Monte Carlo Simulation Of Target Location In Proton Therapy

Since the concept of proton therapy has been put forward,proton radiotherapy technology has been widely concerned and rapid development.Precision radiotherapy is the current mainstream direction,in which "precise positioning" is a good start to precision radiotherapy,more concerned by the researchers.At present,on-line monitoring of target location is generally carried out by annihilation gamma-ray imaging.However,this method of positioning bias in the range of a few millimeters or even centimeters,the error is large,so the "precise positioning" put forward higher requirements.In recent years,Monte Carlo method has become one of the most commonly used methods in the design and optimization of medical research.In this paper,we use this method to reconstruct the annihilation photons generated by proton therapy,and propose a new way of positioning,which greatly improves the positioning accuracy.Proton reacts with¹⁶O in the human body to produce positron nuclide13 N,which decays and releases positrons.Positrons and electrons are annihilated to release photons.The target location is performed by tracking the position of the photons and the energy deposition of the protons on the path.In this paper,the MCNPX program was used to simulate the transport of proton beams with energy of 60 Me V-150 Me V in muscle tissue and 90 MeV protons in GTV?tumor target?of different materials.The influence of proton incident energy and GTV material on the annihilation photon distribution is discussed.In this paper,the concept of "annihilation photon peak" is proposed.Define the position of the annihilation photon flux decline maximum gradient of annihilation photons peak position.The results show that the position of the annihilation photon peak is almost the same asthe Bragg peak,the position deviation is less than 1 mm,and the positioning accuracy is high.This work provides the reference data for the study of the follow-up precision positioning while validating the feasibility of the new positioning method.