Dose Verification Of Radiotherapy For IMRT And Dosimetric Characteristics Of Flattening Filter Free Beam

Radiation therapy plays an important role in the cancer treatment, which aims atmore precise beam control with, better efficacy and less damage. Intensity modulatedradiation therapy (IMRT) is dominate technology in current precise radiation therapy,since multi-leaf collimator (MLC) and the large gradient change in IMRT can lead tolarge bias in conventional dose calculation. In order to ensure the quality of radiationtherapy and better calculation of dose distribution in IMRT, this work considers factorsthat affect dose distribution and corresponding function, and establish linear acceleratortreatment head model, the radiation environment model and the real patient CT imagevoxel model. By using the Monte Carlo program BEAMnrc and DOSXYZnrc we obtainmodular and combination calculation in those models, and develop a direct dosecalculation method and simulate the multiply fields exposure in IMRT to calculate dosedistribution of human body. In addition, we calculated dose distribution in simulationwithout flattening filter in linear accelerator. The dosimetric properties of flatteningfilter free photon beams were evaluated compared to conventional flattened beam,which indicate the advantage of unflattened beams in clinical radiation therapyapplication. The results of this study provided the basis of theoretical calculations forIMRT technology and development of new radiotherapy technique. Also, it provided areference basis for radiotherapy clinical application, quality assurance and qualitycontrol. This paper is organized as follows:1. A Monte Carlo program was used to modular establish linear acceleratortreatment head model, the radiation environment model, water phantom model and thereal patient voxel model based on manufacturer and hospital-provided information. Thedose distribution in water phantom was calculated and compared with measurements tovalidate our MC model.2. The dose distribution of flattening filter free photon beam was calculated and thedosimetric characteristics were estimated. Several dosimetric characteristics were compared with flattening filter photon beam, proposing the advantage and prospects ofits application in radiotherapy.3. A conversion method of CT image to MC Voxel model was described, by usingCT image to establish real patient model and simulate IMRT treatment process tocalculate the dose distribution of tumor target. The isodose curves in the plane ofisocenter were calculated to explain the dose distribution in real patient. Additionally,this paper calculated the dose distribution of photon beams with and without flatteningfilter in patients.