Mayyas E, Wen N, Liu D, Glide-Hurst C, Ajlouni M, Chetty I
Henry Ford Health System, Detroit, MI.
Med Phys. 2012 Jun;39(6Part24):3910. doi: 10.1118/1.4735959.
Steep dose gradients and high dose per fraction in stereotactic ablative radiation therapy (SABR or SBRT) necessitate highly accurate tumor localization. This study evaluates inter-fraction shifts, as defined by couch correction analysis, and investigates the effect of tumor location and internal target volume (ITV) on these shifts. In addition, residual errors associated with post-CBCT correction and their dosimetric consequences were quantified.
Daily free-breathing (FB) CBCT images used for daily localization of 78 patients with non-small cell lung cancer were retrospectively evaluated. Among the population, 39 patients also received pre-treatment kV images after CBCT alignment. ITV inter-fraction displacement was evaluated by matching the CBCT and the FB helical CT images, and setup errors were quantified using orthogonal kV images. Associations between ITV location and inter-fraction motion were studied by categorizing tumors into the following locations: chest-wall seated (CWS) and island, peripheral, central, or upper, middle and lower. Dosimetric consequences for the patient with the largest setup error were explored.
ITV inter-fraction motion included the mean of the systematic error, ?inter=(-1.4, 2.0, 1.6) mm, standard deviation (SD) of the systematic error, Σinter=(2.1, 4.2, 2.9) mm, and SD of random errors, sinter=(2.2, 3.2, 3.6) mm. No significant associations were observed between inter-fraction shifts and tumor location or volume. Using CBCT for image guidance reduced the observed errors to μsetup=(-0.3, 0.1, 0.0) mm, Σsetup=(0.6, 0.6, 0.4) mm and ssetup=(1.2, 0.7, 0.7) mm. Dosimetric consequences for the patient with the largest setup error were explored. It was shown that a 3.0 mm setup margin was sufficient to provide greater than 95% dose coverage to the ITV.
CBCT image guidance reduced setup errors significantly such that 2-3 mm, population-based, setup margins provided proper dose coverage to the ITV. Further investigation of inter-and intrafraction error classification by tumor location is warranted.
立体定向消融放疗（SABR 或 SBRT）中陡峭的剂量梯度和高的分次剂量需要高度精确的肿瘤定位。本研究评估了由治疗床校正分析定义的分次间位移，并研究了肿瘤位置和内部靶区体积（ITV）对这些位移的影响。此外，还对与CBCT校正后相关的残余误差及其剂量学后果进行了量化。
回顾性评估了用于78例非小细胞肺癌患者每日定位的每日自由呼吸（FB）CBCT图像。在这些患者中，39例患者在CBCT校准后还接受了治疗前的kV图像。通过匹配CBCT和FB螺旋CT图像评估ITV分次间位移，并使用正交kV图像对摆位误差进行量化。通过将肿瘤分类为以下位置来研究ITV位置与分次间运动之间的关联：胸壁占位（CWS）和岛状、周围型、中央型或上、中、下型。探讨了摆位误差最大的患者的剂量学后果。
ITV分次间运动包括系统误差的均值，?inter=（-1.4, 2.0, 1.6）mm，系统误差的标准差，Σinter=（2.1, 4.2, 2.9）mm，以及随机误差的标准差，sinter=（2.2, 3.2, 3.6）mm。未观察到分次间位移与肿瘤位置或体积之间存在显著关联。使用CBCT进行图像引导将观察到的误差降低至μsetup=（-0.3, 0.1, 0.0）mm，Σsetup=（0.6, 0.6, 0.4）mm和ssetup=（1.2, 0.7, 0.7）mm。探讨了摆位误差最大的患者的剂量学后果。结果表明，3.0mm的摆位边界足以向ITV提供大于95%的剂量覆盖。
CBCT图像引导显著降低了摆位误差，使得基于人群的2-3mm摆位边界能够为ITV提供合适的剂量覆盖。有必要进一步按肿瘤位置对分次间和分次内误差分类进行研究。
