基于磁场调制的质子放疗新方法及其调制机制

摘要

This study proposes a novel magnetic-modulated proton therapy,explores tumor and organ doses as functions of the magnetic modulation method,and investigates the application of the magnetic-modulated therapy in curing organ-surrounded tumors.Based on Geant4 Monte Carlo code,we constructed an ideal organ-surrounded structure and an abdominal structure comprising a pancreatic tumor.Bragg peak positions of proton beams were modulated through altering the strengths and directions of the magnetic fields inside the two geometric structures.Following the magnetic-deflected transportation tracks,the proton beams were modulated to bypass the vital organs and irradiate the tumor.For the ideal organ-surrounding configuration,the tumor can be sufficiently covered by 95 ％ relative doses,and the vital organ volume receiving proton irradiations can be controlled to nearly zero.For the abdominal structure comprising the pancreatic tumor,the proton beams modulated by magnetic fields can bypass the spinal cord and left kidney and irradiate the pancreatic tumor.Sufficient coverage of 95 ％ relative doses can be achieved through the magnetic-modulated proton therapy method.%提出一种基于磁场调制的质子放射治疗新方法,探索肿瘤剂量、正常器官剂量与磁场调制方法之间的关联机制,研究磁场调制质子放疗在器官环绕型肿瘤(肿瘤被正常器官环绕或包围)治疗中的应用.基于蒙特卡罗粒子输运程序Geant4,分别建立了理想器官环绕结构(由若干平行六面体结构组成)和含胰腺肿瘤人体腹部解剖结构两种几何构型.分别对两种几何构型内部施加磁场,通过改变磁场强度和方向,调制质子束布拉格峰几何位置,利用质子径迹的磁致偏转效应使质子束绕开正常器官对肿瘤进行照射.对于理想器官环绕型构型,磁场调制质子放疗可在保证95％剂量覆盖肿瘤情况下将受质子照射正常器官体积控制在接近于零的极低水平.对于胰腺肿瘤解剖构型,磁场调制方法可使质子束在调制磁场作用下,绕过脊髓和肾脏照射肿瘤,并使肿瘤被95％剂量较好地覆盖.通过磁场调制,可对质子束布拉格峰几何位置和质子径迹弯曲程度进行调制,绕过正常器官对肿瘤进行照射,从而最大限度地减少正常器官的受照体积和剂量.