Analysis And Measurement Of Out-of-field Radiation Field Of 6 MV Linear Accelerator

Cancer has plagued mankind since the dawn of time.In order to treat cancer more effectively,cancer treatment methods have evolved from the traditional three treatment methods to the five treatment methods available today.They are surgical resection treatment,chemotherapy and radiation therapy among the traditional treatment methods and immunotherapy and palliative treatment among the new treatment methods.Among these methods,radiation therapy is one of the effective solutions to the cancer problem,with more than half of the cancer patients requiring this method during their treatment.Radiation therapy methods are also evolving in practice,with a variety of new radiation therapy methods emerging on the basis of the conventional radiation therapy.However,while these methods have improved the cure and survival rates of patients,they still have the problem of radiation therapy causing secondary cancers out of field.This problem is mainly due to the fact that when radiation therapy is administered,the out-of-field tissues or organs can absorb radiation doses that exceed safety standards,increasing the risk of cancer in the out-of-field tissues or organs.Therefore,when using radiation therapy to treat cancer,it is important to ensure not only that the target cells are exposed to sufficient radiation,but also that the tissues or organs outside the treatment area are exposed to radiation within the safety standards.The out-of-field radiation field of the 6 MV linear accelerator,which is commonly used in radiotherapy,have therefore been analyzed and measured.The photon distribution and electron distribution of the out-of-field radiation field in radiation therapy was first investigated.Two models of medical linear accelerator treatment heads with and without flattening filter were constructed according to the instructions provided by the manufacturer of the Varian Unique medical linear accelerator,and the validation of the reasonableness of the treatment head model was achieved by comparing the results of two characteristic curves obtained from simulations and ionization chamber dosimeter measurements,i.e.the percent depth dose curve and the off-axis ratio curve.The curves of photon flux and electron flux as a function of water depth were measured for different fields and off-axis distances in order to investigate the distribution of out-of-field photons and electrons.Since the number of electrons in the radiation field is small,the out-of-field photon distribution at different energies,i.e.the photon energy spectrum,have been investigated.Finally,the scattered dose radiation of the out-of-field radiation field in radiation therapy was investigated.Simulations were carried out to measure the total scattered radiation and the dose distribution of the different components of the scattered radiation in the radiation field.The distribution of the out-of-field radiation field of the 6 MV medical linear accelerator was measured under realistic radiotherapy conditions using a film dosimeter.The analysis and measurement of the out-of-field radiation field of the 6 MV linear accelerator was achieved after the investigation of the particle distribution and the scattered radiation dose in the out-of-field radiation field of the radiotherapy treatment was completed.