Strydhorst Jared H, Caudrelier Jean-Michel, Clark Brenda G, Montgomery Lynn A, Fox Greg, MacPherson Miller S
The Ottawa Hospital Cancer Centre, Ottawa, Canada.
Med Dosim. 2011 Spring;36(1):81-4. doi: 10.1016/j.meddos.2010.01.001. Epub 2010 Mar 25.
We report on the impact of a thermoplastic immobilization system on intra- and interfraction motion for patients undergoing breast or chest wall radiation therapy. Patients for this study were treated using helical tomotherapy. All patients were immobilized using a thermoplastic shell extending from the shoulders to the ribcage. Intrafraction motion was assessed by measuring maximum displacement of the skin, heart, and chest wall on a pretreatment 4D computed tomography, while inter-fraction motion was inferred from patient shift data arising from daily image guidance procedures on tomotherapy. Using thermoplastic immobilization, the average maximum motion of the external contour was 1.3 ± 1.6 mm, whereas the chest wall was found to be 1.6 ± 1.9 mm. The day-to-day setup variation was found to be large, with random errors of 4.0, 12.0, and 4.5 mm in the left-right, superior-inferior, and anterior-posterior directions, respectively, and the standard deviations of the systematic errors were found to be 2.7, 9.8, and 4.1 mm. These errors would be expected to dominate any respiratory motion but can be mitigated by daily online image guidance. Using thermoplastic immobilization can effectively reduce respiratory motion of the chest wall and external contour, but these gains can only be realized if daily image guidance is used.
我们报告了热塑性固定系统对接受乳房或胸壁放射治疗患者的分次内及分次间运动的影响。本研究中的患者采用螺旋断层放射治疗。所有患者均使用从肩部延伸至胸廓的热塑性外壳进行固定。通过在治疗前的4D计算机断层扫描上测量皮肤、心脏和胸壁的最大位移来评估分次内运动，而分次间运动则从断层放射治疗每日图像引导程序产生的患者移位数据中推断得出。使用热塑性固定时，外部轮廓的平均最大运动为1.3±1.6毫米，而胸壁的平均最大运动为1.6±1.9毫米。发现每日设置变化较大，在左右、上下和前后方向上的随机误差分别为4.0、12.0和4.5毫米，系统误差的标准差分别为2.7、9.8和4.1毫米。预计这些误差将主导任何呼吸运动，但可通过每日在线图像引导来减轻。使用热塑性固定可有效减少胸壁和外部轮廓的呼吸运动，但只有在使用每日图像引导的情况下才能实现这些效果。
