Monte Carlo modelling of a-Si EPID response: the effect of spectral variations with field size and position.
Monte Carlo modelling of a-Si EPID response: the effect of spectral variations with field size and position.
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a-Si EPID 响应的蒙特卡罗建模：光谱变化随场大小和位置的影响。
DOI：
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发表时间：
2006
期刊：
影响因子：
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通讯作者：
D. Dance
中科院分区：
文献类型：
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作者：
L. Parent;J. Seco;P. Evans;A. Fielding;D. Dance
本研究的重点是使用蒙特卡罗方法预测光束中没有衰减材料的情况下调强放射治疗 (IMRT) 场的电子射野成像设备 (EPID) 图像。由于 IMRT 治疗由一系列不同尺寸的分段组成，这些分段并不总是在中心轴上进行，因此分段之间可能会观察到较大的光谱变化。通过不同尺寸和离轴位置的场研究了这些光谱变化对 EPID 响应的影响。 EPID 的详细描述是在蒙特卡罗模型中实现的。通过比较等中心点处 1 x 1 和 26 x 26 cm2 之间射野尺寸的 EPID 输出因子来验证 EPID 模型。蒙特卡洛模拟与测量结果的吻合度在 1.5% 以内。蒙特卡罗模型成功预测了不同大小的场中心的 EPID 响应，并且偏移量在测量值的 1% 以内。在不同偏移之间观察到 EPID 响应存在较大变化（高达 29%）。在大多数情况下，EPID 响应随着场大小和场偏移的增加而增加。然后使用蒙特卡罗模型来预测在射束轴上传递并带有偏移的简单测试 IMRT 场的图像。我们发现在轴交付和离轴交付之间 EPID 响应的变化高达 28%。最后，模拟两个临床 IMRT 场并与测量结果进行比较。对于所有 IMRT 视野，98% 的像素的模拟和测量结果一致在 3%-0.2 cm 范围内。通过从场中心的光谱中提取总光子产量 (Ytotal)、低于 1 MeV 的光子产量 (Ylow) 以及低于 1 MeV 的光子百分比 (Plow) 来量化光谱变化。对于研究案例，EPID 响应变化与 Ytotal、Ylow 和 Plow 之间显示出相关性。
This study focused on predicting the electronic portal imaging device (EPID) image of intensity modulated radiation treatment (IMRT) fields in the absence of attenuation material in the beam with Monte Carlo methods. As IMRT treatments consist of a series of segments of various sizes that are not always delivered on the central axis, large spectral variations may be observed between the segments. The effect of these spectral variations on the EPID response was studied with fields of various sizes and off-axis positions. A detailed description of the EPID was implemented in a Monte Carlo model. The EPID model was validated by comparing the EPID output factors for field sizes between 1 x 1 and 26 x 26 cm2 at the isocenter. The Monte Carlo simulations agreed with the measurements to within 1.5%. The Monte Carlo model succeeded in predicting the EPID response at the center of the fields of various sizes and offsets to within 1% of the measurements. Large variations (up to 29%) of the EPID response were observed between the various offsets. The EPID response increased with field size and with field offset for most cases. The Monte Carlo model was then used to predict the image of a simple test IMRT field delivered on the beam axis and with an offset. A variation of EPID response up to 28% was found between the on- and off-axis delivery. Finally, two clinical IMRT fields were simulated and compared to the measurements. For all IMRT fields, simulations and measurements agreed within 3%-0.2 cm for 98% of the pixels. The spectral variations were quantified by extracting from the spectra at the center of the fields the total photon yield (Ytotal), the photon yield below 1 MeV (Ylow), and the percentage of photons below 1 MeV (Plow). For the studied cases, a correlation was shown between the EPID response variation and Ytotal, Ylow, and Plow.
影响因子：
3.8
作者：
ROGERS, DWO;FADDEGON, BA;MACKIE, TR
通讯作者：
MACKIE, TR