Characterizing the response of miniature scintillation detectors when irradiated with proton beams
Characterizing the response of miniature scintillation detectors when irradiated with proton beams
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DOI：
10.1088/0031-9155/53/7/004
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发表时间：
2008-04-07
影响因子：
3.5
通讯作者：
Beddar, Sam
中科院分区：
文献类型：
--
作者：
Archambault, Louis;Polf, Jerimy C.;Beddar, Sam
设计用于质子放射治疗的塑料闪烁探测器需要仔细考虑。如果足够小，大多数塑料闪烁体不会干扰质子束，但由于猝灭效应可能会表现出一些能量依赖性。在这项工作中，我们研究了影响这种闪烁探测器性能的因素。利用蒙特卡罗模拟方法研究了能量在50 ~ 250 MeV之间的质子束的信号振幅、水等效性、空间分辨率和光输出的猝灭。在蒙特卡罗模拟中实现了淬火效应，并与先前的实验数据进行了比较，以验证其有效性。在质子剂量率为100 cGy min（-1）的情况下，塑料闪烁光纤探测器的信号幅值约为300光子/ MeV，相当于30 pW的功率。有了反射涂层后，信号幅度可增加2倍。我们还发现切伦科夫光并不是一个重要的噪声源。对于能量高于50 MeV的质子，在整个深度-剂量曲线上，塑料闪烁体中沉积的剂量小于相同体积水中沉积的剂量的2%。一个半径为0.5mm的闪烁探测器提供了足够的空间分辨率，用于100 MeV或更高的质子束。塑料闪烁体在质子照射时的主要缺点是猝灭效应，这减少了闪烁量，导致150 MeV或更高的光束在布拉格峰处的剂量低估接近30%。然而，在考虑所有质子能量的深度-剂量曲线的近半部分，猝灭水平几乎是恒定的。因此，我们得出结论，有可能构建一个有效的探测器，以克服传统上在质子剂量测定中遇到的问题。闪烁探测器可用于表面或浅层测量，只需对特定光束能量进行一次校准。对于更深的测量，蒙特卡罗模拟可以用来产生与深度相关的校正因子。
Designing a plastic scintillation detector for proton radiation therapy requires careful consideration. Most of the plastic scintillators should not perturb a proton beam if they are sufficiently small but may exhibit some energy dependence due to the quenching effect. In this work, we studied the factors that would affect the performance of such scintillation detectors. We performed Monte Carlo simulations of proton beams with energies between 50 and 250 MeV to study signal amplitude, water equivalence, spatial resolution and quenching of light output. Implementation of the quenching effect in the Monte Carlo simulations was then compared with prior experimental data for validation. The signal amplitude of a plastic scintillating fiber detector was on the order of 300 photons per MeV of energy deposited in the detector, corresponding to a power of about 30 pW at a proton dose rate of 100 cGy min(-1). The signal amplitude could be increased by up to a factor of 2 with reflective coating. We also found that Cerenkov light was not a significant source of noise. Dose deposited in the plastic scintillator was within 2% of the dose deposited in a similar volume of water throughout the whole depth-dose curve for protons with energies higher than 50 MeV. A scintillation detector with a radius of 0.5mm offers a sufficient spatial resolution for use with a proton beam of 100 MeV or more. The main disadvantage of plastic scintillators when irradiated by protons was the quenching effect, which reduced the amount of scintillation and resulted in dose underestimation by close to 30% at the Bragg peak for beams of 150 MeV or more. However, the level of quenching was nearly constant throughout the proximal half of the depth - dose curve for all proton energies considered. We therefore conclude that it is possible to construct an effective detector to overcome the problems traditionally encountered in proton dosimetry. Scintillation detectors could be used for surface or shallow measurements with a single calibration for specific beam energy. For deeper measurements, Monte Carlo simulations can be used to generate depth-dependent correction factors.