Birgani Mohammad Javad Tahmasebi, Chegeni Nahid, Zabihzadeh Mansour, Tahmasbi Marziyeh
Ph.D., Professor, Department of Radiation Therapy, Golestan Hospital, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran.
Ph.D., Assistant Professor, Department of Medical Physics, Faculty of Medicine, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran.
Electron Physician. 2017 Dec 25;9(12):5932-5939. doi: 10.19082/5932. eCollection 2017 Dec.
Integrated proton therapy - MRI systems are capable of delivering high doses to the target tissues near sensitive organs and achieve better therapeutic results; however, the applied magnetic field for imaging, influences the protons path, changes the penetration depth and deflects the particles, laterally, leading to dose distribution variations.
To determine the effects of a magnetic field on the range and the lateral deflection of protons, analytically.
An analytical survey based on protons energy and range power law relation, without using small angle assumption was done. The penetration depth and lateral deflection of protons with therapeutic energy ranges 60-250 MeV in the presence of uniform magnetic fields of 0-10T intensities, were calculated analytically. Calculations were done for relativistic conditions with Mathematica software version 7.0, and MATLAB 7.0 was applied to plot curves and curve fittings.
In the presence of a magnetic field, the depth of Bragg peak was decreased and it was shifted laterally. A second order polynomial model with power equation for its coefficients and a power model with quadratic polynomial coefficients predicted the maximum lateral deflection (y) and maximum penetration depth (z) variations with energy and magnetic field intensity, respectively.
The applied correction for deflection angle will give more reliable results in initial energy of 250 MeV and 3T magnetic field intensity. For lower energies and magnetic field intensities the differences are negligible, clinically.
集成质子治疗 - 磁共振成像系统能够向敏感器官附近的靶组织输送高剂量辐射，并取得更好的治疗效果；然而，用于成像的外加磁场会影响质子路径，改变穿透深度，并使粒子横向偏转，从而导致剂量分布变化。
通过分析确定磁场对质子射程和横向偏转的影响。
基于质子能量和射程幂律关系进行分析研究，不采用小角度假设。分析计算了在强度为0 - 10T的均匀磁场中，治疗能量范围为60 - 250MeV的质子的穿透深度和横向偏转。使用Mathematica软件7.0版本在相对论条件下进行计算，并应用MATLAB 7.0绘制曲线和进行曲线拟合。
在存在磁场的情况下，布拉格峰深度减小并横向移动。系数为幂方程的二阶多项式模型和系数为二次多项式的幂模型分别预测了最大横向偏转（y）和最大穿透深度（z）随能量和磁场强度的变化。
在初始能量为250MeV和磁场强度为3T时，应用偏转角校正将得到更可靠的结果。对于较低能量和磁场强度，临床上差异可忽略不计。
