Division of Cancer Sciences, School of Medical Sciences, Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, UK.
Department of Radiation Oncology, Amsterdam University Medical Center, University of Amsterdam, Amsterdam, the Netherlands.
Clin Oncol (R Coll Radiol). 2020 Dec;32(12):835-844. doi: 10.1016/j.clon.2020.09.011. Epub 2020 Oct 13.
In image-guided radiotherapy, daily cone-beam computed tomography (CBCT) is rarely applied to children due to concerns over imaging dose. Simulating low-dose CBCT can aid clinical protocol design by allowing visualisation of new scan protocols in patients without delivering additional dose. This work simulated ultra-low-dose CBCT and evaluated its use for paediatric image-guided radiotherapy by assessment of image registration accuracy and visual image quality.
Ultra-low-dose CBCT was simulated by adding the appropriate amount of noise to projection images prior to reconstruction. This simulation was validated in phantoms before application to paediatric patient data. Scans from 20 patients acquired at our current clinical protocol (0.8 mGy) were simulated for a range of ultra-low doses (0.5, 0.4, 0.2 and 0.125 mGy) creating 100 scans in total. Automatic registration accuracy was assessed in all 100 scans. Inter-observer registration variation was next assessed for a subset of 40 scans (five scans at each simulated dose and 20 scans at the current clinical protocol). This subset was assessed for visual image quality by Likert scale grading of registration performance and visibility of target coverage, organs at risk, soft-tissue structures and bony anatomy.
Simulated and acquired phantom scans were in excellent agreement. For patient scans, bony atomy registration discrepancies for ultra-low-dose scans fell within 2 mm (translation) and 1° (rotation) compared with the current clinical protocol, with excellent inter-observer agreement. Soft-tissue registration showed large discrepancies. Bone visualisation and registration performance reached over 75% acceptability (rated 'well' or 'very well') down to the lowest doses. Soft-tissue visualisation did not reach this threshold for any dose.
Ultra-low-dose CBCT was accurately simulated and evaluated in patient data. Patient scans simulated down to 0.125 mGy were appropriate for bony anatomy set-up. The large dose reduction could allow for more frequent (e.g. daily) image guidance and, hence, more accurate set-up for paediatric radiotherapy.
在图像引导放疗中，由于对成像剂量的担忧，很少对儿童进行锥形束计算机断层扫描（CBCT）。通过模拟低剂量 CBCT，可以在不给患者额外剂量的情况下，在新的扫描方案中可视化患者，从而帮助临床方案设计。本工作通过评估图像配准精度和视觉图像质量，模拟超低剂量 CBCT 并评估其在儿科图像引导放疗中的应用。
通过在重建前向投影图像添加适量噪声来模拟超低剂量 CBCT。在将其应用于儿科患者数据之前，在体模中验证了这种模拟。对我们当前临床方案（0.8 mGy）采集的 20 名患者的扫描进行了一系列超低剂量（0.5、0.4、0.2 和 0.125 mGy）模拟，总共生成 100 个扫描。在所有 100 个扫描中评估自动配准精度。接下来，对于 40 个扫描的子集（每个模拟剂量五个扫描，当前临床方案 20 个扫描）评估观察者间配准变化。通过对注册性能和靶区覆盖、危及器官、软组织结构和骨解剖结构的可视性进行李克特量表评分，评估该子集的视觉图像质量。
模拟和采集的体模扫描非常吻合。对于患者扫描，与当前临床方案相比，超低剂量扫描的骨性解剖配准差异在 2 毫米（平移）和 1 度（旋转）以内，观察者间具有很好的一致性。软组织配准显示出较大的差异。骨的可视化和配准性能在最低剂量下达到 75%以上（评为“好”或“非常好”）。对于任何剂量，软组织的可视化都没有达到这个阈值。
在患者数据中准确地模拟和评估了超低剂量 CBCT。模拟剂量低至 0.125 mGy 的患者扫描适用于骨性解剖设置。如此大的剂量减少可以允许更频繁的（例如每日）图像引导，从而为儿科放疗提供更精确的设置。
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