一种使用有机闪烁体实时测量质子治疗中线性能量传递和剂量的方法。
A real-time method to simultaneously measure linear energy transfer and dose for proton therapy using organic scintillators.
机构信息
Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, 77030, USA.
The University of Texas Graduate School of Biomedical Sciences at Houston, Houston, TX, 77030, USA.
出版信息
Med Phys. 2018 Apr;45(4):1782-1789. doi: 10.1002/mp.12815. Epub 2018 Mar 7.
PURPOSE
Currently, no detectors are capable of simultaneously measuring dose and linear energy transfer (LET) in real time. In this study, we evaluated the feasibility of exploiting the difference in the response of various organic plastic scintillation detectors to measure LET and dose in therapeutic proton beams. The hypothesis behind this work was that the ratio of the responses of different scintillators exposed to the same proton beam can be used to obtain a LET vs ratio calibration curve that can then be used to infer LET under any other measurement conditions.
METHODS
We first used similar scintillators with different ionization quenching factors. LET values for different irradiation conditions were calculated using a validated Monte Carlo model of the proton beam line. The quenching factors in the Birks equation for different scintillators as a function of LET were obtained from measurements in a 100-MeV pristine proton beam. We then used four different organic scintillation materials - polystyrene (BCF-12), poly (methyl methacrylate), polyvinyltoluene, and a liquid scintillator - for which the LET response varied with regard to not only quenching but also differences in material density and relative stopping power. We simultaneously exposed the four different organic scintillators and a plane-parallel ion chamber to passively scattered proton beams at fluence-averaged LET. Comparisons to the expected values obtained from the Monte Carlo simulations were made on the basis of both dose and LET.
RESULTS
The maximum difference in the quenching factor was 20%, resulting in a 5% change in LET with a response ratio over a range of 5 keV/μm. Among all the scintillators investigated, the ratio of PMMA to BCF-12 provided the best correlation with LET values and was therefore used to construct the LET calibration curve. The expected LET values in the validation set were within 2% ± 6%, which resulted in dose accuracy of 1.5% ± 5.8% for the range of LET values investigated in this work.
CONCLUSIONS
We demonstrated the feasibility of using the ratio of the light outputs of two organic scintillators to simultaneously measure LET and dose in therapeutic proton beams for fluence-averaged LET values from 0.47 to 1.26 keV/μm. Further studies are needed to verify the response for higher LET values and the reproducibility of this method.
目的
目前，没有任何探测器能够实时地同时测量剂量和线性能量传递（LET）。在这项研究中，我们评估了利用各种有机塑料闪烁探测器对响应的差异来测量治疗质子束中的 LET 和剂量的可行性。这项工作背后的假设是，暴露于相同质子束的不同闪烁体的响应比可以用于获得 LET 与比值校准曲线，然后可以在任何其他测量条件下推断 LET。
方法
我们首先使用具有不同电离猝灭因子的类似闪烁体。使用质子束线的经过验证的蒙特卡罗模型计算了不同照射条件下的 LET 值。不同闪烁体的 Birks 方程中的猝灭因子作为 LET 的函数，是从 100 MeV 原始质子束的测量中获得的。然后，我们使用了四种不同的有机闪烁材料 - 聚苯乙烯（BCF-12）、聚甲基丙烯酸甲酯、聚氯乙烯和一种液体闪烁体 - 它们的 LET 响应不仅取决于猝灭，还取决于材料密度和相对阻止能力的差异。我们同时将四种不同的有机闪烁体和一个平面平行离子室暴露于平均剂量 LET 的被动散射质子束下。基于剂量和 LET，对基于蒙特卡罗模拟获得的预期值进行了比较。
结果
猝灭因子的最大差异为 20%，导致响应比在 5 keV/μm 的范围内发生 5%的 LET 变化。在所研究的所有闪烁体中，PMMA 与 BCF-12 的比值与 LET 值提供了最佳相关性，因此用于构建 LET 校准曲线。验证集中的预期 LET 值在 2%±6%范围内，这导致在本工作研究的 LET 值范围内剂量精度为 1.5%±5.8%。
结论
我们证明了使用两种有机闪烁体的光输出比来同时测量治疗质子束中的 LET 和剂量的可行性，适用于 0.47 至 1.26 keV/μm 的平均剂量 LET 值。需要进一步的研究来验证更高 LET 值的响应和这种方法的重现性。
Zotero 插件