磁场中加速器小野X线射束在非均匀模体中的剂量沉积特性研究  

Study on Dose Deposited Characteristics of Small-Field X-Ray Beam from Accelerator in Heterogeneous Phantom Under Magnetic Field

作　　者：何奕松 余行 傅玉川[2] 邹炼[1] HE Yisong;YU Hang;FU Yuchuan;ZOU Lian(Center of Cancer,Sichuan Provincial People’s Hospital,Chengdu Sichuan 610072,China;Center of Radiotherapy Physics&Technology,West China Hospital of Sichuan University,Chengdu Sichuan 610041,China)

机构地区：[1]四川省人民医院肿瘤中心,四川成都610072 [2]四川大学华西医院放射物理技术中心,四川成都610041

出　　处：《中国医疗设备》2024年第5期48-54,共7页China Medical Devices

摘　　要：目的利用蒙特卡洛模拟方法研究磁场中加速器输出的小野X线射束在非均匀模体中的剂量沉积特性。方法使用通用蒙卡程序EGSnrc并结合Varian官方提供的相空间文件搭建TrueBeam 6 MV机头模型,在源皮距为100 cm处分别模拟10 cm×10 cm的常规野和2 cm×2 cm的小野。先模拟常规野在均匀水模体中的能量沉积以验证模型的正确性,再模拟小野分别在非均匀的水-肺-水模体和水-骨-水模体中的能量沉积,在空间中添加与射束方向正交的1.5 T静态磁场后再进行模拟,最后分析剂量沉积特性。结果常规野的结果显示,无磁场时,Dmax深度为1.5 cm;磁场存在时,建成区缩短且Dmax深度前移至1.1 cm。小野的结果显示,磁场的存在导致原本的剂量沉积特性反转:水-肺-水模体中,两个交界面处分别有36.92%和-36.44%的剂量改变;水-骨-水模体中,两个交界面处分别有-11.17%和10.89%的剂量改变。结论磁场的存在会使加速器输出的小野射束在模体中的剂量沉积情况发生较大程度改变,特别是在非均匀介质的交界处。Objective To investigate the dose deposited characteristics of small-field X-ray beam generated by accelerator in heterogeneous phantom under magnetic field using Monte Carlo simulation method.Methods A TrueBeam 6 MV head model was constructed using EGSnrc combined with phase space file provided by Varian’s official.Simulations were performed at a sourceto-skin distance of 100 cm for both a routine-field of 10 cm×10 cm and a small-field of 2 cm×2 cm.First,the energy deposition of the routine-field was simulated in homogeneous water phantom to validate the model’s accuracy.Then,the energy deposition of the small-field was simulated in heterogeneous water-lung-water and water-bone-water phantoms.A 1.5 T static magnetic field orthogonal to the beam direction was added to the spatial setup before conducting the simulations.Finally,the dose deposition characteristics were analyzed.Results The results for the routine-field showed that without a magnetic field,the depth of Dmax was 1.5 cm;the built-up area was shortened and the depth of Dmax shifted forward to 1.1 cm in the presence of magnetic field.The results for the small-field showed that the presence of magnetic field would lead to a reversal in the dose deposited characteristics.There was a dose change of 36.92%and-36.44%at the two interface regions in the water-lung-water phantom,and there was a dose change of-11.17%and 10.89%at the two interface regions in the water-bone-water phantom.Conclusion The presence of magnetic field can cause significant changes in the dose deposition of the small-field beam generated by the accelerator within the phantom,especially at the junction of heterogeneous mediums.

关 键 词：蒙特卡洛模拟 磁场 小野射束 非均匀模体 剂量沉积特性 

分 类 号：R144[医药卫生—公共卫生与预防医学]