Mountford P J, Steele H R
Department of Nuclear Medicine, Queen Elizabeth Hospital, Edgbaston, Birmingham, UK.
Eur J Nucl Med. 1995 Oct;22(10):1173-9. doi: 10.1007/BF00800600.
The International Commission on Radiological Protection has recently recommended a supplementary dose limit of 2 mSv to the abdominal surface of a pregnant member of staff in order to provide protection to her fetus comparable to that in members of the public, whose annual limit is recommended to be 1 mSv. In order to determine whether this apparent attenuation factor of 50% is appropriate for nursing and imaging staff exposed to nuclear medicine patients, estimates were made of the ratios of the maternal abdominal surface to fetal dose appropriately weighted for time, distance and dose rate. Thermoluminescent dosimeter (TLD) measurements were made at various depths in an anthropomorphic phantom irradiated at different distances by a distributed source of either technetium-99m or iodine-131 in order to determine the corresponding attenuation factors at the average fetal midline depth. Dose estimates were based on these factors and on published values of dose rate and exposure times for nursing and imaging staff at these distances from the patient. Fetal doses to nursing staff caring for an adult 99mTc patient were estimated to vary from 86 microSv to 1.6 microSv, with the corresponding ratio of the abdominal surface to fetal dose varying from about 1.8:1 to 1.5:1 as the patient became less dependent on nursing care and the mean distance from the patient increased. Fetal doses to imaging staff varied from 1.12 microSv to 0.17 microSv for three types of 99mTc scan, but the ratio only varied from 1.4:1 to 1.3:1. Fetal doses to imaging staff were estimated to be 6.7 microSv and 9.0 microSv for a whole-body scan of a thyroid cancer patient after 131I ablation and therapy respectively, and the ratio was 1.3:1 for both types of scan. It was concluded that for a pregnant ward nurse or imaging technologist exposed to an adult or paediatric patient administered 99mTc or 131I, a dose limit of 1.3 mSv to the maternal abdominal surface will restrict their fetal dose to 1 mSv. A pregnant imaging technologist should perform no more than six adult 99mTc studies or one 131I whole-body scan per day, and may have to wear a more sensitive personal dosimeter than a film badge.
国际放射防护委员会最近建议对怀孕工作人员的腹部表面设定2毫希沃特的补充剂量限值，以便为其胎儿提供与公众成员相当的保护，公众的年剂量限值建议为1毫希沃特。为了确定这一明显的50%衰减系数是否适用于接触核医学患者的护理和影像工作人员，对母体腹部表面剂量与胎儿剂量之比进行了估算，并根据时间、距离和剂量率进行了适当加权。在一个人体模型的不同深度进行了热释光剂量计（TLD）测量，该人体模型由锝-99m或碘-131的分布式源在不同距离进行照射，以确定胎儿平均中线深度处的相应衰减系数。剂量估算基于这些系数以及已公布的护理和影像工作人员在这些距离处与患者的剂量率和照射时间值。照顾成年99mTc患者的护理人员的胎儿剂量估计在86微希沃特至1.6微希沃特之间，随着患者对护理的依赖减少且与患者的平均距离增加，母体腹部表面剂量与胎儿剂量的相应比值从约1.8:1变化至1.5:1。对于三种类型的99mTc扫描，影像工作人员的胎儿剂量在1.12微希沃特至0.17微希沃特之间，但比值仅从1.4:1变化至1.3:1。对于接受131I消融和治疗后的甲状腺癌患者进行全身扫描，影像工作人员的胎儿剂量估计分别为6.7微希沃特和9.0微希沃特，两种扫描类型的比值均为1.3:1。得出的结论是，对于接触接受99mTc或131I治疗的成年或儿科患者的怀孕病房护士或影像技师，母体腹部表面剂量限值为1.3毫希沃特将把他们胎儿的剂量限制在1毫希沃特。怀孕的影像技师每天进行的成年99mTc检查不应超过六项或一次131I全身扫描，并且可能需要佩戴比胶片徽章更灵敏的个人剂量计。
