at the same time.The principle of the beam alignment technology,the solution and acquisition method of the response matrix are introduced.This technology is applied to the HUST-PTF facility,optimizing the layout of correctors in detail and completing the beam correction calculation.The results show that the accuracy of center beam trajectory is better than 0.5 mm,meeting physical and clinical requirements.In the design of auxiliary systems,we complete the design of vacuum system,beam diagnostics system and magnet mechanical support system.For the vacuum system,the vacuum film material and size are compared and selected with regards to the perspective of deformation and beam penetrability.The size of the vacuum pipe is determined and select the appropriate vacuum components to constitute the vacuum system.Combined with the beam based alignment calculation and the beam measurement requirements,the measurement elements are chosen and distributed.The principle and structure of the plate ionization chamber used in the gantry beamline are analyzed theoretically in detail.With electronics and control devices,an ionization chamber measurement system is set up.For the magnet mechanical support system,we complete the design of magnet support structure.When the gantry rotation angle is 0-degree,90-degree and 180-degree,the maximum deformation and stress meet the design requirements.