Development of a storage phosphor imaging system for proton pencil beam spot profile determination.
Development of a storage phosphor imaging system for proton pencil beam spot profile determination.
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用于质子铅笔束光斑轮廓测量的存储荧光粉成像系统的研制。
作者：
精确的亚毫米精度的二维(2D)轮廓测量对于质子束调试和定期质量保证(QA)是必要的，目前在我们机构使用商用闪烁探测器(Lynx PT)进行，独立检查的手段有限。这项工作的目的是创建一个由内部光学扫描仪和BaFBrI：Eu2+存储荧光粉剂量计组成的独立剂量测量系统，方法是：(A)确定光学扫描仪的最佳设置，(B)用存储荧光粉测量2D质子点轮廓，以及(C)将它们与使用商用闪烁探测器的类似测量结果进行比较。建立了室内二维实验室光学扫描仪，并对其进行了空间校准，以实现精确的二维光激励发光(PSL)剂量测量。用线扫描均匀照射正方形5×5cm2 BaFBrI：Eu2+剂量计样品，以确定物理和电子扫描仪设置，从而在亚毫米空间分辨率下产生最高的信噪比(SNR)。然后通过测量(A)标准X射线铅条体模上的线对和(B)调制传递函数来定量地评估扫描仪的最终空间分辨率。随后，在最大能量(E0=227.1 MeV)下，在1、10、20、30、40和50个监测单元(MU)设置下获得了来自Mevion S250i Hyperscan质子单元的2D质子斑点轮廓，并与商业闪烁探测器的基线轮廓进行了比较，在参考条件下，1 MU被校准为提供1GY绝对质子剂量-水，也就是说，在10×10平方厘米的视野大小中，在等中心5厘米深的水中，以最大能量(227.1 MeV)均匀分布的41×41个质子斑点。剂量学系统对(A)±1 mm的位置漂移和±0.3 mm的束流横向扩展变化的灵敏度通过对相应的人工移位的光束轮廓的交叉线和内联图进行高斯拟合来定量评估。(A)Δτ=数据样本之间的时间间隔，(B)Vx=1.235 cm/S扫描速度，(C)1%激光透射率(0.02 mW功率)和(D)(Δx，Δy)=(0.33，0.5 mm)像素大小的物理扫描仪设置，其中电子设置为(A)300ms时间常数，(B)正常动态储备，(C)24db/OCT低通滤波斜率，(D)160 Hz斩波频率，在保持亚毫米空间分辨率的同时产生最高的SNR。BaFBr0.85I0.15：Eu2+储存磷光体剂量计在1-50MU范围内呈线性关系，其分布在150MU以下不饱和。该扫描仪能够检测到交叉线和直线方向上±1 mm的横向位移，以及通过改变入射质子能量而人为引入的±0.3 mm束散度变化。具体到我们的质子装置，也可以通过束流扩展测量间接探测到±1 MeV的质子能量变化。我们的组合剂量测量系统包括内部实验室光学扫描仪和可重复使用的BaFBr0.85I0.15：Eu2+存储荧光粉，展示了足够的空间分辨率和剂量测量精度，支持将其用作独立的质子点测量剂量计系统。它的宽动态范围允许其他多用途的应用，如质子晕测量。
Accurate two-dimensional (2D) profile measurements at submillimeter precision are necessary for proton beam commissioning and periodic quality assurance (QA) purposes and are currently performed at our institution with a commercial scintillation detector (Lynx PT) with limited means for independent checks. The purpose of this work was to create an independent dosimetry system consisting of an in-house optical scanner and a BaFBrI:Eu2+ storage phosphor dosimeter by: (a) determining the optimal settings for the optical scanner, (b) measuring 2D proton spot profiles with the storage phosphors, and (c) comparing them to similar measurements using a commercial scintillation detector. An in-house 2D laboratory optical scanner was constructed and spatially calibrated for accurate 2D photostimulated luminescence (PSL) dosimetry. Square 5 × 5 cm2 BaFBrI:Eu2+ dosimeter samples were uniformly irradiated with line scans performed to determine the physical and electronic scanner settings resulting in the highest signal-to-noise ratios (SNR) at a sub-millimeter spatial resolution. The resultant spatial resolution of the scanner was then quantitatively assessed by measuring (a) line pairs on a standard X-ray lead bar phantom and (b) modulation transfer functions. Following this, 2D proton spot profiles from a Mevion S250i Hyperscan proton unit were obtained at 1, 10, 20, 30, 40, and 50 monitor unit (MU) settings at maximum energy (E0 = 227.1 MeV) and compared to baseline profiles from a commercial scintillation detector, where 1 MU is calibrated to deliver 1 Gy absolute proton dose-to-water under reference conditions, that is, 41 × 41 proton spots uniformly spaced by 0.25 cm within a 10 × 10 cm2 square field size at maximum energy (227.1 MeV) in water at depth of 5 cm at isocenter. The dosimetric system’s sensitivities to (a) ±1 mm positional shifts and ±0.3 mm beam lateral spread changes were quantitatively evaluated through a Gaussian fitting of the crossline and inline plots of the respective artificially shifted beam profiles. The physical scanner settings of (a) Δτ = 27 ms time interval between data samples, (b) vx = 1.235 cm/s scanning speed, (c) 1% laser transmission (0.02 mW power) and (d) (Δx, Δy) = (0.33, 0.50 mm) pixel sizes with electronic settings of (a) 300 microseconds time constant, (b) normal dynamic reserve, (c) 24 dB/oct low pass filter slope, and (d) 160 Hz chopping frequency resulted in the highest SNR while maintaining sub-millimeter spatial resolution. The BaFBr0.85I0.15:Eu2+ storage phosphor dosimeters were linear from 1 to 50 MU and their profiles did not saturate up to 150 MU. The scanner was able to detect lateral displacements of ±1 mm in both the crossline and inline directions and ±0.3 mm beam spread changes that were artificially introduced by varying the incident proton energy. Specific to our proton unit, proton energy changes of ±1 MeV can also be detected indirectly via beam spread measurements. Our combined dosimetric system including an in-house laboratory optical scanner and reusable BaFBr0.85I0.15:Eu2+ storage phosphors demonstrated a sufficient spatial resolution and dosimetric accuracy to support its use as an independent proton spot measurement dosimeter system. Its wide dynamic range allows for other versatile applications such as proton halo measurements.
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影响因子：
3.8
作者：
Setianegara J;Mazur TR;Yang D;Li HH
通讯作者：
Li HH
DOI：
10.1016/s0360-3016(01)02826-7
发表时间：
2002-05-01
影响因子：
7
作者：
Schneider, U;Agosteo, S;Besserer, J
通讯作者：
Besserer, J
影响因子：
1.9
作者：
LI, YJ;KATZ, J
通讯作者：
KATZ, J
影响因子：
3.5
作者：
Lin, Liyong;Ainsley, Christopher G.;McDonough, James E.
通讯作者：
McDonough, James E.
影响因子：
3.8
作者：
Setianegara, Jufri;Mazur, Thomas R.;Li, H. Harold
通讯作者：
Li, H. Harold