使用瞬发gamma-ray光谱学进行质子射程验证的全尺寸临床原型
A full-scale clinical prototype for proton range verification using prompt gamma-ray spectroscopy
摘要：
我们提出了一个全尺寸的临床原型系统，在体内范围验证的质子束，使用即时伽玛射线光谱法。探测系统由八个LaBr3吸收器和一个钨准直器组成，安装在一个旋转框架上。定制的电子和校准算法已被开发用于测量的能量和时间分辨的伽玛射线光谱在质子照射在临床剂量率。使用实验确定的核反应截面和GPU加速的蒙特卡罗模拟，为每个单独的伽马射线束创建预期的伽马射线发射的详细模型。通过最小化测量和该模型之间的差异来确定质子束的绝对范围，留下束的绝对范围和被照射物质的元素浓度作为自由参数。该系统的特点是在一个类似临床的情况下，通过照射不同的phantomes与扫描的准直光束。将0.9 Gy的剂量输送至5 x 10 x 10 cm $^3$靶，射束电流2 nA入射到体模上。使用不同的范围移位器和材料来测试验证方法的稳健性并计算检测范围的准确度。当在10 mm半径和10 mm深度的圆柱形区域内聚集质子束点时，确定远端能量层每个点的绝对质子范围，平均统计精度为1.1 mm，置信水平为95%，平均系统偏差为0.5 mm。我们引入的小范围误差被成功地检测到，即使元素组成的大差异也不会影响范围验证的准确性。这些结果表明，我们的系统适用于我们即将进行的临床研究中患者治疗期间的范围验证。
英文摘要：
We present a full-scale clinical prototype system for in vivo range verification of proton pencil-beams using the prompt gamma-ray spectroscopy method. The detection system consists of eight LaBr3 scintillators and a tungsten collimator, mounted on a rotating frame. Custom electronics and calibration algorithms have been developed for the measurement of energy- and time-resolved gamma-ray spectra during proton irradiation at a clinical dose rate. Using experimentally determined nuclear reaction cross sections and a GPU-accelerated Monte Carlo simulation, a detailed model of the expected gamma-ray emissions is created for each individual pencil-beam. The absolute range of the proton pencil-beams is determined by minimizing the discrepancy between the measurement and this model, leaving the absolute range of the beam and the elemental concentrations of the irradiated matter as free parameters. The system was characterized in a clinical-like situation by irradiating different phantoms with a scanning pencil-beam. A dose of 0.9 Gy was delivered to a 5x10x10 cm$^3$ target with a beam current of 2 nA incident on the phantom. Different range shifters and materials were used to test the robustness of the verification method and to calculate the accuracy of the detected range. The absolute proton range was determined for each spot of the distal energy layer with a mean statistical precision of 1.1 mm at a 95% confidence level and a mean systematic deviation of 0.5 mm, when aggregating pencil-beam spots within a cylindrical region of 10 mm radius and 10 mm depth. Small range errors that we introduced were successfully detected and even large differences in the elemental composition do not affect the range verification accuracy. These results show that our system is suitable for range verification during patient treatments in our upcoming clinical study.
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