Department of Radiation Oncology, William Beaumont Hospital, Royal Oak, MI, USA.
Int J Radiat Oncol Biol Phys. 2010 Jul 1;77(3):910-7. doi: 10.1016/j.ijrobp.2009.09.080.
To evaluate intra- and interfraction variability of tumor and lung volume and position using a hybrid active breath-hold gating technique.
A total of 159 repeat normal inspiration active breath-hold CTs were acquired weekly during radiotherapy for 9 lung cancer patients (12-21 scans per patient). A physician delineated the gross tumor volume (GTV), lungs, and spinal cord on the first breath-hold CT, and contours were propagated semiautomatically. Intra- and interfraction variability of tumor and lung position and volume were evaluated. Tumor centroid and border variability were quantified.
On average, intrafraction variability of lung and GTV centroid position was <2.0 mm. Interfraction population variability was 3.6-6.7 mm (systematic) and 3.1-3.9 mm (random) for the GTV centroid and 1.0-3.3 mm (systematic) and 1.5-2.6 mm (random) for the lungs. Tumor volume regressed 44.6% +/- 23.2%. Gross tumor volume border variability was patient specific and demonstrated anisotropic shape change in some subjects. Interfraction GTV positional variability was associated with tumor volume regression and contralateral lung volume (p < 0.05). Inter-breath-hold reproducibility was unaffected by time point in the treatment course (p > 0.1). Increases in free-breathing tidal volume were associated with increases in breath-hold ipsilateral lung volume (p < 0.05).
The breath-hold technique was reproducible within 2 mm during each fraction. Interfraction variability of GTV position and shape was substantial because of tumor volume and breath-hold lung volume change during therapy. These results support the feasibility of a hybrid breath-hold gating technique and suggest that online image guidance would be beneficial.
使用混合主动屏气门控技术评估肿瘤和肺体积及位置的分次内和分次间变异性。
对 9 例肺癌患者的放疗过程中每周进行 159 次重复的常规吸气主动屏气 CT 扫描（每位患者 12-21 次扫描）。一位医生在第一次屏气 CT 上勾画大体肿瘤体积（GTV）、肺和脊髓，并半自动传播轮廓。评估肿瘤和肺位置及体积的分次内和分次间变异性。量化肿瘤中心和边界的变异性。
平均而言，肺和 GTV 中心位置的分次内变异性<2.0mm。群体间变异性为 3.6-6.7mm（系统误差）和 3.1-3.9mm（随机误差），用于 GTV 中心位置，1.0-3.3mm（系统误差）和 1.5-2.6mm（随机误差）用于肺部。肿瘤体积回缩了 44.6%±23.2%。GTV 边界变异性具有个体特异性，一些患者显示出各向异性的形状变化。GTV 位置的分次间变异性与肿瘤体积回缩和对侧肺体积相关（p<0.05）。呼吸暂停期间，在治疗过程中的不同时间点，呼吸暂停的可重复性不受影响（p>0.1）。自由呼吸潮气量的增加与屏气时同侧肺体积的增加相关（p<0.05）。
在每次屏气期间，屏气技术的可重复性为 2mm 以内。由于治疗过程中肿瘤体积和屏气肺体积的变化，GTV 位置和形状的分次间变异性很大。这些结果支持混合屏气门控技术的可行性，并表明在线图像引导将是有益的。
