Medical Physics, Mater Misericordiae University Hospital, Dublin, Ireland.
Medical Physics, Mater Misericordiae University Hospital, Dublin, Ireland.
Phys Med. 2020 Mar;71:3-6. doi: 10.1016/j.ejmp.2020.01.021. Epub 2020 Feb 14.
Cone beam technology is becoming more prominent in Radiology. In our hospital we have an extremity CT, an O-arm and a number of C-arms offering 3D capabilities. Each of these modalities use cone beam CT (CBCT) technology to image the area of interest in one single rotation. Traditional CTDI metrics for radiation dosimetry in CT depend on narrow beam geometry. The relevance of the CTDI as a dose indicator for cone beam scanning is contentious due to underestimation of dose lying outside the standard 100 mm chamber length and CTDI phantoms being of insufficient length. In an attempt to better quantify dose from cone beam scanning, alternative methodologies have been developed which attempt to counter the limitations of CTDI methodologies. In this comparison study we utilised the CBCT methodologies outlined in (i) IAEA Report 5, (ii) EFOMP's protocol on QC in CBCT and (iii) conventional CTDI measurement and tested them on various CBCT systems used in Radiology. These methods were chosen as they use equipment that is typically available to a diagnostic imaging physicist. We determine that the EFOMP protocol and the conventional CTDI method produce the best estimate of the radiation output for quality control purposes. Our conclusion is that the EFOMP protocol is the fastest and easiest method to measure a CBCT metric but it is not always accessible. For the systems in our hospital we will adopt the EFOMP protocol for open systems (C-arms) and perform CTDI measurements using conventional techniques on enclosed systems (O-arm and extremity CT).
锥形束技术在放射学领域越来越突出。在我们医院，我们有一台四肢 CT、一台 O 臂和多台提供 3D 功能的 C 臂。这些设备中的每一种都使用锥形束 CT（CBCT）技术在单次旋转中对感兴趣的区域进行成像。传统的 CT 辐射剂量学中的 CTDI 指标取决于窄束几何形状。由于 CTDI 低估了标准 100mm 腔长度之外的剂量和 CTDI 体模长度不足，因此作为锥形束扫描剂量指标的 CTDI 的相关性存在争议。为了更好地量化锥形束扫描的剂量，已经开发了替代方法来克服 CTDI 方法的局限性。在这项比较研究中，我们使用了（i）IAEA 报告 5、（ii）EFOMP 在 CBCT 中的 QC 协议和（iii）传统的 CTDI 测量中概述的 CBCT 方法，并在放射科使用的各种 CBCT 系统上对其进行了测试。选择这些方法是因为它们使用的设备通常可供诊断成像物理学家使用。我们确定 EFOMP 协议和传统的 CTDI 方法最适合用于质量控制目的的辐射输出估计。我们的结论是，EFOMP 协议是测量 CBCT 指标最快、最简单的方法，但并非总是可行。对于我们医院的系统，我们将为开放式系统（C 臂）采用 EFOMP 协议，并使用传统技术对封闭式系统（O 臂和四肢 CT）进行 CTDI 测量。
