A comparison of the dosimetric effects of intrafraction motion on step-and-shoot, compensator, and helical tomotherapy-based IMRT
A comparison of the dosimetric effects of intrafraction motion on step-and-shoot, compensator, and helical tomotherapy-based IMRT
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DOI：
10.1120/jacmp.v14i3.4210
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发表时间：
2013-01-01
影响因子：
2.1
通讯作者：
Langen, Katja M.
中科院分区：
文献类型：
--
作者：
Waghorn, Ben J.;Staton, Robert J.;Langen, Katja M.
调强放射治疗期间的分次内运动可能导致计划剂量和输送患者剂量之间的差异。这些差异的大小取决于许多变量，包括治疗方式。本研究旨在比较使用三种不同治疗方式生成的计划对分次内运动的相对敏感性。运动的剂量学效应计算使用计算算法为7例肺肿瘤患者。研究了三种输送技术-基于MLC的步进式（SNS）、光束衰减补偿器和螺旋断层治疗（HT）。在总共840运动编码的剂量体积直方图（DVH）计算的各种组合的CTV边缘和正弦CTV运动，包括CTV偏移。基于DVH的度量（例如，D-95%和D-05%）用于对计划降级进行评分。对于所有三种模式，如果CTV位移小于CTV裕度，则剂量测定降解通常小于3%。对于较大的位移，存在技术和方向特定的敏感性。虽然HT计划在SI和AP方向上的运动显示出类似的D95%降级，但SNS和补偿器计划在SI方向上的运动显示出比在AP方向上的运动更大的D95%降级。当在所有运动/边缘组合上取平均值时，补偿器计划与SNS和HT计划相比分别导致D95%减小0.9%和0.6%。这些差异具有统计学显著性。对于所有边缘和运动轨迹组合的平均数据，SNS和HT之间的D95%退化没有统计学显著差异。对于大于CTV边界的CTV运动，对CTV的剂量影响因治疗技术和运动方向而异。对于本文所述的病例，补偿器输送的运动对CTV剂量测定的影响在统计学上小于SNS和HT，这可能是由于缺乏更动态治疗输送的相互作用效应。然而，模式之间的差异很小，可能没有临床意义。正如预期的那样，包围CTV运动的边缘为所有三种模式提供了针对运动的剂量测定保护。
Intrafraction motion during intensity-modulated radiation therapy can cause differences between the planned and delivered patient dose. The magnitude of these differences is dependent on a number of variables, including the treatment modality. This study was designed to compare the relative susceptibility of plans generated with three different treatment modalities to intrafraction motion. The dosimetric effects of motion were calculated using computational algorithms for seven lung tumor patients. Three delivery techniques - MLC-based step-and-shoot (SNS), beam attenuating compensators, and helical tomotherapy (HT) - were investigated. In total 840 motion-encoded dose-volume histograms (DVHs) were calculated for various combinations of CTV margins and sinusoidal CTV motion including CTV offsets. DVH-based metrics (e.g., D-95% and D-05%) were used to score plan degradations. For all three modalities, dosimetric degradations were typically smaller than 3% if the CTV displacement was smaller than the CTV margin. For larger displacements, technique and direction-specific sensitivities existed. While the HT plans show similar D95% degradations for motion in the SI and AP directions, SNS and compensator plans showed larger D95% degradations for motion in the SI direction than for motion in the AP direction. When averaged over all motion/margin combinations, compensator plans resulted in 0.9% and 0.6% smaller D95% reductions compared to SNS and HT plans, respectively. These differences were statistically significant. No statistically significant differences in D95% degradations were found between SNS and HT for data averaged over all margin and motion track combinations. For CTV motion that is larger than the CTV margin, the dosimetric impact on the CTV varies with treatment technique and the motion direction. For the cases presented here, the effect of motion on CTV dosimetry was statistically smaller for compensator deliveries than SNS and HT, likely due to the absence of the interplay effect which is present for the more dynamic treatment deliveries. The differences between modalities were, however, small and might not be clinically significant. As expected, margins that envelop the CTV motion provide dosimetric protection against motion for all three modalities.