Luo Wei, Fourkal Eugene, Li Jinsheng, Ma Chang-Ming
Department of Radiation Oncology, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA.
Med Phys. 2005 Mar;32(3):794-806. doi: 10.1118/1.1861772.
In a laser-accelerated proton therapy system, the initial protons have broad energy and angular distributions, which are not suitable for direct therapeutic applications. A compact particle selection and collimation device is needed to deliver small pencil beams of protons with desired energy spectra. In this work, we characterize a superconducting magnet system that produces a desired magnetic field configuration to spread the protons with different energies and emitting angles for particle selection. Four magnets are set side by side along the beam axis; each is made of NbTi wires which carry a current density of approximately 10(5) A/cm2 at 4.2 K, and produces a magnetic field of approximately 4.4 T in the corresponding region. Collimation is applied to both the entrance and the exit of the particle selection system to generate a desired proton pencil beam. In the middle of the magnet system, where the magnetic field is close to zero, a particle selection collimator allows only the protons with desired energies to pass through for therapy. Simulations of proton transport in the presence of the magnetic field show that the selected protons have successfully refocused on the beam axis after passing through the magnetic field with the optimal magnet system. The energy spread for any given characteristic proton energy has been obtained. It is shown that the energy spread is a function of the magnetic field strength and collimator size and reaches the full width at half maximum of 25 MeV for 230 MeV protons. Dose distributions have also been calculated with the GEANT3 Monte Carlo code to study the dosimetric properties of the laser-accelerated proton beams for radiation therapy applications.
在激光加速质子治疗系统中，初始质子具有较宽的能量和角度分布，不适合直接用于治疗。需要一种紧凑的粒子选择和准直装置来输送具有所需能谱的小质子笔形束。在这项工作中，我们对一个超导磁体系统进行了表征，该系统产生所需的磁场配置，以分散具有不同能量和发射角度的质子用于粒子选择。四个磁体沿束轴并排设置；每个磁体由铌钛丝制成，在4.2 K时承载约10(5) A/cm2的电流密度，并在相应区域产生约4.4 T的磁场。在粒子选择系统的入口和出口都进行准直，以产生所需的质子笔形束。在磁体系统的中间，磁场接近零的地方，一个粒子选择准直器只允许具有所需能量的质子通过用于治疗。在存在磁场的情况下对质子传输进行的模拟表明，在通过具有最佳磁体系统的磁场后，所选质子已成功重新聚焦在束轴上。已获得任何给定特征质子能量的能量展宽。结果表明，能量展宽是磁场强度和准直器尺寸的函数，对于230 MeV质子，半高宽达到25 MeV。还使用GEANT3蒙特卡罗代码计算了剂量分布，以研究用于放射治疗应用的激光加速质子束的剂量学特性。
