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首页> 外文期刊>Radiotherapy and oncology: Journal of the European Society for Therapeutic Radiology and Oncology >The effect of breathing and set-up errors on the cumulative dose to a lung tumor.
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The effect of breathing and set-up errors on the cumulative dose to a lung tumor.

机译：呼吸和设置错误对肺部肿瘤累积剂量的影响。

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BACKGROUND AND PURPOSE: To assess the impact of both set-up errors and respiration-induced tumor motion on the cumulative dose delivered to a clinical target volume (CTV) in lung, for an irradiation based on current clinically applied field sizes. MATERIALS AND METHODS: A cork phantom, having a 50 mm spherically shaped polystyrene insertion to simulate a gross tumor volume (GTV) located centrally in a lung was irradiated with two parallel opposed beams. The planned 95% isodose surface was conformed to the planning target volume (PTV) using a multi leaf collimator. The resulting margin between the CTV and the field edge was 16 mm in beam's eye view. A dose of 70 Gy was prescribed. Dose area histograms (DAHs) of the central plane of the CTV (GTV+5 mm) were determined using radiographic film for different combinations of set-up errors and respiration-induced tumor motion. The DAHs were evaluated using the population averaged tumor control probability (TCP(pop)) and the equivalent uniform dose (EUD) model. RESULTS: Compared with dose volume histograms of the entire CTV, DAHs overestimate the impact of tumor motion on tumor control. Due to the choice of field sizes a large part of the PTV will receive a too low dose resulting in an EUD of the central plane of the CTV of 68.9 Gy for the static case. The EUD drops to 68.2, 66.1 and 51.1 Gy for systematic set-up errors of 5, 10 and 15 mm, respectively. For random set-up errors of 5, 10 and 15 mm (1 SD), the EUD decreases to 68.7, 67.4 and 64.9 Gy, respectively. For similar amplitudes of respiration-induced motion, the EUD decreases to 68.8, 68.5 and 67.7 Gy, respectively. For a clinically relevant scenario of 7.5 mm systematic set-up error, 3 mm random set-up error and 5 mm amplitude of breathing motion, the EUD is 66.7 Gy. This corresponds with a tumor control probability TCP(pop) of 41.7%, compared with 50.0% for homogeneous irradiation of the CTV to 70 Gy. CONCLUSION: Systematic set-up errors have a dominant effect on the cumulative dose to the CTV. The effect of breathing motion and random set-up errors is smaller. Therefore the gain of controlling breathing motion during irradiation is expected to be small and efforts should rather focus on minimizing systematic errors. For the current clinically applied field sizes and a clinically relevant combination of set-up errors and breathing motion, the EUD of the central plane of the CTV is reduced by 3.3 Gy, at maximum, relative to homogeneous irradiation of the CTV to 70 Gy, for our worst case scenario.
机译：背景和目的：基于当前临床应用的视野大小，评估设置误差和呼吸诱导的肿瘤运动对递送至肺部临床目标体积（CTV）的累积剂量的影响。材料与方法：用两个平行的相对光束照射一个具有50 mm球形聚苯乙烯插入物以模拟位于肺中央的总肿瘤体积（GTV）的软木模型。使用多叶准直仪将计划的95％的等剂量面与计划目标体积（PTV）保持一致。在光束的视线范围内，CTV和场边缘之间的余量为16 mm。规定剂量为70 Gy。使用X射线胶片确定CTV中央平面（GTV + 5 mm）的剂量区域直方图（DAHs），用于设置误差和呼吸诱导的肿瘤运动的不同组合。使用人群平均肿瘤控制概率（TCP（pop））和等效均匀剂量（EUD）模型评估DAH。结果：与整个CTV的剂量体积直方图相比，DAHs高估了肿瘤运动对肿瘤控制的影响。由于场大小的选择，PTV的很大一部分将接受太低的剂量，导致静态情况下CTV中心平面的EUD为68.9 Gy。对于5、10和15毫米的系统设置误差，EUD分别降至68.2、66.1和51.1 Gy。对于5、10和15毫米（1 SD）的随机设置误差，EUD分别降至68.7、67.4和64.9 Gy。对于由呼吸引起的运动的类似幅度，EUD分别降至68.8、68.5和67.7 Gy。对于7.5 mm系统设置误差，3 mm随机设置误差和5 mm呼吸运动幅度的临床相关情况，EUD为66.7 Gy。这对应于41.7％的肿瘤控制概率TCP（pop），而将CTV均匀照射到70 Gy则为50.0％。结论：系统设置错误对CTV的累积剂量起主要作用。呼吸运动和随机设置错误的影响较小。因此，预期在辐照期间控制呼吸运动的增益很小，而应该将精力集中在最小化系统误差上。对于当前临床应用的视野大小以及设置错误和呼吸运动的临床相关组合，相对于CTV的均匀照射到70 Gy，CTV中央平面的EUD最大减少了3.3 Gy，对于我们最坏的情况。

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