Department of Radiation Oncology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
Int J Radiat Oncol Biol Phys. 2013 Sep 1;87(1):202-8. doi: 10.1016/j.ijrobp.2013.05.001. Epub 2013 Jun 19.
The aim of this study was to quantify interfractional pancreatic position variation using fiducial markers visible on daily cone beam computed tomography (CBCT) scans. In addition, we analyzed possible migration of the markers to investigate their suitability for tumor localization.
For 13 pancreatic cancer patients with implanted Visicoil markers, CBCT scans were obtained before 17 to 25 fractions (300 CBCTs in total). Image registration with the reference CT was used to determine the displacement of the 2 to 3 markers relative to bony anatomy and to each other. We analyzed the distance between marker pairs as a function of time to identify marker registration error (SD of linear fit residuals) and possible marker migration. For each patient, we determined the mean displacement of markers relative to the reference CT (systematic position error) and the spread in displacements (random position error). From this, we calculated the group systematic error, Σ, and group random error, σ.
Marker pair distances showed slight trends with time (range, -0.14 to 0.14 mm/day), possibly due to tissue deformation, but no shifts that would indicate marker migration. The mean SD of the fit residuals was 0.8 mm. We found large interfractional position variations, with for 116 of 300 (39%) fractions a 3-dimensional vector displacement of >10 mm. The spread in displacement varied significantly (P<.01) between patients, from a vector range of 9.1 mm to one of 24.6 mm. For the patient group, Σ was 3.8, 6.6, and 3.5 mm; and σ was 3.6, 4.7 and 2.5 mm, in left-right, superior-inferior, and anterior-posterior directions, respectively.
We found large systematic displacements of the fiducial markers relative to bony anatomy, in addition to wide distributions of displacement. These results for interfractional position variation confirm the potential benefit of using fiducial markers rather than bony anatomy for daily online position verification for pancreatic cancer patients.
本研究旨在使用在每日锥形束 CT（CBCT）扫描中可见的基准标记量化分次间胰腺位置变化。此外，我们还分析了标记物的可能迁移，以研究其对肿瘤定位的适用性。
对 13 例植入 Visicoil 标记物的胰腺癌患者，共获得 17 至 25 分次（300 次 CBCT）的 CBCT 扫描。使用与参考 CT 的图像配准来确定相对于骨解剖结构和彼此的 2 至 3 个标记物的位移。我们分析了标记物对之间的距离随时间的变化，以确定标记物配准误差（线性拟合残差的标准差）和可能的标记物迁移。对于每位患者，我们确定了标记物相对于参考 CT 的平均位移（系统位置误差）和位移的离散程度（随机位置误差）。由此，我们计算了组系统误差，Σ，和组随机误差，σ。
标记物对之间的距离随时间表现出轻微的趋势（范围为 -0.14 至 0.14 毫米/天），可能是由于组织变形所致，但没有表明标记物迁移的偏移。拟合残差的平均标准差为 0.8 毫米。我们发现分次间位置变化很大，在 300 次分次中的 116 次（39%）中，三维向量位移>10 毫米。位移的离散程度在患者之间差异显著（P<.01），从 9.1 毫米到 24.6 毫米的向量范围。对于患者组，Σ 分别为 3.8、6.6 和 3.5 毫米；σ 分别为 3.6、4.7 和 2.5 毫米，在左右、上下和前后方向。
我们发现相对于骨解剖结构，基准标记物存在较大的系统位移，同时位移分布广泛。这些分次间位置变化的结果证实了在胰腺癌患者的日常在线位置验证中使用基准标记物而不是骨解剖结构的潜在益处。
