IEO, European Institute of Oncology IRCCS, Unit of Medical Physics, Milan, Italy.
University of Milan, Milan, Italy.
Phys Med. 2019 Jan;57:200-206. doi: 10.1016/j.ejmp.2019.01.009. Epub 2019 Jan 15.
The aim of this study is to evaluate the dose delivered and the image quality of pre-treatment MVCT images with Hi-Art TomoTherapy system, varying acquisition and reconstruction parameters.
Catphan 500 MVCT images were acquired with all acquisition pitch and reconstruction intervals; image quality was evaluated in terms of noise, uniformity, contrast linearity, contrast-to-noise ratio (CNR) and spatial resolution with the Modulation Transfer Function (MTF). Dose was evaluated as Multi Slice Average Dose (MSAD) and measurements were performed with the Standard TomoTherapy® Quality Assurance Kit composed by the TomoTherapy Phantom, the Exradin A1SL ion chamber and TomoElectrometer. For each pitch-reconstruction interval, acquisitions were repeated 5 times.
Differences in noise and uniformity, though statistically significant in some cases, were very small: noise ranged from 2.3% for Coarse - 3 mm to 2.4% for Coarse - 6 mm, while uniformity passed from 99.5% for Coarse - 6 mm to 99.8% for Normal - 4 mm. No differences at all were found for CNR for high and low density inserts, while MTF was higher for pitch Coarse, even if no differences in spatial resolution were observed visually (spatial resolution was up to 4 lp/cm for all combinations of pitch and reconstruction interval). Dose was dependent on pitch, being 1.0 cGy for Coarse, 1.5 cGy for Normal and 2.85 cGy for Fine.
We observed negligible differences in image quality among different pitch and reconstruction interval, thus, considerations regarding pre-treatment imaging modalities should be based only on dose delivered and on the desired resolution along the cranio-caudal axis for image-guided radiotherapy and adaptive radiotherapy purposes.
本研究旨在评估在不同采集和重建参数下，Hi-Art TomoTherapy 系统的治疗前 MVCT 图像的剂量分布和图像质量。
采用全采集螺距和重建间隔，对 Catphan 500 MVCT 图像进行采集；使用调制传递函数（MTF），从噪声、均匀性、对比度线性、对比噪声比（CNR）和空间分辨率等方面评估图像质量；采用标准的 TomoTherapy 质量保证套件（由 TomoTherapy 体模、Exradin A1SL 电离室和 TomoElectrometer 组成）对剂量进行评估，采用多切片平均剂量（MSAD）进行测量。对于每个螺距-重建间隔，采集重复 5 次。
尽管在某些情况下差异具有统计学意义，但噪声和均匀性的差异非常小：噪声范围从粗-3mm 的 2.3%到粗-6mm 的 2.4%，而均匀性从粗-6mm 的 99.5%到正常-4mm 的 99.8%。对于高低密度插件的 CNR，没有发现差异，而 MTF 对于粗螺距更高，即使在空间分辨率方面没有观察到差异（所有螺距和重建间隔的组合的空间分辨率高达 4lp/cm）。剂量取决于螺距，粗螺距为 1.0cGy，正常螺距为 1.5cGy，细螺距为 2.85cGy。
我们观察到不同螺距和重建间隔之间的图像质量差异可以忽略不计，因此，对于治疗前成像方式的考虑应该仅基于剂量分布和为图像引导放疗和自适应放疗目的所需的沿颅尾轴的分辨率。
