Measurement of cone beam CT coincidence with megavoltage isocentre and image sharpness using the QUASAR™ Penta-Guide phantom
Measurement of cone beam CT coincidence with megavoltage isocentre and image sharpness using the QUASAR™ Penta-Guide phantom
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DOI：
10.1088/0031-9155/53/19/002
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发表时间：
2008-10-07
影响因子：
3.5
通讯作者：
Thwaites, D. I.
中科院分区：
文献类型：
--
作者：
Sykes, J. R.;Lindsay, R.;Thwaites, D. I.
对于基于集成在直线加速器中的锥束CT(CBCT)的图像引导放射治疗(IGRT)系统，成像器与X射线源的可重复对准对于X射线体积图像与兆伏(MV)束等中心的配准和图像的清晰度都是至关重要的。开发了一种利用QUASAR(TM)五元导体模确定CBCT到MV等中心对准的改进方法，提高了精密度和准确度。这是以我们现有的方法为基准的，该方法使用了软件和Elekta提供的滚珠轴承(BB)模型。此外，还提出了一种由五角形模体内球形气腔的边缘响应函数来测量图像清晰度(MTF50)的方法，并通过模拟千伏成像器的失调来测试其灵敏度。重复性测试表明，与BB法相比，改进的五元导引法的系统误差为0.2 mm，具有几乎相等的随机误差(S=0.15 mm)。五次测量的平均MTF50为0.278+/-0.004 1p mm(-1)，没有应用错位。模拟的失调在MTF50中显示了一个清晰的峰值，使得能够检测到大于0.4 mm的失调。五导体模可用于精确测量CBCT-IGRT系统的CBCT-MV符合度和图像清晰度。
For image-guided radiotherapy (IGRT) systems based on cone beam CT (CBCT) integrated into a linear accelerator, the reproducible alignment of imager to x-ray source is critical to the registration of both the x-ray-volumetric image with the megavoltage (MV) beam isocentre and image sharpness. An enhanced method of determining the CBCT to MV isocentre alignment using the QUASAR (TM) Penta-Guide phantom was developed which improved both precision and accuracy. This was benchmarked against our existing method which used software and a ball-bearing (BB) phantom provided by Elekta. Additionally, a method of measuring an image sharpness metric (MTF50) from the edge response function of a spherical air cavity within the Penta-Guide phantom was developed and its sensitivity was tested by simulating misalignments of the kV imager. Reproducibility testing of the enhanced Penta-Guide method demonstrated a systematic error of < 0.2 mm when compared to the BB method with near equivalent random error (s = 0.15 mm). The mean MTF50 for five measurements was 0.278 +/- 0.004 1p mm(-1) with no applied misalignment. Simulated misalignments exhibited a clear peak in the MTF50 enabling misalignments greater than 0.4 mm to be detected. The Penta-Guide phantom can be used to precisely measure CBCT-MV coincidence and image sharpness on CBCT-IGRT systems.