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快速获取碳离子束Bragg峰位的荧光探测器设计与验证

Design and Verification of Fluorescence Detector for Rapidly Acquiring the Bragg Peak Position of Carbon Ion Beam

  • 摘要: 提出了一种用于快速获取碳离子束在闪烁体材料中Bragg峰位置的荧光探测器方案。该方案基于闪烁体在碳离子束流照射下发出荧光的特性,使用CMOS相机在薄层闪烁体侧方获得荧光强度分布图像,通过对图像的分析快速得到碳离子束Bragg峰位在闪烁体材料中的位置。依据该方案研发了荧光探测器,在均匀照射野和笔形束两种照射条件下,利用该探测器对不同能量的碳离子束进行了实验测量。实验结果表明,可清晰地从探测器获得的荧光图像上观察到碳离子Bragg峰。同时,采用蒙特卡罗模拟方法对上述相同的实验条件设置进行了模拟计算。结果发现,荧光探测器测量的碳离子束在闪烁体材料中的Bragg峰位与蒙特卡罗模拟计算的结果由于模拟的条件和测量时探测器的实际设置不完全一致而出现一定的差异,但不同照射条件下的差异是基本一致的。因此,通过实验测量及蒙特卡罗模拟验证了本文方案的荧光探测器可用于快速获取碳离子束在闪烁体材料中的Bragg峰位,为建立一种基于荧光探测器进行碳离子放疗束流性能快速质量保证的测量方法打下了坚实的基础。

     

    Abstract: A design scheme of fluorescence detector was proposed for rapidly acquiring the Bragg peak position of carbon ion beam in scintillator material. Based on the characteristic of scintillator emitting fluorescence under the irradiation of carbon ion beam, CMOS camera is applied to acquire the image of fluorescent intensity distribution on the side of a thin scintillator, and then the Bragg peak position of carbon ion beam in the scintillator material is quickly obtained by analyzing the fluorescent image. According to the scheme, a fluorescence detector was developed and then used for experimental measurement under the irradiation of carbon-ion uniform fields and pencil beams with different energies. The experimental results showed that the Bragg peak position of the carbon ion beams could be clearly observed from the fluorescent image obtained by the detector. Moreover, the method of Monte Carlo simulation was used to calculate the depth dose distribution of carbon ion beams under the experimental conditions mentioned above. It was found that there was a penetration depth difference between the measured and calculated Bragg peak positions of carbon ion beam in the scintillator material by the fluorescence detector and the Monte Carlo simulation due to the difference between their settings, but the differences under the various irradiation conditions were nearly the same. Therefore, the experimental measurements and Monte Carlo simulations verified that the fluorescence detector scheme could be used for quickly acquiring the Bragg peak position of carbon ion beam in the scintillator material definitely, which provides a substantial basis for establishing a fast fluorescence detector-based quality assurance measurement method in carbon ion radiotherapy.

     

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