Nuclear Engineering and Engineering Physics Program, Rensselaer Polytechnic Institute, Troy, NY 12180, USA.
Phys Med Biol. 2012 May 7;57(9):2441-59. doi: 10.1088/0031-9155/57/9/2441. Epub 2012 Apr 5.
Although it is known that obesity has a profound effect on x-ray computed tomography (CT) image quality and patient organ dose, quantitative data describing this relationship are not currently available. This study examines the effect of obesity on the calculated radiation dose to organs and tissues from CT using newly developed phantoms representing overweight and obese patients. These phantoms were derived from the previously developed RPI-adult male and female computational phantoms. The result was a set of ten phantoms (five males, five females) with body mass indexes ranging from 23.5 (normal body weight) to 46.4 kg m(-2) (morbidly obese). The phantoms were modeled using triangular mesh geometry and include specified amounts of the subcutaneous adipose tissue and visceral adipose tissue. The mesh-based phantoms were then voxelized and defined in the Monte Carlo N-Particle Extended code to calculate organ doses from CT imaging. Chest-abdomen-pelvis scanning protocols for a GE LightSpeed 16 scanner operating at 120 and 140 kVp were considered. It was found that for the same scanner operating parameters, radiation doses to organs deep in the abdomen (e.g., colon) can be up to 59% smaller for obese individuals compared to those of normal body weight. This effect was found to be less significant for shallow organs. On the other hand, increasing the tube potential from 120 to 140 kVp for the same obese individual resulted in increased organ doses by as much as 56% for organs within the scan field (e.g., stomach) and 62% for those out of the scan field (e.g., thyroid), respectively. As higher tube currents are often used for larger patients to maintain image quality, it was of interest to quantify the associated effective dose. It was found from this study that when the mAs was doubled for the obese level-I, obese level-II and morbidly-obese phantoms, the effective dose relative to that of the normal weight phantom increased by 57%, 42% and 23%, respectively. This set of new obese phantoms can be used in the future to study the optimization of image quality and radiation dose for patients of different weight classifications. Our ultimate goal is to compile all the data derived from these phantoms into a comprehensive dosimetry database defined in the VirtualDose software.
虽然人们已经知道肥胖会对 X 射线计算机断层扫描（CT）图像质量和患者器官剂量产生深远影响，但目前还没有描述这种关系的定量数据。本研究使用新开发的代表超重和肥胖患者的体模，检查肥胖对 CT 计算器官和组织辐射剂量的影响。这些体模是由先前开发的 RPI-成人男性和女性计算体模衍生而来的。结果是一组十个体模（五个男性，五个女性），体重指数范围从 23.5（正常体重）到 46.4 kg m(-2)（病态肥胖）。体模使用三角网格几何形状建模，并包含指定量的皮下脂肪组织和内脏脂肪组织。基于网格的体模然后被体素化，并在蒙特卡罗 N-粒子扩展代码中定义，以计算 CT 成像的器官剂量。考虑了用于通用电气 LightSpeed 16 扫描仪在 120 和 140 kVp 操作的胸部-腹部-骨盆扫描方案。结果发现，对于相同的扫描仪操作参数，与正常体重的人相比，肥胖个体的腹部深处（例如结肠）器官的辐射剂量可以小 59%。对于浅层器官，这种影响不太明显。另一方面，对于同一肥胖个体，将管电压从 120 增加到 140 kVp，会导致扫描场（例如胃）内器官的器官剂量增加高达 56%，扫描场外（例如甲状腺）的器官剂量增加 62%。由于通常为较大的患者使用更高的管电流以保持图像质量，因此量化相关的有效剂量很重要。本研究发现，当肥胖水平-I、肥胖水平-II 和病态肥胖体模的 mAs 增加一倍时，与正常体重体模相比，有效剂量分别增加 57%、42%和 23%。这组新的肥胖体模将来可用于研究不同体重分类患者的图像质量和辐射剂量优化。我们的最终目标是将这些体模中得出的所有数据编译到 VirtualDose 软件中定义的综合剂量学数据库中。
