Rankine Ashley W, Lanzon Peter J, Spry Nigel A
Department of Radiation Oncology, Sir Charles Gairdner Hospital, Verdun Street, Nedlands, Perth, WA 6009, Australia.
Med Dosim. 2008 Autumn;33(3):169-74. doi: 10.1016/j.meddos.2007.04.007.
The purpose of this study was to quantify changes in photon beam dosimetry caused by using contrast media during computed tomography (CT) simulation and determine if the resulting changes are clinically significant. The effect of contrast on dosimetry was first examined for a single 6-MV photon beam incident on a plane phantom with a structure of varying electron densities (rho(e)) and thickness. Patient studies were then undertaken in which CT data sets were collected with and without contrast for 6 typical patients. Three patients received IV contrast (Optiray-240) only and 3 received IV plus oral (Gastrograffin) contrast. Each patient was planned using conformal multifield techniques in accordance with the department standards. Two methods were used to compare the effect of contrast on dosimetry for each patient. The phantom analysis showed that the change in dose at the isocenter for a single 10 x 10 cm2 6-MV photon beam traversing 10 cm of a contrast-enhanced structure with rho(e) 1.22 was 7.0% (1.22 was the highest average rho(e) observed in the patient data). As a result of using contrast, increases in rho(e) were observed in structures for the 6 patients studied. Consequently, when using contrast-enhanced CT data for multifield planning, increases in dose at the isocenter and in critical structures were observed up to 2.1% and 2.5%, respectively. Planning on contrast-enhanced CT images may result in an increase in dose of up to 2.1% at the isocenter, which would generally be regarded as clinically insignificant. If, however, a critical organ is in close proximity to the planning target volume (PTV) and is planned to receive its maximum allowable dose, planning on contrast-enhanced CT images may result in that organ receiving dose beyond the recommended tolerance. In these instances, pre-contrast CT data should be used for dosimetry.
本研究的目的是量化在计算机断层扫描（CT）模拟过程中使用造影剂引起的光子束剂量测定的变化，并确定由此产生的变化是否具有临床意义。首先，研究了一束6兆伏光子束入射到具有不同电子密度（ρ(e)）和厚度结构的平面体模上时，造影剂对剂量测定的影响。然后进行了患者研究，收集了6例典型患者在使用和不使用造影剂情况下的CT数据集。3例患者仅接受静脉造影剂（碘海醇-240），3例患者接受静脉加口服（泛影葡胺）造影剂。每位患者均按照科室标准采用适形多野技术进行计划。使用两种方法比较每位患者造影剂对剂量测定的影响。体模分析表明，一束10×10平方厘米的6兆伏光子束穿过10厘米ρ(e)为1.22的造影增强结构时，等中心处的剂量变化为7.0%（1.22是在患者数据中观察到的最高平均ρ(e)）。在所研究的6例患者中，使用造影剂后，各结构的ρ(e)均有所增加。因此，在使用造影增强CT数据进行多野计划时，等中心处和关键结构的剂量分别增加了高达2.1%和2.5%。基于造影增强CT图像进行计划可能会导致等中心处的剂量增加高达2.1%，一般认为这在临床上无显著意义。然而，如果关键器官紧邻计划靶体积（PTV），且计划接受其最大允许剂量，基于造影增强CT图像进行计划可能会导致该器官接受的剂量超过推荐的耐受剂量。在这些情况下，应使用造影前CT数据进行剂量测定。
