Department of Radiation Oncology, Harvard Medical School and Massachusetts General Hospital, Boston, MA 02114, USA. School of Medical Physics and Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands.
Phys Med Biol. 2013 Oct 21;58(20):L37-49. doi: 10.1088/0031-9155/58/20/L37. Epub 2013 Sep 27.
In this work, we present experimental results of a novel prompt gamma-ray detector for proton beam range verification. The detection system features an actively shielded cerium-doped lanthanum(III) bromide scintillator, coupled to a digital data acquisition system. The acquisition was synchronized to the cyclotron radio frequency to separate the prompt gamma-ray signals from the later-arriving neutron-induced background. We designed the detector to provide a high energy resolution and an effective reduction of background events, enabling discrete proton-induced prompt gamma lines to be resolved. Measuring discrete prompt gamma lines has several benefits for range verification. As the discrete energies correspond to specific nuclear transitions, the magnitudes of the different gamma lines have unique correlations with the proton energy and can be directly related to nuclear reaction cross sections. The quantification of discrete gamma lines also enables elemental analysis of tissue in the beam path, providing a better prediction of prompt gamma-ray yields. We present the results of experiments in which a water phantom was irradiated with proton pencil-beams in a clinical proton therapy gantry. A slit collimator was used to collimate the prompt gamma-rays, and measurements were performed at 27 positions along the path of proton beams with ranges of 9, 16 and 23 g cm(-2) in water. The magnitudes of discrete gamma lines at 4.44, 5.2 and 6.13 MeV were quantified. The prompt gamma lines were found to be clearly resolved in dimensions of energy and time, and had a reproducible correlation with the proton depth-dose curve. We conclude that the measurement of discrete prompt gamma-rays for in vivo range verification of clinical proton beams is feasible, and plan to further study methods and detector designs for clinical use.
在这项工作中，我们展示了一种用于质子束射程验证的新型瞬发伽马射线探测器的实验结果。该探测系统采用主动屏蔽的掺铈镧（III）溴化物闪烁体，与数字数据采集系统耦合。采集与回旋加速器射频同步，以将瞬发伽马射线信号与随后到达的中子诱发背景区分开来。我们设计了该探测器，以提供高能量分辨率和有效减少背景事件，从而能够分辨离散的质子诱发瞬发伽马线。测量离散的瞬发伽马线对射程验证有几个好处。由于离散能量对应于特定的核跃迁，不同伽马线的幅度与质子能量具有独特的相关性，可以直接与核反应截面相关联。离散伽马线的定量分析还可以对束路径中的组织进行元素分析，从而更好地预测瞬发伽马射线的产额。我们介绍了在临床质子治疗旋转机架中用质子铅笔束辐照水模体的实验结果。使用狭缝准直器准直瞬发伽马射线，并在质子束路径上的 27 个位置进行测量，质子束射程在水中分别为 9、16 和 23 g cm(-2)。定量测量了 4.44、5.2 和 6.13 MeV 的离散伽马线。发现瞬发伽马线在能量和时间维度上清晰可辨，与质子深度剂量曲线具有可重复的相关性。我们得出结论，用于临床质子束体内射程验证的离散瞬发伽马射线的测量是可行的，并计划进一步研究用于临床的方法和探测器设计。
