How much margin reduction is possible through gating or breath hold?
How much margin reduction is possible through gating or breath hold?
复制标题
DOI：
10.1088/0031-9155/50/3/006
复制
发表时间：
2005-02-07
影响因子：
3.5
通讯作者：
Shirato, H
中科院分区：
文献类型：
--
作者：
Engelsman, M;Sharp, GC;Shirato, H
我们使用北海道大学放射外科治疗的40例患者（43个肿瘤部位）的每日实时肿瘤跟踪数据，确定了分次呼吸运动与安全范围之间的关系。我们将我们的研究限制在分数内呼吸运动的剂量模糊效应，并且没有考虑定位精度或系统误差的差异。通过将一维剂量分布与呼吸的概率密度函数（PDF）进行卷积来确定规定等剂量水平（例如95%）的额外偏移，一维剂量分布具有代表通过肺或水的8 MV射束的剂量梯度。这种额外的偏移是为了保持与不使用分次呼吸时相同的肿瘤控制概率而应应用的额外裕度的量度。我们表明，所需的安全裕度是一个非线性函数的峰-峰呼吸运动。只有一个小的减少等剂量曲线的移位观察到呼吸运动高达10 mm。对于较大的运动，20或30 mm，控制患者的呼吸在照射过程中，使用门控或屏气，可以允许一个大幅度减少约7或12 mm的安全裕度，这取决于剂量梯度之前虚张声势。临床相关的随机设置不确定性，也对剂量分布有模糊影响，对分次呼吸运动所需的裕度只有很小的影响。由于我们分析的一维性质，所得的边缘主要适用于上下方向。大多数测量的呼吸PDF与简单参数曲线（如cos（4））的PDF不一致，这是因为呼吸不规则或基线偏移。相反，我们的分析表明，呼吸运动可以被建模为高斯，其标准偏差约为峰到峰呼吸运动的0.4倍。
We determined the relationship between intra-fractional breathing motion and safety margins, using daily real-time tumour tracking data of 40 patients (43 tumour locations), treated with radiosurgery at Hokkaido University. We limited our study to the dose-blurring effect of intra-fractional breathing motion, and did not consider differences in positioning accuracy or systematic errors. The additional shift in the prescribed isodose level (e.g. 95%) was determined by convolving a one-dimensional dose profile, having a dose gradient representing an 8 MV beam through either lung or water, with the probability density function (PDF) of breathing. This additional shift is a measure for the additional margin that should be applied in order to maintain the same probability of tumour control as without intra-fractional breathing. We show that the required safety margin is a nonlinear function of the peak-to-peak breathing motion. Only a small reduction in the shift of isodose curves was observed for breathing motion up to 10 mm. For larger motion, 20 or 30 mm, control of patient breathing during irradiation, using either gating or breath hold, can allow a substantial reduction in safety margins of about 7 or 12 mm depending on the dose gradient prior to bluffing. Clinically relevant random setup uncertainties, which also have a blurring effect on the dose distribution, have only a small effect on the margin needed for intra-fractional breathing motion. Because of the one-dimensional nature of our analysis, the resulting margins are mainly applicable in the superior-inferior direction. Most measured breathing PDFs were not consistent with the PDF of a simple parametric curve such as cos(4), either because of irregular breathing or base-line shifts. Instead, our analysis shows that breathing motion can be modelled as Gaussian with a standard deviation of about 0.4 times the peak-to-peak breathing motion.