Kirisits Christian, Siebert Frank-André, Baltas Dimos, De Brabandere Marisol, Hellebust Taran Paulsen, Berger Daniel, Venselaar Jack
Department of Radiotherapy, Medical University of Vienna, Vienna, Austria.
Radiother Oncol. 2007 Sep;84(3):290-7. doi: 10.1016/j.radonc.2007.06.010. Epub 2007 Aug 14.
To determine the uncertainties in dose volume histogram (DVH) analysis used in modern brachytherapy treatment planning systems (TPSs).
A phantom with three different volumes was scanned with CT and MRI. An inter-observer analysis was based on contouring performed by 5 persons. The volume of a standard contour set was calculated using seven different TPSs. For five systems a typical brachytherapy dose distribution was used to compare DVH determination.
The inter-observer variability (1SD) was 13% for a small cylindrical volume, 5% for a large cylinder and 3% for a conical shape. A standardized volume for a 4mm CT scan contoured on seven different TPS varied by 7%, 2%, and 5% (1SD). Use of smaller slice thickness reduced the variations. A treatment plan with the sources between the large cylindrical shape and the cone showed variations for D(2cc) of 1% and 5% (1SD), respectively. Deviations larger than 10% were observed for a smaller source to cylinder surface distance of 5mm.
Modern TPSs minimize the volumetric and dosimetric calculation uncertainties. These are comparable to inter-observer contouring variations. However, differences in volume result from the methods of calculation in the first and last slice of a contoured structure. For this situation and in case of high dose gradients inside analyzed volumes, high uncertainties were observed. The use of DVH parameters in clinical practice should take into account the method of calculation and the possible uncertainties.
确定现代近距离放射治疗治疗计划系统（TPS）中剂量体积直方图（DVH）分析的不确定性。
使用CT和MRI扫描具有三种不同体积的体模。观察者间分析基于5人进行的轮廓勾画。使用七种不同的TPS计算标准轮廓集的体积。对于五个系统，使用典型的近距离放射治疗剂量分布来比较DVH的确定。
对于小圆柱形体积，观察者间变异性（1标准差）为13%，大圆柱体为5%，圆锥体为3%。在七种不同的TPS上对4mm CT扫描进行轮廓勾画得到的标准化体积变化分别为7%、2%和5%（1标准差）。使用更薄的切片厚度可减少变化。源位于大圆柱体和圆锥体之间的治疗计划中，D(2cc)的变化分别为1%和5%（1标准差）。对于源到圆柱体表面距离为5mm的较小情况，观察到偏差大于10%。
现代TPS将体积和剂量计算的不确定性降至最低。这些不确定性与观察者间轮廓勾画的变化相当。然而，体积差异源于轮廓结构的第一和最后一层切片的计算方法。对于这种情况以及分析体积内存在高剂量梯度的情况，观察到高不确定性。在临床实践中使用DVH参数时应考虑计算方法和可能的不确定性。
