Monte Carlo Simulations On The Ion Beam Therapeutic Performances Under Different Scenarios

Heavy ion beam is considered as the most potential therapeutic ray because of its unique Bragg peak and high relative biological effects.In the research field of heavy ion therapy,various peripheral auxiliary technologies and heavy ion irradiation methods have been expanded and made great progress at the same time.For example,the positioning verification technology developed from X-ray imaging technology,combined with the optimization of heavy ion radiotherapy process,forms a positioning automatic image-guided heavy ion radiotherapy technology.The biological effect evaluation technology of heavy ion radiotherapy based on nanodosimetry has made heavy ion radiotherapy move towards the step of biological conformal intensitymodulated precision irradiation technology.At present,in the field of image-guided heavy ion radiotherapy,the role and importance of magnetic resonance image-guided heavy ion therapy in radiation oncology are increasing rapidly with the development of magnetic resonance imaging（MRI）technology.Heavy ions have their own charge,which makes them subject to the Lorentz force that photons do not have in the magnetic field,and then the beam deflects as a whole,resulting in changes in the beam and dose distribution.At the same time,the basic parameters of the evaluation technology of heavy ion radiobiological effects-the dose average LET and the nanodosimetric quantities-will also change accordingly.Only by exploring the relationship between the change and the magnetic field,in order to make the magnetic resonance image-guided technology better combined with heavy ion radiotherapy.In the heavy ion irradiation method,in order to reduce the treatment uncertainty related to heavy ion therapy and maintain the potential to enhance tumor control,the optimization strategy of single ion and multiple ion combination is proposed.In the multi-ion radiotherapy method,by combining two or more types of ion irradiation,we can achieve constant relative biological effectiveness（RBE）in a single field,achieve uniform physical dose and RBE in the target volume at the same time,and provide more robust distribution in physics and biology.In contrast,in conventional particle therapy,a constant RBE can be achieved only by providing a multi field setting（e.g.for the penetrating field）.Clarifying the variation law of dose average LET and nanodosimetric quantities in the case of multi-ion radiotherapy will be conducive to the rapid deployment and implementation of multi-ion radiotherapy.In this paper,the Monte Carlo simulation platform GATE with GEANT4 as the core is used to simulate the dose average LET and nanodosimetric quantities of carbon ion beam under magnetic field and the changes of dose average LET and nanodosimetric quantities of various ion beams in the model.Firstly,the distribution of dose average LET of carbon ion beam in vertical and parallel magnetic field environment is simulated.The results show that the change of dose average LET of carbon ion beam in parallel magnetic field environment is within1%,while the dose average LET of carbon ion beam in vertical magnetic field will produce obvious lateral deflection.Secondly,nanodosimetric quantities is a theory that describes the ion micro track structure at the nano scale.The expression of ion micro track structure at the nano level can reveal more information related to biological effects than the macro dose average LET and micro dosimetry.In this paper,the distribution of nanodosimetric quantities of carbon ion beam with different energy in different magnetic field environment is explored through Monte Carlo simulation.According to the analysis of simulation results,in the environment of parallel magnetic field,the change of carbon ion beam nanodosimetric quantities is not significant,and the influence of vertical magnetic field on nanodosimetric quantities is more significant.This is mainly due to the deflection of carbon ion beam by vertical magnetic field,which leads to the change of dose average LET at the same penetration depth,and the corresponding change of carbon ion beam nanodosimetric quantities.Finally,aiming at the situation of multi-ion radiotherapy therapy,this paper simulates the distribution of dose and dose average LET of different ions in the phantom,and then compares the differences of nanodosimetric quantities of different ions combined with the algorithm of nano dosimetry.In the specific method,different ion beams with different energies are simulated,the relationship curve between range and energy is fitted,and the research is carried out when the range is 15cm.The differences of dose and dose average LET distribution of different ions with the same proton number were compared.Further compare the distribution of differention nanodosimetry.The research in this paper shows that the distribution of dose average LET and nanodosimetric quantities of carbon ion beam changes significantly in the environment of vertical magnetic field.It provides reference data for the changes of various physical quantities of carbon ion beam in magnetic field environment during magnetic resonance guided radiotherapy.At the same time,the dosimetry of different ions was compared,which provided a basis for the development of multi-ion radiotherapy therapy.