Takenaka Ryosuke, Haga Akihiro, Yamashita Hideomi, Nakagawa Keiichi
Department of Radiology, University of Tokyo Hospital, 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113-8655, Japan.
J Radiat Res. 2017 Mar 1;58(2):210-216. doi: 10.1093/jrr/rrw115.
Recently, intensity-modulated radiation therapy (IMRT) has been used for total-body irradiation (TBI). Since the planning target volume (PTV) for TBI includes the surrounding air, a dose prescription to the PTV provides high fluence to the body surface. Thus with just a small set-up error, the body might be exposed to a high-fluence beam. This study aims to assess which target volume should be prescribed the dose, such as a clinical target volume (CTV) with a margin, or a CTV that excludes the surface area of the skin. Three treatment plans were created for each patient: the 5-mm clipped plan (Plan A), the 0-mm margin plan (Plan B) and the 5-mm margin plan (Plan C). The CTV was the whole body. PTVs were the CTV with the exception of 5 mm from the skin surface in Plan A, equal to the CTV in Plan B, and the CTV with a 5 mm margin in Plan C. The prescribed dose was 12 Gy in six fractions. To assess the influence of the set-up error, dose distributions were simulated on computed tomography (CT) images shifted 2 pixels (= 4.296 mm), 5 pixels (= 10.74 mm) and 10 pixels (= 21.48 mm) in the lateral direction from the original CT. With a set-up error of 10.74 mm, V110% was 8.8%, 11.1% and 23.3% in Plans A, B and C, respectively. The prescription to the PTV containing the surrounding air can be paradoxically vulnerable to a high-dose as a consequence of a small set-up error.
最近，调强放射治疗（IMRT）已被用于全身照射（TBI）。由于TBI的计划靶体积（PTV）包括周围空气，对PTV的剂量处方会在体表产生高注量。因此，只要有很小的摆位误差，身体就可能暴露于高注量射束下。本研究旨在评估应向哪个靶体积处方剂量，例如带有边界的临床靶体积（CTV），还是排除皮肤表面积的CTV。为每位患者创建了三个治疗计划：5毫米裁剪计划（计划A）、0毫米边界计划（计划B）和5毫米边界计划（计划C）。CTV为全身。PTV在计划A中是除皮肤表面5毫米外的CTV，在计划B中等于CTV，在计划C中是带有5毫米边界的CTV。处方剂量为12 Gy，分六次给予。为评估摆位误差的影响，在从原始CT图像横向移位2像素（= 4.296毫米）、5像素（= 10.74毫米）和10像素（= 21.48毫米）的计算机断层扫描（CT）图像上模拟剂量分布。当摆位误差为10.74毫米时，计划A、B和C中的V110%分别为8.8%、11.1%和23.3%。包含周围空气的PTV处方可能因小的摆位误差而反常地易受高剂量影响。
