Department of Medical Physics, University of Wisconsin-Madison, Madison, WI 53705, USA.
Phys Med Biol. 2010 May 21;55(10):2983-95. doi: 10.1088/0031-9155/55/10/012. Epub 2010 Apr 30.
The aim of the study was to demonstrate a potential alternative scenario for accurate dose-painting (non-homogeneous planned dose) delivery at 1 cm beam width with helical tomotherapy (HT) in the presence of 1 cm, three-dimensional, intra-fraction respiratory motion, but without any active motion management. A model dose-painting experiment was planned and delivered to the average position (proper phase of a 4DCT scan) with three spherical PTV levels to approximate dose painting to compensate for hypothetical hypoxia in a model lung tumor. Realistic but regular motion was produced with the Washington University 4D Motion Phantom. A small spherical Virtual Water phantom was used to simulate a moving lung tumor inside of the LUNGMAN anthropomorphic chest phantom to simulate realistic heterogeneity uncertainties. A piece of 4 cm Gafchromic EBT film was inserted into the 6 cm diameter sphere. TomoTherapy, Inc., DQA software was used to verify the delivery performed on a TomoTherapy Hi-Art II device. The dose uncertainty in the purposeful absence of motion management and in the absence of large, low frequency drifts (periods greater than the beam width divided by the couch velocity) or randomness in the breathing displacement yields very favorable results. Instead of interference effects, only small blurring is observed because of the averaging of many breathing cycles and beamlets and the avoidance of interference. Dose painting during respiration with helical tomotherapy is feasible in certain situations without motion management. A simple recommendation is to make respiration as regular as possible without low frequency drifting. The blurring is just small enough to suggest that it may be acceptable to deliver without motion management if the motion is equal to the beam width or smaller (at respiration frequencies) when registered to the average position.
本研究旨在展示一种潜在的替代方案，即在存在 1 厘米、三维、分次内呼吸运动的情况下，使用螺旋断层放疗（HT）以 1 厘米束宽实现精确的剂量涂漆（非均匀计划剂量），而无需任何主动的运动管理。计划并交付了一个模型剂量涂漆实验，该实验在平均位置（4DCT 扫描的适当相位）进行，使用三个球形 PTV 水平来近似剂量涂漆，以补偿模型肺肿瘤中的假设缺氧。使用华盛顿大学 4D 运动体模产生了现实但规则的运动。使用小的球形 Virtual Water 体模模拟移动的肺肿瘤，放置在 LUNGMAN 人体胸部体模内，以模拟现实的异质性不确定性。将一块 4 厘米厚的 Gafchromic EBT 胶片插入 6 厘米直径的球体中。使用 TomoTherapy，Inc.，DQA 软件验证在 TomoTherapy Hi-Art II 设备上执行的交付。在没有运动管理的情况下，以及在没有大的低频漂移（大于束宽除以治疗床速度的周期）或呼吸位移中的随机性的情况下，目的是消除剂量不确定性，结果非常有利。由于对许多呼吸周期和射束的平均化以及对干扰的避免，而不是干扰效应，仅观察到微小的模糊。在没有运动管理的情况下，使用螺旋断层放疗进行呼吸剂量涂漆在某些情况下是可行的。一个简单的建议是使呼吸尽可能规则，而不会出现低频漂移。模糊程度很小，足以表明在运动与束宽相等或更小时（在呼吸频率下），在平均位置注册时，无需运动管理即可接受。
