Department of Radiation Oncology, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands.
Department of Radiation Oncology, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands.
Int J Radiat Oncol Biol Phys. 2014 Jul 1;89(3):641-8. doi: 10.1016/j.ijrobp.2014.03.029. Epub 2014 May 3.
Because of low soft-tissue contrast of cone beam computed tomography (CBCT), fiducial markers are often used for radiation therapy patient setup verification. For pancreatic cancer patients, biliary stents have been suggested as surrogate fiducials. Using intratumoral fiducials as standard for tumor position, this study aims to quantify the suitability of biliary stents for measuring interfractional and respiratory-induced position variations of pancreatic tumors.
Eleven pancreatic cancer patients with intratumoral fiducials and a biliary stent were included in this study. Daily CBCT scans (243 in total) were registered with a reference CT scan, based on bony anatomy, on fiducial markers, and on the biliary stent, respectively. We analyzed the differences in tumor position (ie, markers center-of-mass position) among these 3 registrations. In addition, we measured for 9 patients the magnitude of respiratory-induced motion (MM) of the markers and of the stent on 4-dimensional CT (4DCT) and determined the difference between these 2 magnitudes (ΔMM).
The stent indicated tumor position better than bony anatomy in 67% of fractions; the absolute difference between the markers and stent registration was >5 mm in 46% of fractions and >10 mm in 20% of fractions. Large PTV margins (superior-inferior direction, >19 mm) would be needed to account for this interfractional position variability. On 4DCT, we found in superior-inferior direction a mean ΔMM of 0.5 mm (range, -2.6 to 4.2 mm).
For respiratory-induced motion, the mean ΔMM is small, but for individual patients the absolute difference can be >4 mm. For interfractional position variations, a stent is, on average, a better surrogate fiducial than bony anatomy, but large PTV margins would still be required. Therefore, intratumoral fiducials are recommended for online setup verification for all pancreatic patients scheduled for radiation therapy, including patients with a biliary stent.
由于锥形束计算机断层扫描（CBCT）软组织对比度低，因此通常使用基准标记物来验证放射治疗患者的设置。对于胰腺癌患者，已经提出胆管支架作为替代基准标记物。本研究使用肿瘤内基准标记物作为肿瘤位置的标准，旨在定量测量胆管支架测量胰腺肿瘤分次间和呼吸诱导的位置变化的适用性。
本研究纳入了 11 名具有肿瘤内基准标记物和胆管支架的胰腺癌患者。每天进行 CBCT 扫描（总共 243 次），并根据骨解剖结构、基准标记物和胆管支架分别与参考 CT 扫描进行配准。我们分析了这 3 种配准方法中肿瘤位置（即标记物质心位置）的差异。此外，我们还对 9 名患者进行了测量，以确定标记物和支架在 4 维 CT（4DCT）上的呼吸诱导运动幅度（MM），并确定这两个幅度之间的差异（ΔMM）。
在 67%的分次中，支架指示的肿瘤位置优于骨解剖结构；在 46%的分次中，标记物和支架配准的绝对差异大于 5mm，在 20%的分次中，绝对差异大于 10mm。为了弥补这种分次间位置变化，需要较大的 PTV 边界（上下方向，>19mm）。在 4DCT 上，我们发现上下方向的平均 ΔMM 为 0.5mm（范围，-2.6 至 4.2mm）。
对于呼吸诱导的运动，平均 ΔMM 较小，但对于个别患者，绝对差异可能大于 4mm。对于分次间位置变化，支架平均是比骨解剖结构更好的替代基准标记物，但仍需要较大的 PTV 边界。因此，对于所有接受放射治疗的胰腺癌患者，包括有胆管支架的患者，建议使用肿瘤内基准标记物进行在线设置验证。
