Department of Physics and Astronomy, University of Victoria, Victoria, British Columbia, Canada.
Med Phys. 2022 Apr;49(4):2334-2341. doi: 10.1002/mp.15503. Epub 2022 Feb 16.
To investigate cone beam computed tomography (CBCT) image quality using novel combinations of kilovoltage (kV) and megavoltage (MV) beams and detector materials.
MV and kV CBCT imaging was simulated using the Fastcat hybrid Monte Carlo application. CBCT imaging with various beam energies was investigated: 2.5 and 6 MV photon beams generated with carbon, aluminum, and tungsten targets and a 120 kVp x-ray tube beam based off of a Varian Truebeam on-board imager (OBI). Cadmium tungstate (CWO), gadolinium oxysulfide (GOS), and cesium iodide (CsI) detectors with identical pixel pitch of 0.784 mm were evaluated. Modulation transfer functions (MTF) for all detector/beam combinations were calculated. MV and kV CBCT images for each detector/beam combination of a contrast phantom containing inserts with rib and spongiosa bone, lung, and adipose tissues were simulated with an imaging dose of 7 mGy. Contrast to noise ratio (CNR) of all inserts were compared for all detector/beam combinations. CBCT images of an anthropomorphic head phantom with silver amalgam fillings were also generated.
The CWO/120 kVp beam combination resulted in the highest MTF at low frequencies and the CsI detector showed the highest MTF for all other beams and at high frequencies. The CWO/120 kVp beam combination showed the highest CNR for all tissues. The unoptimized CWO/2.5 MV carbon target beam showed the highest CNR of the MV beam/detector combinations with CNR 4% and 17% worse than the optimized Truebeam CsI 120 kVp setup with a bowtie filter and antiscatter grid. Additionally, the CWO 2.5 MV setup showed qualitative reduction of metal artifacts surrounding silver amalgam fillings in an anthropomorphic head phantom.
This finding makes a compelling case that further optimization of this CWO carbon target setup could produce CBCT images with similar CNR to current OBI CBCT for equivalent dose with added resilience to metal artifacts.
研究使用新型千伏（kV）和兆伏（MV）射线束和探测器材料组合的锥形束 CT（CBCT）图像质量。
使用 Fastcat 混合蒙特卡罗应用程序模拟 MV 和 kV CBCT 成像。研究了各种射线能量的 CBCT 成像：2.5 和 6 MV 光子射线束由碳、铝和钨靶产生，以及基于瓦里安 Truebeam 机载成像仪（OBI）的 120 kVp X 射线管射线束。评估了具有相同像素间距 0.784 mm 的碲化镉（CWO）、氧化钆硫（GOS）和碘化铯（CsI）探测器。计算了所有探测器/射线束组合的调制传递函数（MTF）。使用 7 mGy 的成像剂量模拟了对比度体模的 MV 和 kV CBCT 图像，对比度体模包含带有肋骨和松质骨、肺和脂肪组织的插件。比较了所有探测器/射线束组合的所有插件的对比噪声比（CNR）。还生成了具有银汞合金填充物的人体头部幻影的 CBCT 图像。
CWO/120 kVp 射线束组合在低频下产生最高的 MTF，而 CsI 探测器在所有其他射线束和高频下显示最高的 MTF。CWO/120 kVp 射线束组合显示所有组织的最高 CNR。未经优化的 CWO/2.5 MV 碳靶射线束显示 MV 射线束/探测器组合中最高的 CNR，与具有蝴蝶结滤波器和防散射格栅的优化后的 Truebeam CsI 120 kVp 设置相比，CNR 差 4%和 17%。此外，CWO 2.5 MV 设置显示出在人体头部幻影中围绕银汞合金填充物的金属伪影的定性减少。
这一发现有力地表明，进一步优化这种 CWO 碳靶设置可以产生与当前 OBI CBCT 类似的 CNR 图像，在相同剂量下具有对金属伪影的更强抵抗力。
