Development of array-type prompt gamma measurement system for in vivo range verification in proton therapy
Development of array-type prompt gamma measurement system for in vivo range verification in proton therapy
复制标题
DOI：
10.1118/1.3694098
复制
发表时间：
2012-04-01
期刊：
影响因子：
3.8
通讯作者：
Lee, Se Byeong
中科院分区：
文献类型：
--
作者：
Min, Chul Hee;Lee, Han Rim;Lee, Se Byeong
目的：体内射程验证是质子治疗中最重要的部分之一，目的是充分利用质子治疗向肿瘤提供高剂量辐射的优点，同时避免正常组织出现所谓的Bragg峰。然而，目前范围验证方法还没有在临床上使用。为优化和评估阵列式瞬发伽马测量系统的结构，以确定质子治疗活体射程验证的远距离剂量边缘。方法：为了有效地测量瞬发伽马，利用MCNPX程序对测量系统进行了蒙特卡罗模拟，优化了测量系统的结构，并用蒙特卡罗方法了解了本底伽马(主要是中子俘获伽马)对测量伽马分布的影响。为了降低本底伽马的影响，在测量瞬发伽马时，采用了4-10 MeV的最佳能量窗。在优化研究中使用了参数化源来最大限度地提高计算速度。建立了一种简化的测试测量系统，只使用一个探测器从一个测量位置移动到另一个测量位置，并将其应用于80-220 MeV的治疗质子束。为了准确确定远端剂量边缘，将S型曲线拟合法应用于测量的瞬发伽玛分布，然后将曲线拟合中最大值和最小值之间的半值的位置确定为远端剂量边缘，并与由质子剂量分布评估的束流范围进行比较。结果：优化过程中采用的参数化源项使计算速度提高了近300倍。优化研究表明，采用3 mm、2 mm、2 mm和150 mm的阵列式闪烁体厚度、狭缝宽度、间隔厚度和狭缝长度的测量系统，可以有效地测量瞬变伽马分布，使背景伽马的贡献最小化。结果表明，对于类似于4nA的质子束，在每个测量位置测量10个S，可以很容易地获得几百个瞬发伽马计数。对于5.17(80 MeV)、14.99(150 MeV)和27.38(220 MeV)cm的质子束，由瞬发伽马分布确定的远端剂量边缘分别为5.45、14.73和27.74 cm。结论：阵列式测量系统可以在短时间内测量治疗性质子束的瞬发伽马分布，并且不需要任何复杂的分析就可以确定远端剂量边缘，误差在几毫米以内。(C)2012年美国医学物理学家协会。[http://dx.doi.org/10.1118/1.3694098]
Purpose: In vivo range verification is one of the most important parts of proton therapy to fully utilize its benefits delivering high radiation dose to tumor, while sparing the normal tissue with the so-called Bragg peak. Currently, however, range verification method is not used in clinics. The purpose of the present study is to optimize and evaluate the configuration of an array-type prompt gamma measurement system on determining distal dose edge for in vivo range verification of proton therapy.Methods: To effectively measure the prompt gammas against the background gammas, the Monte Carlo simulations with the MCNPX code were employed in optimizing the configuration of the measurement system, and the Monte Carlo method was also used to understand the effect of the background gammas, mainly neutron capture gammas, in the measured gamma distribution. To reduce the effect of the background gammas, the optimized energy window of 4-10 MeV in measuring the prompt gammas was employed. A parameterized source was used to maximize computation speed in the optimization study. A simplified test measurement system, using only one detector moving from one measurement location to the next, was constructed and applied to therapeutic proton beams of 80-220 MeV. For accurate determination of the distal dose edge, the sigmoidal curve-fitting method was applied to the measured distributions of the prompt gammas, and then, the location of the half-value between the maximum and minimum value in the curve-fitting was determined as the distal dose edge and compared with the beam range assessed by the proton dose distribution.Results: The parameterized source term employed in optimization process improved the calculation speed by up to similar to 300 times. The optimization study indicates that an array-type measurement system with 3, 2, 2, and 150 mm for scintillator thickness, slit width, septal thickness, and slit length, respectively, can effectively measure the prompt gamma distributions minimizing the contribution of background gammas. The present results show that a few hundred counts of prompt gammas can be easily obtained by measuring 10 s at each measurement location for proton beams of similar to 4 nA. The distal dose edges determined by the prompt gamma distribution are 5.45, 14.73, and 27.74 cm for proton beams of 5.17 (80 MeV), 14.99 (150 MeV), and 27.38 (220 MeV) cm, respectively.Conclusions: The results show that the array-type measurement system can measure prompt gamma distributions from a therapeutic proton beam within a short measurement time, and that the distal dose edge can be determined within a few millimeters of error without using any sophisticated analysis. (C) 2012 American Association of Physicists in Medicine. [http://dx.doi.org/10.1118/1.3694098]