Bednarz Bryan, Xu X George
Nuclear Engineering and Engineering Physics Program, Rensselaer Polytechnic Institute, Troy, New York 12180, USA.
Med Phys. 2008 Jul;35(7):3054-61. doi: 10.1118/1.2938519.
A Monte Carlo-based procedure to assess fetal doses from 6-MV external photon beam radiation treatments has been developed to improve upon existing techniques that are based on AAPM Task Group Report 36 published in 1995 [M. Stovall et al., Med. Phys. 22, 63-82 (1995)]. Anatomically realistic models of the pregnant patient representing 3-, 6-, and 9-month gestational stages were implemented into the MCNPX code together with a detailed accelerator model that is capable of simulating scattered and leakage radiation from the accelerator head. Absorbed doses to the fetus were calculated for six different treatment plans for sites above the fetus and one treatment plan for fibrosarcoma in the knee. For treatment plans above the fetus, the fetal doses tended to increase with increasing stage of gestation. This was due to the decrease in distance between the fetal body and field edge with increasing stage of gestation. For the treatment field below the fetus, the absorbed doses tended to decrease with increasing gestational stage of the pregnant patient, due to the increasing size of the fetus and relative constant distance between the field edge and fetal body for each stage. The absorbed doses to the fetus for all treatment plans ranged from a maximum of 30.9 cGy to the 9-month fetus to 1.53 cGy to the 3-month fetus. The study demonstrates the feasibility to accurately determine the absorbed organ doses in the mother and fetus as part of the treatment planning and eventually in risk management.
已开发出一种基于蒙特卡罗方法的程序，用于评估6兆伏外部光子束放射治疗对胎儿的剂量，以改进基于1995年发布的美国医学物理师协会任务组报告36的现有技术[M. 斯托瓦尔等人，《医学物理》22, 63 - 82 (1995)]。将代表妊娠3个月、6个月和9个月阶段的孕妇解剖学逼真模型与能够模拟加速器头部散射和泄漏辐射的详细加速器模型一起植入MCNPX代码中。针对胎儿上方部位的六种不同治疗计划以及膝部纤维肉瘤的一种治疗计划，计算了胎儿的吸收剂量。对于胎儿上方的治疗计划，胎儿剂量往往随着妊娠阶段的增加而增加。这是由于随着妊娠阶段的增加，胎儿身体与射野边缘之间的距离减小。对于胎儿下方的治疗野，由于胎儿尺寸增大以及每个阶段射野边缘与胎儿身体之间的距离相对恒定，吸收剂量往往随着孕妇妊娠阶段的增加而降低。所有治疗计划中胎儿的吸收剂量范围从9个月胎儿的最高30.9厘戈瑞到3个月胎儿的1.53厘戈瑞。该研究证明了在治疗计划中以及最终在风险管理中准确确定母亲和胎儿吸收器官剂量的可行性。
