Burridge Nichola A, Rowbottom Carl G, Burt Paul A
North Western Medical Physics, Christie Hospital NHS Trust, Manchester, United Kingdom.
J Appl Clin Med Phys. 2006 Nov 28;7(4):1-12. doi: 10.1120/jacmp.v7i4.2240.
The aim of this study was to investigate and, if possible, compensate for the effect of intravenous contrast-enhanced CT scans on the treatment planning dose distributions for lung patients. The contrast and noncontrast CT scans of 3 patients were registered, and the effect of contrast on the Hounsfield units (HU) was assessed. The effect of contrast was then simulated in the CT scans of 18 patients receiving radiotherapy of the lung by modification of the CT numbers for relevant sections of noncontrast-enhanced CT scans. All treatment planning was performed on the Pinnacle3 planning system. The dose distributions computed from simulated contrast CT scans were compared to the original dose distributions by comparison of the monitor units (MUs) for each beam in the treatment plan required to deliver the prescribed dose to the isocenter as well as a comparison of the total MUs for each patient, a percentage change in required MUs being equivalent to a percentage change in the dose. A correction strategy to enable the use of contrast-enhanced CT scans in treatment planning was developed, and the feasibility of applying the strategy was investigated by calculating dose distributions for both the original and simulated contrast CT scans. A mean increase in the overall patient MUs of 1.0 +/- 0.8% was found, with a maximum increase of 3.3% when contrast was simulated on the original CT scans. The simulated contrast scans confirmed that the use of contrast-enhanced CT scans for routine treatment planning would result in a systematic change in the dose delivered to the isocenter. The devised correction strategy had no clinically relevant effect on the dose distribution for the original CT scans. The application of the correction strategy to the simulated contrast CT scans led to a reduction of the mean difference in the overall MUs to 0.1 +/- 0.2% compared to the original scan, demonstrating that the effect of contrast was eliminated with the correction strategy. This work has highlighted the problems associated with using contrast-enhanced CT scans in heterogeneity corrected dose computation. Contrast visible in the CT scan is transient and should not be accounted for in the treatment plan. A correction strategy has been developed that minimizes the effect of intravenous contrast while having no clinical effect on noncontrast CT scans. The correction strategy allows the use of contrast without detriment to the treatment plan.
本研究的目的是调查并在可能的情况下补偿静脉注射对比增强CT扫描对肺癌患者治疗计划剂量分布的影响。对3例患者的增强CT扫描和非增强CT扫描进行配准，并评估对比剂对亨氏单位（HU）的影响。然后通过修改非增强CT扫描相关部位的CT值，在18例接受肺部放疗的患者的CT扫描中模拟对比剂的影响。所有治疗计划均在Pinnacle3计划系统上进行。通过比较治疗计划中每个射束将规定剂量输送至等中心所需的监测单位（MU），以及比较每个患者的总MU，将模拟对比增强CT扫描计算得到的剂量分布与原始剂量分布进行比较，所需MU的百分比变化等同于剂量的百分比变化。制定了一种在治疗计划中使用对比增强CT扫描的校正策略，并通过计算原始和模拟对比增强CT扫描的剂量分布来研究应用该策略的可行性。结果发现患者总体MU平均增加了1.0±0.8%，在原始CT扫描上模拟对比剂时最大增加了3.3%。模拟对比增强扫描证实，在常规治疗计划中使用对比增强CT扫描会导致输送至等中心的剂量发生系统性变化。所设计的校正策略对原始CT扫描的剂量分布没有临床相关影响。将校正策略应用于模拟对比增强CT扫描后，与原始扫描相比，总体MU的平均差异降低至0.1±0.2%，表明校正策略消除了对比剂的影响。这项工作突出了在异质性校正剂量计算中使用对比增强CT扫描所存在的问题。CT扫描中可见的对比剂是短暂的，不应在治疗计划中予以考虑。已制定了一种校正策略，可将静脉注射对比剂的影响降至最低，同时对非增强CT扫描没有临床影响。该校正策略允许使用对比剂而不损害治疗计划。
