Remouchamps Vincent M, Letts Nicola, Yan Di, Vicini Frank A, Moreau Michel, Zielinski Julie A, Liang Jian, Kestin Larry L, Martinez Alvaro A, Wong John W
Department of Radiation Oncology, William Beaumont Hospital, Royal Oak, MI 48073, USA.
Int J Radiat Oncol Biol Phys. 2003 Nov 15;57(4):968-78. doi: 10.1016/s0360-3016(03)00710-7.
A CT-based three-dimensional (3D) method was used to analyze the intra- and interfraction reproducibility of lung immobilization during moderate deep inspiration breath hold (mDIBH), defined as 75% of the maximal inspiration using an active breathing control (ABC) apparatus.
The ABC apparatus was used to immobilize the breathing motion with a computer-controlled valve. Immobilization of the lungs in breast cancer patients was used as a model to evaluate the reproducibility of mDIBH using the ABC apparatus. CT scans were acquired twice at mDIBH in the same session for 30 breast cancer patients. Twenty-three of them were immobilized with an alpha-cradle, of which 14 had a repeat scan at mDIBH 1-4 weeks later. Twelve of those patients received intensity-modulated radiotherapy to the left breast at mDIBH to displace the heart from the beam. The remaining patients were treated at free breathing, with either intensity-modulated irradiation to the whole breast or conformal partial breast irradiation. To remove the component of setup error, mDIBH scans were registered with respect to the vertebrae. The lungs and carina were auto-contoured to form 3D surfaces for each data set. The closest distance-to-agreement (DTA) for each point between the 3D surfaces of the corresponding CT scans was displayed on a 3D surface map. For analysis, each lung was divided along its inferior to superior extent into six regions, from the basal 10%, the next four consecutive 20% sections in height, to the last apical 10%. Likewise, the carina was divided into regions of the trachea and bifurcation. The mean and standard deviation (SD) of the DTA for each of these regions was computed.
With the patient positioned in an alpha-cradle, the mean +/- SD intrafraction DTA was 1.5 +/- 1.4 mm for the left lung and 1.0 +/- 1.4 mm for the right lung. The corresponding values without the use of an alpha-cradle were significantly greater, with 1.9 +/- 2.1 mm and 2.2 +/- 2.2 mm for the left and right lung, respectively (p <0.005 for the SD of the left lung and p <0.0003 for the SD of the right lung). The interfraction DTA for the left and right lungs was 1.4 +/- 1.7 mm and 1.4 +/- 1.6 mm, respectively. The regional analysis demonstrated better immobilization for the upper two-thirds of the chest wall compared with that for the lung base. The DTA values obtained for the tracheal bifurcation were 0.9 +/- 0.8 mm for intrafraction and 1.4 +/- 1.0 mm for interfraction.
The ABC device can be used to reduce respiratory motion at mDIBH in breast cancer patients or those patients who can perform the maneuver. This device demonstrated excellent intra- and interfraction reproducibility of chest wall and carina immobilization, especially when combined with alpha-cradle immobilization. Internal margins for suspended breathing can be extrapolated from these data for various anatomic regions within the lung and chest wall.
采用基于CT的三维（3D）方法分析在适度深吸气屏气（mDIBH）期间肺固定的分次内和分次间可重复性，mDIBH定义为使用主动呼吸控制（ABC）装置达到最大吸气量的75%。
使用ABC装置通过计算机控制的阀门固定呼吸运动。以乳腺癌患者的肺固定作为模型，评估使用ABC装置时mDIBH的可重复性。在同一疗程中，对30例乳腺癌患者在mDIBH时进行两次CT扫描。其中23例使用α型托架固定，其中14例在1 - 4周后于mDIBH时进行重复扫描。这些患者中有12例在mDIBH时接受了左侧乳腺的调强放疗，以使心脏移出射野。其余患者在自由呼吸状态下接受全乳调强照射或适形部分乳腺照射。为消除摆位误差成分，将mDIBH扫描图像与椎体进行配准。对每个数据集自动勾勒出肺和隆突以形成3D表面。在3D表面图上显示相应CT扫描的3D表面之间每个点的最接近一致性距离（DTA）。为进行分析，将每个肺从下到上沿其范围分为六个区域，从基底的10%，接下来四个连续高度为20%的节段，到最后的尖段10%。同样，将隆突分为气管和分叉区域。计算这些区域中每个区域的DTA的平均值和标准差（SD）。
患者置于α型托架中时，左侧肺的分次内DTA平均值±SD为1.5±1.4mm，右侧肺为1.0±1.4mm。未使用α型托架时的相应值明显更大，左侧肺和右侧肺分别为1.9±2.1mm和2.2±2.2mm（左侧肺SD的p<0.005，右侧肺SD的p<0.0003）。左侧和右侧肺的分次间DTA分别为1.4±1.7mm和1.4±1.6mm。区域分析表明，胸壁上三分之二的固定效果优于肺底部。气管分叉处的分次内DTA值为0.9±0.8mm，分次间为1.4±-1.0mm。
ABC装置可用于减少乳腺癌患者或能够进行该操作的患者在mDIBH时的呼吸运动。该装置在胸壁和隆突固定方面显示出优异的分次内和分次间可重复性，尤其是与α型托架固定相结合时。可从这些数据推断出肺和胸壁内各个解剖区域在屏气时的内部边界。
