Department of Medical Physics, University of Crete, Iraklion, Greece.
Phys Med. 2011 Oct;27(4):181-7. doi: 10.1016/j.ejmp.2010.12.004. Epub 2011 Jan 8.
This study aimed to estimate fetal dose from mantle field irradiation with 6 MV photons and to determine the proper fetal shielding conditions. The Monte Carlo N-particle code and mathematical phantoms representing pregnancy at the first, second and third trimesters of gestation were used to calculate fetal dose with or without the presence of a 5-cm-thick lead shield of dimensions 35×35 cm(2). Fetal exposure was calculated for lead thicknesses of 2, 3, 4, 6, 7 and 8 cm. The dependence of fetal dose upon the distance separating the shield from the beam edge and phantom's abdomen was investigated. Dose measurements were performed on a physical phantom using thermoluminescent dosimetry. The radiation dose to an unshielded and shielded fetus was 0.578-0.861% and 0.180-0.641% of the prescribed tumor dose, respectively, depending upon the gestational age. The lead thickness increase from 2 to 5 cm led to a fetal dose reduction up to 23.4%. The use of 5- to 8-cm-thick lead resulted in dose values differing less than 4.5%. The shift of the lead from the closer to the more distant position relative to the field edge increased fetal dose up to 42.5%. The respective increase by changing the distance from the phantom's abdomen was 21.9%. The difference between dose calculations and measurements at specific points was 8.3±3.9%. The presented data may be used for fetal dose assessment with different shielding settings before treatment and, then, for the design and construction of the appropriate shielding device.
本研究旨在估算 6MV 光子全斗篷野照射的胎儿剂量，并确定适当的胎儿屏蔽条件。使用蒙特卡罗 N 粒子代码和代表妊娠头三个月、第二个三个月和第三个三个月的数学体模来计算有或没有 35×35cm2、5cm 厚的铅屏蔽的情况下的胎儿剂量。计算了厚度为 2、3、4、6、7 和 8cm 的铅的胎儿暴露。研究了屏蔽与束边缘和体模腹部之间的距离对胎儿剂量的影响。使用热释光剂量计在物理体模上进行剂量测量。未屏蔽和屏蔽胎儿的辐射剂量分别为 0.578-0.861%和 0.180-0.641%的处方肿瘤剂量，这取决于妊娠年龄。铅厚度从 2cm 增加到 5cm 导致胎儿剂量减少了 23.4%。使用 5-8cm 厚的铅会导致剂量值差异小于 4.5%。相对于场边缘，将铅从更近的位置移到更远的位置会增加胎儿剂量，最高可达 42.5%。通过改变与体模腹部的距离，相应的增加为 21.9%。在特定点的剂量计算和测量之间的差异为 8.3±3.9%。所提供的数据可用于治疗前评估不同屏蔽设置下的胎儿剂量，然后用于设计和构建适当的屏蔽装置。
