Research On The Relative Biological Effectiveness Of Ion Beams Based On Microdosimetry And Nanodosimetry

Based on the inverted depth dose distribution and the relatively high biological effect near the Bragg peak,ion beam is recognized as the most advanced and promising radiotherapy ray by the international radiotherapy community.Relative biological effectiveness(RBE)is an important parameter in ion-beam therapy.Since the factors affecting ion-beam RBE are very complex,it is necessary to establish the biophysical model to calculate RBE in ion-beam therapy.However,the extant RBE models have many shortcomings,which seriously restrict the further development of ion-beam therapy.Therefore,in this work,investigations focus on the ion-beam RBE are performed.On the one hand,the extant microdosimetric RBE model is improved and expanded.On the other hand,a new RBE model based on nanodosimetry is established.In addition,several clinically relevant RBE problems are investigated.The main content of this dissertation is shown as follows:(1)Based on the theory of microdosimetric kinetic model(MKM),the ideal tissue equivalent proportional counter combined with the Gate Monte Carlo(MC)simulations are introduced to accurately calculate the biological dose of ion beams.This method improves the accuracy and reliability of MKM-based RBE calculations in ion-beam therapy.What’s more this approach can be applied to different ion-beam-treatment centers easily,and provide helpful reference for clinical treatment.(2)The nanodosimetric data set obtained by the track structure MC simulations combined with the condensed history MC simulations is introduced to the calculation of nanodosimetry in ion-beam therapy.A novel RBE model(Logistic nanodosimetry model,LNDM)based on nanodosimetry is then established.What’s more,the accurate calculation method to the clinical RBE is then established.The systematic verifications in this work show that the accuracy of LNDM model is better than all other extant models.The calculation method of ion-beam RBE is extended from microscale to nanoscale.This helps to improve the accuracy and reliability of ion-beam RBE calculations.What’s more,many deficiencies of the extant RBE models are improved.This is helpful for ion beams to play all its potential physical and biological advantages in clinical scenarios.(3)Theoretical study on the magnetic field effect on the microdosimetry of ion beams is performed for the first time.Combining with the conclusions on the magnetic field effect on the nanodosimetry of ion beams,it is concluded that: within the clinical MRI magnetic field strengths,magnetic field has no effect on the microdosimetry and nanodosimetry of ion beams,and it will not affect the RBE of ion beams.The investigation on the dependence of RBE on fractional dose in carbon-ion therapy shows: with the increase of fractional dose of carbon-ion beams,the RBE values of tumor cells were always higher than that of normal tissue cells regardless of their radiation sensitivities.In addition,the abnormal phenomenon of increasing RBE with fractional dose is found.These results are of great significance for the development of MRI guided and hypo-fractionated ion-beam radiotherapy.The research in this dissertation established an accurate and reliable RBE calculation method for ion beams,which improved some shortcomings in the extant RBE calculation methods.What’s more,this dissertation provided a useful reference for the realization of accurate ion-beam therapy.