Stroom J C, Korevaar G A, Koper P C, Visser A G, Heijmen B J
Department of Clinical Physics, University Hospital Rotterdam, Daniel den Hoed Cancer Center, The Netherlands.
Radiother Oncol. 1998 Jun;47(3):297-302. doi: 10.1016/s0167-8140(98)00026-7.
To demonstrate the need for a fully three-dimensional (3D) computerized expansion of the gross tumour volume (GTV) or clinical target volume (CTV), as delineated by the radiation oncologist on CT slices, to obtain the proper planning target volume (PTV) for treatment planning according to the ICRU-50 recommendations.
For 10 prostate cancer patients two PTVs have been determined by expansion of the GTV with a 1.5 cm margin, i.e. a 3D PTV and a multiple 2D PTV. The former was obtained by automatically adding the margin while accounting in 3D for GTV contour differences in neighbouring slices. The latter was generated by automatically adding the 1.5 cm margin to the GTV in each CT slice separately; the resulting PTV is a computer simulation of the PTV that a radiation oncologist would obtain with (the still common) manual contouring in CT slices. For each patient the two PTVs were compared to assess the deviations of the multiple 2D PTV from the 3D PTV. For both PTVs conformal plans were designed using a three-field technique with fixed block margins. For each patient dose-volume histograms and tumour control probabilities (TCPs) of the (correct) 3D PTV were calculated, both for the plan designed for this PTV and for the treatment plan based on the (deviating) 2D PTV.
Depending on the shape of the GTV, multiple 2D PTV generation could locally result in a 1 cm underestimation of the GTV-to-PTV margin. The deviations occurred predominantly in the cranio-caudal direction at locations where the GTV contour shape varies significantly from slice to slice. This could lead to serious underdosage and to a TCP decrease of up to 15%.
A full 3D GTV-to-PTV expansion should be applied in conformal radiotherapy to avoid underdosage.
根据国际辐射单位与测量委员会（ICRU）-50号建议，证明有必要对放射肿瘤学家在CT切片上勾画的大体肿瘤体积（GTV）或临床靶体积（CTV）进行全三维（3D）计算机扩展，以获得用于治疗计划的合适计划靶体积（PTV）。
对于10例前列腺癌患者，通过在GTV上添加1.5 cm的边界来确定两个PTV，即一个3D PTV和一个多个二维PTV。前者是通过在三维空间中考虑相邻切片中GTV轮廓差异的同时自动添加边界而获得的。后者是通过在每个CT切片中分别自动向GTV添加1.5 cm的边界而生成的；所得的PTV是放射肿瘤学家在CT切片中通过（仍然常见的）手动勾画获得的PTV的计算机模拟。对于每位患者，比较两个PTV以评估多个二维PTV与三维PTV的偏差。对于两个PTV，均使用具有固定挡块边界的三野技术设计适形计划。对于每位患者，计算了针对该PTV设计的计划以及基于（有偏差的）二维PTV的治疗计划的（正确的）三维PTV的剂量体积直方图和肿瘤控制概率（TCP）。
根据GTV的形状，多个二维PTV的生成可能会在局部导致GTV到PTV边界的低估达1 cm。偏差主要发生在头足方向上GTV轮廓形状在各切片之间有显著变化的位置。这可能导致严重的剂量不足，并导致TCP降低高达15%。
在适形放射治疗中应应用全三维GTV到PTV的扩展，以避免剂量不足。
