Monte Carlo simulations of the imaging performance of metal plate/phosphor screens used in radiotherapy
Monte Carlo simulations of the imaging performance of metal plate/phosphor screens used in radiotherapy
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DOI：
10.1118/1.598727
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发表时间：
1999-10-01
期刊：
影响因子：
3.8
通讯作者：
Dössel, O
中科院分区：
文献类型：
--
作者：
Kausch, C;Schreiber, B;Dössel, O
用蒙特卡罗模拟方法研究了用于放射治疗射野成像的金属板/荧光屏的成像性能。为此，计算了不同金属和荧光粉以及不同厚度的金属和荧光粉在一定空间分辨率范围内的调制传递函数、噪声功率谱和探测量子效率[DQE(F)]。用EGS4电子伽马簇射程序模拟了X射线与金属板/荧光屏的相互作用。通过模拟单个光学光子的散射和重吸收事件来模拟荧光粉中的光学输运。结果表明，原子序数较高的金属在使DQE(F)最大化方面表现得比较轻的金属好。结果还表明，仅金属板/荧光屏的DQE(F)几乎是空间频率为0.4周/毫米的X射线量子吸收。此外，由于光学链条(反射镜、透镜和摄像机)对光学光子的二次量子吸收，导致空间频率的信噪比显著下降，而空间频率是门户图像成功配准的关键。因此，结论是，将光学链替换为直接放置在荧光粉下面的光电二极管的平面阵列将导致入射图像的图像质量的实质性改善。(C)1999年美国物理学家医学协会。[S0094-2405(99)01710-1]。
The imaging performance of metal plate/phosphor screens which are used for the creation of portal images in radiotherapy is investigated by using Monte Carlo simulations. To this end the modulation transfer function, the noise power spectrum and the detective quantum efficiency [DQE(f)] are calculated for different metals and phosphors and different thicknesses of metal and phosphor for a range of spatial resolutions. The interaction of x-rays with the metal plate/phosphor screen is modeled with the EGS4 electron gamma shower code. Optical transport in the phosphor is modeled by simulating scattering and reabsorption events of individual optical photons. It is shown that metals with a high atomic number perform better than lighter metals in maximizing the DQE(f). It is furthermore shown that the DQE(f) for the metal plate/phosphor screen alone is nearly x-ray quantum absorption limited up to spatial frequencies of 0.4 cycles/mm. In addition, it is argued that the secondary quantum sink of optical photons imposed by the optical chain (mirror, lenses and video camera) leads to a significant degradation of the signal-to-noise ratio at spatial frequencies which are most important for successful registration of portal images. Therefore, the conclusion is that a replacement of the optical chain by a flat array of photodiodes placed directly under the phosphor will lead to a substantial improvement in image quality of portal images. (C) 1999 American Association of Physicists in Medicine. [S0094-2405(99)01710-1].