Aznar Marianne C, Persson Gitte F, Kofoed Inger M, Nygaard Ditte E, Korreman Stine S
Department of Radiation Oncology, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark; Niels Bohr Institute, Faculty of Sciences, University of Copenhagen, Denmark.
Department of Radiation Oncology, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark.
Phys Med. 2014 Feb;30(1):69-75. doi: 10.1016/j.ejmp.2013.03.003. Epub 2013 Apr 13.
With 4DCT the risk of introducing positional systematic errors in lung cancer radiotherapy can be minimised. A common approach is to plan on the phase bin of the 4DCT best representing the tumour's time-weighted mean position also called the midventilation scan. However breathing irregularities can introduce uncertainties and potentially misrepresent both the tumour trajectory and the determination of the midventilation phase. In this study we evaluated the robustness of the midventilation approach in the presence of irregular breathing patterns.
A LEGO Mindstorms(®) phantom with compact balls simulating lung tumours was constructed. The breathing curves loaded in the phantom were either acquired from a human volunteer or constructed with various magnitudes (ranging from 12 to 29 mm) as well as various irregularities of motion pattern. Repeated 4DCT scans were performed while tumour trajectories were recorded with two motion tracking systems.
The time-weighted mean tumour position is accurately represented in 4DCT scans, even for irregular breathing patterns: the position presentation in the midventilation scan was always within in one standard deviation of the global position presentation (3 mm and 2 mm for regular and irregular breathing patterns, respectively). The displacement representation tended to be underestimated in 4DCT scans.
The midventilation approach is robust even in the presence of breathing irregularity. The representation of the tumour trajectory in 4DCT scans is affected by breathing irregularity and the extent of tumour motion can be underestimated, which will affect the calculation of patient-individualised margins based on the 4DCT scan.
使用4DCT可将肺癌放疗中引入位置系统误差的风险降至最低。一种常见的方法是在4DCT的相位区间上进行计划，该区间最能代表肿瘤的时间加权平均位置，也称为中期通气扫描。然而，呼吸不规则会引入不确定性，并可能错误地呈现肿瘤轨迹和中期通气阶段的判定。在本研究中，我们评估了在存在不规则呼吸模式的情况下中期通气方法的稳健性。
构建了一个带有模拟肺肿瘤的紧凑型球的乐高头脑风暴（®）模型。加载到模型中的呼吸曲线要么是从一名人类志愿者身上获取的，要么是构建的，具有各种幅度（范围从12到29毫米）以及各种运动模式的不规则性。在使用两个运动跟踪系统记录肿瘤轨迹的同时，进行重复的4DCT扫描。
即使对于不规则呼吸模式，4DCT扫描中也能准确呈现时间加权平均肿瘤位置：中期通气扫描中的位置呈现始终在全局位置呈现的一个标准差范围内（规则和不规则呼吸模式分别为3毫米和2毫米）。4DCT扫描中的位移呈现往往被低估。
即使存在呼吸不规则，中期通气方法也是稳健的。4DCT扫描中肿瘤轨迹的呈现受呼吸不规则影响，肿瘤运动程度可能被低估，这将影响基于4DCT扫描的个体化边界的计算。
