Department of Radiation Oncology, University Medical Center Mannheim, University of Heidelberg, Mannheim, Germany; Department of Medical Physics and Bioengineering, Christchurch Hospital, Christchurch, New Zealand.
Department of Radiation Oncology, University Medical Center Mannheim, University of Heidelberg, Mannheim, Germany.
Radiother Oncol. 2019 Jun;135:78-85. doi: 10.1016/j.radonc.2019.02.004. Epub 2019 Mar 16.
Lung tumors treated with hypo-fractionated deep-inspiration breath-hold stereotactic body radiotherapy benefit from fast imaging and treatment. Single breath-hold cone-beam-CT (CBCT) could reduce motion artifacts and improve treatment precision. Thus, gantry speed was accelerated to 18°/s, limiting acquisition time to 10-20 s. Image quality, dosimetry and registration accuracy were compared with standard-CBCT (3°/s).
For proof-of-concept, image quality was analyzed following customer acceptance tests, CT-dose index measured, and registration accuracy determined with an off-centered ball-bearing-phantom. A lung-tumor patient was simulated with differently shaped tumor-mimicking inlays in a thorax-phantom. Signal-to-noise-ratio, contrast-to-noise-ratio and geometry of the inlays quantified image quality. Dose was measured in representative positions. Registration accuracy was determined with inlays scanned in pre-defined positions. Manual, automatic (clinical software) and objective-automatic (in-house-developed) registration was performed on planning-CT, offsets between results and applied shifts were compared.
Image quality of ultrafast-CBCT was adequate for high-contrast areas, despite contrast-reduction of ∼80% due to undersampling. Dose-output was considerably reduced by 60-83% in presented setup; variations are due to gantry-braking characteristics. Registration accuracy was maintained better than 1 mm, mean displacement errors were 0.0 ± 0.2 mm with objective-automatic registration. Ultrafast-CBCT showed no significant registration differences to standard-CBCT.
This study of first tests with faster gantry rotation of 18°/s showed promising results for ultrafast high-contrast lung tumor CBCT imaging within single breath-hold of 10-20 s. Such fast imaging times, in combination with fast treatment delivery, could pave the way for intra-fractional combined imaging and treatment within one breath-hold phase, and thus mitigate residual motion and increase treatment accuracy and patient comfort. Even generally speaking, faster gantry rotation could set a benchmark with immense clinical impact where time matters most: palliative patient care, general reduction in uncertainty, and increase in patient throughput especially important for emerging markets with high patient numbers.
接受深吸气屏气立体定向体部放射治疗的肺部肿瘤得益于快速成像和治疗。单次屏气锥形束 CT（CBCT）可以减少运动伪影并提高治疗精度。因此，将机架旋转速度提高到 18°/s，将采集时间限制在 10-20s。与标准 CBCT（3°/s）相比，对图像质量、剂量学和配准精度进行了比较。
为了验证概念，根据客户验收测试分析了图像质量，测量了 CT 剂量指数，并使用偏心球轴承体模确定了配准精度。在体模中模拟了一个带有不同形状肿瘤模拟插件的肺部肿瘤患者。通过定量插件的信噪比、对比噪声比和几何形状来评估图像质量。在代表性位置测量剂量。在预定义位置扫描插件以确定配准精度。在计划 CT 上分别进行手动、自动（临床软件）和客观自动（内部开发）配准，比较结果与应用的偏移量。
尽管由于欠采样导致对比度降低了约 80%，但超快 CBCT 的图像质量对于高对比度区域仍然足够。在提出的设置中，剂量输出降低了 60-83%；变化是由于机架制动特性引起的。配准精度保持在 1mm 以内，客观自动配准的平均位移误差为 0.0±0.2mm。超快 CBCT 与标准 CBCT 相比没有明显的配准差异。
这项关于更快的 18°/s 机架旋转的首次测试研究表明，在 10-20s 的单次屏气呼吸中，超快高对比度肺部肿瘤 CBCT 成像具有良好的前景。这种快速成像时间，结合快速治疗，可为单次呼吸阶段内的分次内联合成像和治疗铺平道路，从而减轻残余运动，提高治疗精度和患者舒适度。即使一般来说，更快的机架旋转可以设定一个具有巨大临床影响的基准，在时间最重要的情况下：姑息性患者护理、普遍减少不确定性、增加患者吞吐量，这对于高患者数量的新兴市场尤其重要。
