Rietzel Eike, Liu Arthur K, Doppke Karen P, Wolfgang John A, Chen Aileen B, Chen George T Y, Choi Noah C
Department of Radiation Oncology, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA.
Int J Radiat Oncol Biol Phys. 2006 Sep 1;66(1):287-95. doi: 10.1016/j.ijrobp.2006.05.024.
When using non-patient-specific treatment planning margins, respiratory motion may lead to geometric miss of the target while unnecessarily irradiating normal tissue. Imaging different respiratory states of a patient allows patient-specific target design. We used four-dimensional computed tomography (4DCT) to characterize tumor motion and create treatment volumes in 10 patients with lung cancer. These were compared with standard treatment volumes.
Four-dimensional CT and free breathing helical CT data of 10 patients were acquired. Gross target volumes (GTV) were delineated on the helical scan as well as on each phase of the 4D data. Composite GTVs were defined on 4DCT. Planning target volumes (PTV) including clinical target volume, internal margin (IM), and setup margin were generated. 4DPTVs with different IMs and standard PTVs were compared by computing centroid positions, volumes, volumetric overlap, and bounding boxes.
Four-dimensional PTVs and conventional PTVs differed in volume and centroid positions. Overlap between 4DPTVs generated from two extreme tumor positions only compared with 10 respiratory phases was 93.7%. Comparing PTVs with margins of 15 mm (IM 5 mm) on composite 4D target volumes to PTVs with 20 mm (IM 10 mm) on helical CT data resulted in a decrease in target volume sizes by 23% on average.
With patient-specific characterization of tumor motion, it should be possible to decrease internal margins. Patient-specific treatment volumes can be generated using extreme tumor positions on 4DCT. To date, more than 150 patients have been treated using 4D target design.
在使用非患者特异性治疗计划边界时，呼吸运动可能导致靶区的几何误差，同时不必要地照射正常组织。对患者不同呼吸状态进行成像有助于进行患者特异性靶区设计。我们使用四维计算机断层扫描（4DCT）对10例肺癌患者的肿瘤运动进行表征并创建治疗体积。将这些结果与标准治疗体积进行比较。
获取了10例患者的四维CT和自由呼吸螺旋CT数据。在螺旋扫描以及4D数据的每个相位上勾画大体肿瘤体积（GTV）。在4DCT上定义复合GTV。生成包括临床靶区体积、内部边界（IM）和摆位边界的计划靶区体积（PTV）。通过计算质心位置、体积、体积重叠和边界框，比较具有不同IM的4DPTV和标准PTV。
四维PTV和传统PTV在体积和质心位置上存在差异。仅从两个极端肿瘤位置生成的4DPTV与10个呼吸相位相比的重叠率为93.7%。将复合4D靶区体积上边界为15mm（IM为5mm）的PTV与螺旋CT数据上边界为20mm（IM为10mm）的PTV进行比较，结果平均靶区体积大小减少了23%。
通过对肿瘤运动进行患者特异性表征，应该有可能减少内部边界。可以使用4DCT上的极端肿瘤位置生成患者特异性治疗体积。迄今为止，已有超过150例患者采用4D靶区设计进行治疗。
