Tolerances on MLC leaf position accuracy for IMRT delivery with a dynamic MLC
Tolerances on MLC leaf position accuracy for IMRT delivery with a dynamic MLC
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DOI：
10.1118/1.3134244
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发表时间：
2009-07-01
期刊：
影响因子：
3.8
通讯作者：
Dunscombe, Peter
中科院分区：
文献类型：
--
作者：
Rangel, Alejandra;Dunscombe, Peter
理想情况下，客观确定放射治疗设备的性能标准需要建立性能偏差与临床结果或某种可接受的替代品之间的定量关系。在该模拟研究中，作者分析了MLC叶片位置的随机（逐叶）和系统（整个叶片库）误差对使用动态MLC提供的7个临床前列腺和7个临床头颈部IMRT计划的剂量影响。开发了内部软件，以将单个叶片位置的正态分布误差（最高+/- 2 mm）或系统误差（两个叶片库的所有叶片均为+/- 1和+/- 0.5 mm，或仅一个叶片库为+1 mm）纳入14个计划中，从而使用次优性能MLC模拟治疗输送。使用临床靶体积和重要危及器官（OAR）的等效均匀剂量（EUD）量化次优MLC性能的剂量学后果。MLC性能恶化时所选结构的EUD偏差用作临床结局的客观替代。2 mm的随机误差导致两个站点中所有感兴趣结构的变化可忽略不计。相比之下，系统误差可能导致潜在的显著剂量变化，从而可能影响临床结果。如果目标EUD和OAR的2戈伊变化为2%，则由于MLC效应单独作为剂量偏差的可接受水平，则叶位置的系统误差将需要限制在0.3 mm。本研究提供了指导，基于临床结果的剂量替代，用于开发一个组件，多叶准直器性能标准的叶位置准确度。
The objective determination of performance standards for radiation therapy equipment requires, ideally, establishing the quantitative relationship between performance deviations and clinical outcome or some acceptable surrogate. In this simulation study the authors analyzed the dosimetric impact of random (leaf by leaf) and systematic (entire leaf bank) errors in the position of the MLC leaves on seven clinical prostate and seven clinical head and neck IMRT plans delivered using a dynamic MLC. In-house software was developed to incorporate normally distributed errors of up to +/- 2 mm in individual leaf position or systematic errors (+/- 1 and +/- 0.5 mm in all leaves of both leaf banks or +1 mm in one bank only) into the 14 plans, thus simulating treatment delivery using a suboptimally performing MLC. The dosimetric consequences of suboptimal MLC performance were quantified using the equivalent uniform doses (EUDs) of the clinical target volumes and important organs at risk (OARs). The deviation of the EUDs of the selected structures as the performance of the MLC deteriorated was used as the objective surrogate of clinical outcome. Random errors of 2 mm resulted in negligible changes for all structures of interest in both sites. In contrast, systematic errors can lead to potentially significant dosimetric changes that may compromise clinical outcome. If a 2% change in EUD of the target and 2 Gy for the OARs were adopted as acceptable levels of deviation in dose due to MLC effects alone, then systematic errors in leaf position will need to be limited to 0.3 mm. This study provides guidance, based on a dosimetric surrogate of clinical outcome, for the development of one component, leaf position accuracy of performance standards for multileaf collimators.