质子治疗中基于飞行时间的实时γ射线成像重建
A Time-Of-Flight-Based Reconstruction for Real-Time Prompt-Gamma Imaging in Protontherapy
摘要：
我们目前正在构思，通过（MC）模拟，多通道伽马探测器阵列（TIARA的飞行时间成像ARrAy）的质子治疗的在线监测。通过测量位于上游的束流监测器和质子-伽马（PG）探测器之间的飞行时间（TOF），我们的目标是重建PG顶点分布，以检测质子束输送的可能偏差。本文提出了两种非迭代重建策略。第一种方法是基于解析公式的解析度，该解析公式描述了PG顶点在3D中的分布。在这里，它是解决下的一维近似，以测量潜在的质子范围沿束方向的位移。第二种是基于TIARA像素探测器的重心（COG）计数的计算，并提供关于可能的光束位移的3D信息。在两种不同的情况下评价PG顶点重建。符合时间分辨率为100 ps（rms），可以达到在单质子制度（操作减少的束流），并使用外部束监视器提供一个启动触发的TOF测量。在这些条件下，MC模拟表明，毫米质子范围移位灵敏度可以实现在2 $σ$与10 $^{8}$入射质子。如果治疗不符合治疗计划，这种精度水平将允许实时采取行动。还考虑了1 ns（rms）TOF分辨率的最差情况，以证明可以通过增加采集统计来补偿退化的定时信息：在这种情况下，在2 $σ$和10个$^{9}$入射质子下可检测到2 mm距离偏移。COG方法已显示出优异的检测横向束位移的能力：在2 $σ$处发现2 mm的灵敏度与10个$^{8}$入射质子。
英文摘要：
We are currently conceiving, through (MC) simulation, a multi-channel gamma detector array (TIARA for Time-of-flight Imaging ARrAy) for the online monitoring of protontherapy treatments. By measuring the Time-Of-Flight (TOF) between a beam monitor placed upstream and the Prompt-Gamma (PG) detector, our goal is to reconstruct the PG vertex distribution to detect a possible deviation of proton beam delivery. In this paper, two non-iterative reconstruction strategies are proposed. The first is based on the resolution of an analytical formula describing the PG vertex distribution in 3D. Here, it was resolved under a one-dimensional approximation in order to measure a potential proton range shift along the beam direction. The second is based on the calculation of the Centre-Of-Gravity (COG) of the TIARA pixel detectors counts and also provides 3D information on a possible beam displacement. The PG vertex reconstruction was evaluated in two different scenarios. A coincidence time resolution of 100 ps (rms) can be attained in single proton regime (operating a reduction of the beam current) and using an external beam monitor to provide a start trigger for the TOF measurement. Under these conditions, MC simulations have shown that a millimetric proton range shift sensitivity can be achieved at 2$σ$ with 10$^{8}$ incident protons. This level of accuracy would allow to act in real-time if the treatment does not conform to treatment plan. A worst case scenario of a 1 ns (rms) TOF resolution was also considered to demonstrate that a degraded timing information can be compensated by increasing the acquisition statistics: in this case, a 2 mm range shift would be detectable at 2$σ$ with 10$^{9}$ incident protons. The COG method has shown excellent capabilities of detecting lateral beam displacements: a 2 mm sensitivity was found at 2$σ$ with 10$^{8}$ incident protons.
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