The impact of fluctuations in intensity patterns on the number of monitor units and the quality and accuracy of intensity modulated radiotherapy
The impact of fluctuations in intensity patterns on the number of monitor units and the quality and accuracy of intensity modulated radiotherapy
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DOI：
10.1118/1.599000
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发表时间：
2000-06-01
期刊：
影响因子：
3.8
通讯作者：
Siebers, J
中科院分区：
文献类型：
--
作者：
Mohan, R;Arnfield, M;Siebers, J
这项工作的目的是检查强度调制放射治疗（IMRT）剂量分布的波动（“复杂性”）的频率和幅度的潜在影响。使用多叶准直器（MLC）有效地递送强度调制光束。辐射可以通过由叶片形成的连续（动态模式）或离散（步进和发射）窗口序列来递送。将优化的强度分布转换成叶轨迹的算法和软件应用近似的经验校正以考虑与MLC特性相关联的各种效应，诸如圆形叶尖、舌槽叶设计、叶透射、叶散射和MLC上游的准直器散射。通常，叶间和叶内传输之间的差异被忽略。在本文中，我们使用头颈部癌调强放射治疗的示意性示例，证明了复杂的解剖结构和严格的优化约束会产生复杂的强度模式。使用理想化的强度模式，我们还表明，对于复杂的强度模式，平均窗口宽度往往较小，并且对于肿瘤接受的相同剂量，MU的数量较大。我们发现，随着复杂性的增加，通过树叶传播和从树叶散射的辐射（“间接辐射”）对总传递剂量的贡献也增加。因此，复杂强度模式中的最低可递送强度可能显著大于为一些正常组织提供充分保护所需的强度。此外，由于叶透射和散射效应的校正是近似的，并且叶间透射和叶内透射之间的差异被忽略，因此递送剂量的准确性可能受到影响。使用一个简单的实验和一个典型的强度调制光束的头部和颈部的情况下作为例子的结果，我们显示的窗口宽度和复杂性的强度图案的准确性和可交付性的效果。讨论了提高精度和放宽可传递强度下限的一些可能策略。(C)2000年美国医学物理学家协会。【S0094-2405（00）00306-0】。
The purpose of this work is to examine the potential impact of the frequency and amplitude of fluctuations ("complexity") in intensity distributions on intensity-modulated radiotherapy (IMRT) dose distributions. The intensity-modulated beams are efficiently delivered using a multileaf collimator (MLC). Radiation may be delivered through a continuous (dynamic mode) or discrete (step-and-shoot) sequence of windows formed by the leaves. Algorithms and software that convert optimized intensity distributions into leaf trajectories apply approximate empirical corrections to account for the various effects associated with MLC characteristics, such as the rounded leaf tips, tongue-and-groove leaf design, leaf transmission, leaf scatter, and collimator scatter upstream from the MLC. Typically, the difference between inter- and intraleaf transmissions is ignored. In this paper, using a schematic example of IMRT for head and neck carcinomas, we demonstrate that complex anatomy and severe optimization constraints produce complex intensity patterns. Using idealized intensity patterns we also demonstrate that, for complex intensity patterns, the average window width tends to be smaller and, for the same dose received by the tumor, the number of MUs is larger. We found that as the complexity increases, so does the contribution of radiation transmitted through and scattered from the leaves ("indirect radiation") to the total delivered dose. As a consequence, the lowest deliverable intensity in complex intensity patterns may be significantly greater than that required to provide adequate protection for some normal tissues. Furthermore, since corrections for leaf transmission and scatter effects are approximate and the difference between inter- and intraleaf transmission is ignored, the accuracy of the delivered dose may be affected. Using the results of a simple experiment and a typical intensity-modulated beam for a head and neck case as examples, we show the effect of window width and complexity on the accuracy and deliverability of intensity patterns. Some possible strategies for improving the accuracy and for relaxing the lower limit on deliverable intensity are discussed. (C) 2000 American Association of Physicists in Medicine. [S0094-2405(00)00306-0].