Haverkamp Uwe, Norkus Darius, Kriz Jan, Müller Minai Mariam, Prott Franz-Josef, Eich Hans Theodor
Department of Radiotherapy, University Muenster, Albert-Schweitzer-Campus 1, 48129, Münster, Germany,
Strahlenther Onkol. 2014 Oct;190(11):1053-9. doi: 10.1007/s00066-014-0688-z. Epub 2014 Jun 28.
Physical 3D treatment planning provides a pool of parameters describing dose distributions. It is often useful to define conformal indices to enable quicker evaluation. However, the application of individual indices is controversial and not always effective. The aim of this study was to design a quick check of dose distributions based on several indices detecting underdosages within planning target volumes (PTVs) and overdosages in normal tissue.
Dose distributions of 215 cancer patients were considered. Treatment modalities used were three-dimensional conformal radiotherapy (3DCRT), radiosurgery, intensity-modulated radiotherapy (IMRT), intensity-modulated arc therapy (IMAT) and tomotherapy. The volumes recommended in ICRU 50 and 83 were used for planning and six conformation and homogeneity indices were selected: CI, CN, CICRU, COV, C∆, and HI. These were based on the PTV, the partial volume covered by the prescribed isodose (PI; PTVPI), the treated volume (TVPI), near maximum D2 and near minimum D98. Results were presented as a hexagon-the corners of which represent the values of the indices-and a modified test function F (Rosenbrock's function) was calculated. Results refer to clinical examples and mean values, in order to allow evaluation of the power of F and hexagon-based decision support procedures in detail and in general.
IMAT and tomotherapy showed the best values for the indices and the lowest standard deviation followed by static IMRT. DCRT and radiosurgery (e.g. CN: IMAT 0.85 ± 0.06; tomotherapy 0.84 ± 0.06; IMRT 0.83 ± 0.07; 3DCRT 0.65 ± 0.08; radiosurgery 0.64 ± 0.11). In extreme situations, not all indices reflected the situation correctly. Over- and underdosing of PTV and normal tissue could be qualitatively assessed from the distortion of the hexagon in graphic analysis. Tomotherapy, IMRT, IMAT, 3DCRT and radiosurgery showed increasingly distorted hexagons, the type of distortion indicating exposure of normal tissue volumes. The calculated F values correlated with these observations.
An evaluation of dose distributions cannot be based on a single conformal index. A solution could be the use of several indices presented as a hexagonal graphic and/or as a test function.
物理三维治疗计划提供了一系列描述剂量分布的参数。定义适形指数以便进行更快的评估通常很有用。然而，单个指数的应用存在争议且并非总是有效。本研究的目的是基于几个指数设计一种对剂量分布的快速检查方法，这些指数用于检测计划靶区（PTV）内的剂量不足以及正常组织中的剂量过量。
考虑了215例癌症患者的剂量分布。所使用的治疗方式包括三维适形放疗（3DCRT）、放射外科、调强放疗（IMRT）、调强弧形放疗（IMAT）和断层放疗。采用国际辐射单位与测量委员会（ICRU）50和83中推荐的体积进行计划，并选择了六个适形和均匀性指数：CI、CN、CICRU、COV、C∆和HI。这些指数基于PTV、处方等剂量线覆盖的部分体积（PI；PTVPI）、治疗体积（TVPI）、接近最大剂量D2和接近最小剂量D98。结果以六边形表示（其角点代表指数值），并计算了一个修改后的测试函数F（罗森布罗克函数）。结果涉及临床实例和平均值，以便详细且全面地评估F和基于六边形的决策支持程序的效能。
IMAT和断层放疗的指数值最佳且标准差最低，其次是静态IMRT。DCRT和放射外科（例如CN：IMAT为0.85±0.06；断层放疗为0.84±0.06；IMRT为0.83±0.07；3DCRT为0.65±0.08；放射外科为0.64±0.11）。在极端情况下，并非所有指数都能正确反映情况。通过图形分析中六边形的变形可以定性评估PTV和正常组织的剂量过量和不足情况。断层放疗、IMRT、IMAT、3DCRT和放射外科的六边形变形程度逐渐增加，变形类型表明正常组织体积的暴露情况。计算得到的F值与这些观察结果相关。
剂量分布的评估不能基于单个适形指数。一种解决方案可以是使用几个以六边形图形和/或测试函数形式呈现的指数。
