Proton Spot Scanning System Measurement And Analysis

This paper mainly focuses on the commissioning of the treatment heads of key components in domestic proton therapy equipment.The domestic proton therapy device irradiation system adopts a pencil beam scanning method.It requires a high precision for the irradiation position,so it is necessary to accurately measure the position of beam spot.The followings are the mainly works of this article :1.The Lynx-2D commercial fluorescent target product was adopted as a beam spot position measurement tool.With reference to the method of laser spot location,gray center of gravity method and Gaussian distribution method were applied to locate the beam spot image obtained by Lynx-2D.Both are simulated and tested with gaussian noise.On this basis,a mobile test platform was established at the isocenter of the treatment head,and the beam spot position was measured with these positioning algorithms to verify the accuracy.In the actual beam spot position measurement,the stability and accuracy of the gray center of gravity method is superior to the Gaussian distribution method.Therefore,the beam spot is mainly measured by the gray center of gravity method,and the method was developed into a visual analysis software for domestic proton treatment device in the spot position measurement.2.In the spot scanning system,the proton beam is deflected by the scanning magnets to the target region.In the initial stage of the treatment head calibration,it is necessary to know the correspondence between the magnetic field intensity and the deflection position of the beam.By changing the magnetic field strength,the Lynx-2D and the developed software tools were used to measure and analyze the beam spot deflection position.Finally,the calibration relationship of the two variation was established,which provided guarantee for the acceptance and clinical experiment of the next treatment head.3.Through the measurement and modeling analysis of the relationship of the magnetic field and beam position,which ensures the magnet can accurately control the beam,establish three schemes of equal distance lattice,uniform square radiation field,and pattern scanning to test the scanning system performance.In the 16-pitch array,the average position deviation of the individual beam spots in the X direction is within 0.4 mm,and Y direction is within 0.2 mm.The profile flatness of the uniform square radiation field in the X direction is 5.14%,while Y direction is 2.09%.The pattern scanned on the Lynx-2D clearly reflects the characteristic of original image.The test results showed that the accurate beam spot location method and the reliable corresponding relationship between the magnetic field intensity and beam spot deflection position were established in the early stage,and provided the technical basis for the subsequent irradiation treatment plan.The above work lays the foundation for the calibration of the treatment in the next time and helps the device to enter the clinical experiment as soon as possible.