What is the optimum leaf width of a multileaf collimator?
What is the optimum leaf width of a multileaf collimator?
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DOI：
10.1118/1.1319524
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发表时间：
2000-11-01
期刊：
影响因子：
3.8
通讯作者：
Nill, S
中科院分区：
文献类型：
--
作者：
Bortfeld, T;Oelfke, U;Nill, S
研究以下问题：多叶准直器的叶片必须有多窄，使得叶片宽度的进一步减小不会导致剂量分布的物理改善。由于辐射与物质相互作用的物理原理，放射治疗中的剂量分布一般都比较平滑。根据采样理论，剂量分布可以用一组均匀间隔的样本来表示。样本之间的距离通过多叶准直器的叶中心之间的距离来确定。最佳采样距离是通过剂量沉积核的概念从20%至80%场边缘半影推导出来的，其近似为高斯。多叶准直器的叶宽被认为与采样距离无关。详细研究了两种情况：（i）叶子宽度等于采样距离，这是常规情况，以及（ii）叶子宽度是采样距离的两倍。后一种治疗几何形状的实际实施需要治疗床移动或准直器旋转。对于软组织中典型的 6 MV 光束，最佳采样距离等于 20%-80% 半影除以 1.7，约为 1.5-2 mm。在常规情况下，最佳叶宽等于该采样距离。如果叶宽加倍，而采样距离保持不变，则会产生相对较小的恶化。可以通过使用逆倾斜器对注量分布进行去卷积来校正恶化。结论：借助采样理论以及更一般的线性系统理论，人们可以从物理角度找到多叶准直器最佳叶宽问题的通用答案。区分采样距离和叶宽很重要。采样距离比叶宽更重要。叶宽度最多可以是采样宽度的两倍。此外，得出的采样距离可用于在剂量计算和逆规划算法中选择注量和剂量网格的最佳分辨率。 (C) 2000 年美国医学物理学家协会。 [S0094-2405 (00)02011-3]。
The following question is investigated: How narrow do the leaves of a multileaf collimator have to be such that further reduction of the leaf width does not lead to physical improvements of the dose distribution. Because of the physical principles of interaction between radiation and matter, dose distributions in radiotherapy are generally relatively smoothe According to the theory of sampling, the dose distribution can therefore be represented by a set of evenly spaced samples. The distance between the samples is identified with the distance between the leaf centers of a multileaf collimator. The optimum sampling distance is derived from the 20% to 80% field edge penumbra through the concept of the dose deposition kernel, which is approximated by a Gaussian. The leaf width of the multileaf collimator is considered to be independent from the sampling distance. Two cases are studied in detail: (i) the leaf width equals the sampling distance, which is the regular case, and (ii) the leaf width is twice the sampling distance. The practical delivery of the latter treatment geometry requires a couch movement or a collimator rotation. The optimum sampling distance equals the 20%-80% penumbra divided by 1.7 and is on the order of 1.5-2 mm for a typical 6 MV beam in soft tissue. The optimum leaf width equals this sampling distance in the regular case. A relatively small deterioration results if the leaf width is doubled, while the sampling distance remains the same. The deterioration can be corrected for by deconvolving the fluence profile with an inverse tilter. Conclusions: With the help of the sampling theory and, more generally, the theory of linear systems, one can find a general answer to the question about the optimum leaf width of a multileaf collimator from a physical point of view. It is important to distinguish between the sampling distance and the leaf width. The sampling distance is more critical than the leaf width. The leaf width can be up to twice as large as the sampling width. Furthermore, the derived sampling distance can be used to select the optimum resolution of both the fluence and the dose grid in dose calculation and inverse planning algorithms. (C) 2000 American Association of Physicists in Medicine. [S0094-2405 (00)02011-3].