Olsson C, Thor M, Liu M, Moissenko V, Petersen S E, Høyer M, Apte A, Deasy J O
Division of Clinical Cancer Epidemiology, Department of Oncology, Institute of Clinical Sciences, the Sahlgrenska Academy at the University of Gothenburg, Sweden.
Phys Med Biol. 2014 Jul 21;59(14):3749-59. doi: 10.1088/0031-9155/59/14/3749. Epub 2014 Jun 17.
When pooling retrospective data from different cohorts, slice thicknesses of acquired computed tomography (CT) images used for treatment planning may vary between cohorts. It is, however, not known if varying slice thickness influences derived dose-response relationships. We investigated this for rectal bleeding using dose-volume histograms (DVHs) of the rectum and rectal wall for dose distributions superimposed on images with varying CT slice thicknesses. We used dose and endpoint data from two prostate cancer cohorts treated with three-dimensional conformal radiotherapy to either 74 Gy (N = 159) or 78 Gy (N = 159) at 2 Gy per fraction. The rectum was defined as the whole organ with content, and the morbidity cut-off was Grade ≥2 late rectal bleeding. Rectal walls were defined as 3 mm inner margins added to the rectum. DVHs for simulated slice thicknesses from 3 to 13 mm were compared to DVHs for the originally acquired slice thicknesses at 3 and 5 mm. Volumes, mean, and maximum doses were assessed from the DVHs, and generalized equivalent uniform dose (gEUD) values were calculated. For each organ and each of the simulated slice thicknesses, we performed predictive modeling of late rectal bleeding using the Lyman-Kutcher-Burman (LKB) model. For the most coarse slice thickness, rectal volumes increased (≤18%), whereas maximum and mean doses decreased (≤0.8 and ≤4.2 Gy, respectively). For all a values, the gEUD for the simulated DVHs were ≤1.9 Gy different than the gEUD for the original DVHs. The best-fitting LKB model parameter values with 95% CIs were consistent between all DVHs. In conclusion, we found that the investigated slice thickness variations had minimal impact on rectal dose-response estimations. From the perspective of predictive modeling, our results suggest that variations within 10 mm in slice thickness between cohorts are unlikely to be a limiting factor when pooling multi-institutional rectal dose data that include slice thickness variations within this range.
在汇总来自不同队列的回顾性数据时，用于治疗计划的获取的计算机断层扫描（CT）图像的切片厚度在不同队列之间可能会有所不同。然而，尚不清楚不同的切片厚度是否会影响推导的剂量反应关系。我们使用直肠和直肠壁的剂量体积直方图（DVH）来研究这一问题，这些剂量分布叠加在具有不同CT切片厚度的图像上，研究对象为直肠出血。我们使用了两个前列腺癌队列的剂量和终点数据，这两个队列接受三维适形放疗，每次分割剂量为2Gy，总剂量分别为74Gy（N = 159）或78Gy（N = 159）。直肠被定义为包含内容物的整个器官，发病率截止值为直肠晚期出血≥2级。直肠壁被定义为在直肠上增加3mm的内边缘。将模拟切片厚度从3mm到13mm的DVH与原始获取的3mm和5mm切片厚度的DVH进行比较。从DVH中评估体积、平均剂量和最大剂量，并计算广义等效均匀剂量（gEUD）值。对于每个器官和每个模拟切片厚度，我们使用Lyman-Kutcher-Burman（LKB）模型对直肠晚期出血进行预测建模。对于最粗的切片厚度，直肠体积增加（≤18%），而最大剂量和平均剂量降低（分别≤0.8Gy和≤4.2Gy）。对于所有a值，模拟DVH的gEUD与原始DVH的gEUD相差≤1.9Gy。所有DVH之间，拟合最佳的LKB模型参数值及其95%置信区间是一致的。总之，我们发现所研究的切片厚度变化对直肠剂量反应估计的影响最小。从预测建模角度来看，我们的结果表明，当汇总多机构直肠剂量数据（包括该范围内的切片厚度变化）时，队列之间切片厚度在10mm内的变化不太可能成为限制因素。
