Fourkal E, Li J S, Ding M, Tajima T, Ma C M
Radiation Oncology Department, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA.
Med Phys. 2003 Jul;30(7):1660-70. doi: 10.1118/1.1586268.
In this paper we present calculations for the design of a particle selection system for laser-accelerated proton therapy. Laser-accelerated protons coming from a thin high-density foil have broad energy and angular spectra leading to dose distributions that cannot be directly used for therapeutic applications. Our solution to this problem is a compact particle selection and collimation device that delivers small pencil beams of protons with desired energy spectra. We propose a spectrometer-like particle selection and beam modulation system in which the magnetic field will be used to spread the protons spatially according to their energies and emitting angles. Subsequently, an aperture will be used to select the protons within a therapeutic window of energy (energy modulation). It will be shown that for the effective proton spatial differentiation, the primary collimation device should be used, which will collimate protons to the desired angular distribution and limit the spatial mixing of different energy protons once they have traveled through the magnetic system. Due to the angular proton distribution, the spatial mixing of protons of different energies will always be present and it will result in a proton energy spread with the width depending on the energy. For 250 MeV protons, the width (from the maximum to the minimum energy) is found to be 50 MeV for the magnetic field configuration used in our calculations. As the proton energy decreases, its energy width decreases as well, and for 80 MeV protons it equals 9 MeV. The presence of the energy width in the proton energy distribution will modify the depth dose curves needed for the energy modulation calculation. The matching magnetic field setup will ensure the refocusing of the selected protons and the final beam will be collimated by the secondary collimator. The calculations presented in this article show that the dose rate that the selection system can yield is on the order of D=260 Gy/min for a field size of 1 x 1 cm2.
在本文中，我们给出了用于激光加速质子治疗的粒子选择系统设计的计算结果。来自薄高密度箔的激光加速质子具有宽广的能量和角谱，导致剂量分布不能直接用于治疗应用。我们针对这个问题的解决方案是一种紧凑的粒子选择和准直装置，它能提供具有所需能谱的小质子笔形束。我们提出一种类似光谱仪的粒子选择和束调制系统，其中磁场将用于根据质子的能量和发射角度在空间上分散质子。随后，一个孔径将用于在能量治疗窗口内选择质子（能量调制）。结果表明，为了实现有效的质子空间区分，应使用初级准直装置，它将质子准直到所需的角分布，并在不同能量的质子穿过磁系统后限制它们的空间混合。由于质子的角分布，不同能量质子的空间混合将始终存在，这将导致质子能量展宽，其宽度取决于能量。对于250 MeV的质子，在我们计算中使用的磁场配置下，宽度（从最大能量到最小能量）为50 MeV。随着质子能量降低，其能量宽度也会减小，对于80 MeV的质子，其等于9 MeV。质子能量分布中能量宽度的存在将修改能量调制计算所需的深度剂量曲线。匹配的磁场设置将确保所选质子的重新聚焦，最终束将由次级准直器准直。本文给出的计算表明，对于1×1 cm2的射野尺寸，选择系统能够产生的剂量率约为D = 260 Gy/min。
