Department of Radiation Oncology Graduate School of Medicine, Juntendo University, Tokyo, Japan.
Department of Radiological Technology Faculty of Health Science, Juntendo University, Tokyo, Japan.
J Appl Clin Med Phys. 2021 Jul;22(7):93-102. doi: 10.1002/acm2.13271. Epub 2021 May 24.
Helical tomotherapy (HT) is a form of intensity-modulated radiation therapy that is employed in total body irradiation (TBI). Because TBI targets the whole body, accurate setup positioning at the edge of the treatment volume is made difficult by the whole-body rotational posture. The purpose of this study is to clarify the tolerance for rotational setup error (SE) in the vertical direction. In addition, we perform a retrospective analysis of actually irradiated dose distributions using previous patients' irradiation data.
To clarify the effects of rotational SE on the dose distribution, the planned CT images of 10 patients were rotated by 1-5° in the vertical (pitch) direction to create a pseudo-rotational SE image. Then, the effect of the magnitude of the rotational SE on the dose distribution was simulated. In addition, the irradiated dose to the patients was analyzed by obtaining recalculated dose distributions using megavoltage CT images acquired before treatment.
The simulation results showed that the average value of the lung volume receiving at least 10 Gy did not exceed the allowable value when the SE value was ≤2°. When the rotational SE was ≤3°, it was possible to maintain the clinical target volume dose heterogeneity within ±10% of the prescribed dose, which is acceptable according to the guidelines. A retrospective analysis of previous patients' irradiation data showed their daily irradiation dose distribution. The dose to the clinical target volume was reduced by up to 3.4% as a result of the residual rotational SE. Although whole-course retrospective analyses showed a statistically significant increase in high-dose areas, the increase was only approximately 1.0%.
Dose errors induced by rotational SEs of ≤2° were acceptable in this study.
螺旋断层放疗（HT）是调强放疗的一种形式，用于全身照射（TBI）。由于 TBI 针对全身，全身旋转姿势使得在治疗体积边缘进行准确的设置定位变得困难。本研究的目的是阐明在垂直方向上旋转设置误差（SE）的耐受度。此外，我们使用以前患者的照射数据对实际照射剂量分布进行回顾性分析。
为了阐明旋转 SE 对剂量分布的影响，将 10 名患者的计划 CT 图像在垂直（俯仰）方向上旋转 1-5°，以创建伪旋转 SE 图像。然后，模拟旋转 SE 大小对剂量分布的影响。此外，通过使用治疗前采集的兆伏 CT 图像获得重新计算的剂量分布来分析患者的照射剂量。
模拟结果表明，当 SE 值≤2°时，至少接收 10Gy 的肺体积的平均值不超过允许值。当旋转 SE≤3°时，能够保持临床靶区剂量不均匀性在规定剂量的±10%范围内，这是根据指南可接受的。对以前患者照射数据的回顾性分析显示了他们的日常照射剂量分布。由于残留的旋转 SE，临床靶区的剂量减少了最多 3.4%。虽然全疗程回顾性分析显示高剂量区域有统计学意义的增加，但增加仅约为 1.0%。
在本研究中，≤2°的旋转 SE 引起的剂量误差是可以接受的。
