| Proton and heavy ion therapy technology is internationally recognized as the most advanced radiation therapy technology.Compared with traditional radiotherapy(including X-rays,photons,electrons,etc.),proton and heavy ion beams generate a Bragg peak distribution with high linear energy transmission(LET)at the end of the range of human tissue,which lays the physical advantages of protons and heavy ions in tumor precision therapy.During the treatment,the beam delivery system precisely delivers the main dose of the beam to the tumor target,achieving the maximum irradiation dose to kill tumor tissue while minimizing damage to surrounding normal organs and tissues.However,to make full use of the physical advantage of the Bragg peak in proton and heavy ion precision therapy,it requires not only accurately locate the tumor location,but also accurately evaluate the radiation dose required for the tumor site during the treatment process.Currently,tumor radiation dose is evaluated by making a treatment plan first and then verifying it.However,during the treatment process,the distribution of radiation dose may be different from the dose distribution of the treatment plan,resulting from individual differences,respiration,organ movement,and other factors.This may be cause tumor recurrence or influence to normal organ tissues.The existing treatment systems measure the beam position and dose before injected into human tissues through terminal dose and position monitoring systems.But with this method the accuracy of beam dose distribution in real time during the actual irradiation process cannot be evaluated.Therefore,for the treatment of radioactive tumors,the real-time dose distribution accuracy assessment during the treatment is a very challenging problem.In order to solve the problem,it is urgently needed not only to improve the performance of the terminal detector in terms of measuring energy range,measurement accuracy,response time and beam energy loss,but also to establish a realtime monitoring and measurement system for three-dimensional(3D)dose in vivo with short measurement time and high accuracy.Based on the above problem,this thesis mainly focuses on the development of terminal detectors and the research of 3D dose reconstruction technology.The specific contents are as follows:·A strip electrode profile detector for the radioactive beam line HFRS of the High Intensity Heavy-ion Accelerator Facility(HIAF)has been developed.It can operate in secondary electron mode,ionization mode and proportional mode.It can meet the needs of long-term work in high radiation environment.The measurement range of the detector can be adjusted by changing the internal pressure,working voltage,and integration time of the electronic system of the detector.It can monitor the fast and slow extraction beam with an intensity range of more than 6 orders of magnitude,and with the position resolution of ≤0.1 mm.·A uniformity monitoring detector for the terminal of the Space Environment Simulation and Research Infrastructure(SESRI)has been developed.The detector can monitor the uniformity of low energy He beam～Bi beam,and U beam under low vacuum condition(<100 mbar).It can also monitor the uniformity of proton beam under an atmospheric pressure environment.Both the detector and the strip electrode profile detector can monitor almost all types of particle beams on the particle accelerator.·Based on the strip electrode profile detector and the terminal uniformity monitoring detector,the terminal detector of FLASH radiotherapy(FLASH)has been pre-developed.The detector scheme design has been completed,providing a design reference for the subsequent FLASH radiotherapy real time monitoring system.·A new generation of integrated Bragg peak detector has been developed for Quality Assurance(QA)monitoring of Heavy Ion Medical Machine(HIMM)and proton ion therapy devices.The detector has no dead time,and the minimum integration time is 44.2 μs.The detector can measure therapeutic energy of all protons and carbon ions,with an energy range accuracy better than 0.2 mm.The test results show that the range deviation is less than 1 mm after the calibration of the water tank.The energy range accuracy of several single energy proton beams and carbon ion beams has been tested using the detector.·An integrated dose position monitoring ionization chamber has been developed for monitoring the beam at the gantry of HIMM and proton ion therapy devices.The ionization chamber has 256 channels in X and Y directions and no dead time,with integration time ranging from 44.2 μs to 2.584 ms,position resolution less than 0.1 mm,noise level better than 0.2 nA,and water equivalent thickness less than 0.8 mm.The dose monitoring part of the ionization chamber has been tested for dose counting,counting calibration,off axis response,and dose response time.The ionization chamber has measured online beam profile,beam spot position deviation,beam spot size deviation,beam field symmetry,and uniformity on HIMM and proton ion therapy device.·A 3D dose reconstruction method based on database calculation was proposed for the first time,and a 3D dose distribution experimental measurement system was designed and experimentally validated.The experimental measurement system is composed of the striped ionization chambers,a respiratory motion simulation device,and a polymethyl methacrylate(PMMA)phantom.It can achieve synchronous collection of data such as beam position distribution,dose intensity and angle of the beam,and 3D dose distribution in the phantom.The dose distribution data of six therapeutic energies between 160.86 MeV/u and 211.44 MeV/u under single point,four points,static and moving wedge models has been measured.The dose distribution data of the single point,four points,and stationary wedge phantom has been used as the basic data for the 3D dose reconstruction algorithm,and the multi-point dose distribution data under the moving wedge model is used as the validation data for the reconstruction algorithm.By comparing the reconstruction results with the measured results,it can be concluded that when the voxel was 2 mm,the maximum position deviation was 2.56 mm,the average position deviation was 0.86 mm,the maximum dose deviation was 23.3%,and the average dose deviation was 10.39%.The offline reconstruction time was approximately 56 ms which was close to the expected results.The results of this experiment verify the feasibility of 3D dose reconstruction in the uniform phantom.By simulating the organ displacement of human respiratory movement through a moving wedge phantom,3D dose reconstruction and respiratory correction in the phantom can be realized. |
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