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Gestational Radiation Effects (for radiologic technologists)

Gestational Radiation Effects are an important point for all radiologic technologists to understand. The radiation effects depend strongly on the gestational phase at which the radiation is dose is received. For illustrated reference guide see our post: https://howradiologyworks.com/fertili... In first phase, the pre-implantation stage, the embryo is formed and it is less than a few days old. The embryo has not yet been implanted into the uterus. As seen in this figure the pre-implantation stage is about one week. Chapters: 00:00. Intro 01:32. Stages of Gestation 03:05. Pre-implantation Radiation Risks 03:55. Organogenesis Radiation Risks 04:41. Fetal Stage Radiation Risks 05:37 Summary Gestational Radiation Risks 06:45. Diagnostic radiation doses The next phase in the gestational timeline is referred to as organogenesis where the undifferentiated cells from pre-implantation now start to become differentiated. The organ systems begin to be formed during this phase. In the organogenesis phase cells start to become differentiated and start to have a destiny as to which specific type of organ they will become. The third period, from approximately six weeks to the birth, is called the fetal period. After the organogenesis phase the organs are formed. During the fetal period there is significant development and growth. Risks from radiation exposure at different stages Pre-implantation stage In this phase an embryo has been formed but the cells are not yet differentiated, and therefore radiation damage cannot affect specific organs (as the cells are all the same, and not organ specific yet). When radiation exposure occurs, it will cause either death of the embryo or no damage at all. This is a very binary event with radically different outcomes. Therefore, in the pre-implantation stage there are no specific side effects that can be observed. Organogenesis Stage During this stage, organs are actively being developed and this phase is relatively radiosensitive. During organogenesis radiation exposure can cause birth abnormalities or even neonatal death. In animal experiments the relative likelihood of abnormalities increases with radiation dose, until the dose level at which there are abnormalities observed in 100% of the population. In experiments in mice this occurred with radiation doses of 2 Gy. Microcephaly or small head size and reduced growth have been observed among atomic bomb survivors who received the radiation during this critical gestational phase. Fetal Stage In this phase, organs are formed and the risk of abnormalities caused by radiation exposure are lower than during organogenesis. Experiments on mice showed that there are risks of permanents growth retardation from exposure during the fetal period. Growth retardation and higher risks of mental retardation have also been documented among atomic bomb survivors where the surviving baby was in the fetal phase during the radiation exposure. There is also an estimated cancer induction risk that is 6% higher per Gray of radiation exposure. Given all of these risks, after a pregnancy is declared, the radiation dose which is allowable is only 0.5 millisieverts (mSv) per month. Summary of Gestational Risks We would like to summarize once again the the different stages of gestation and the risks that have been identified in animal experiments and in atomic bomb survivors. In the pre-implantation stage, animal experiments showed that radiation doses might cause prenatal death. In atomic bomb survivors, it’s assumed that there was prenatal death because the individual never would have known that there was an embryo that had not yet implanted. During the organogenesis phase, animal experiments indicated increase rates of neonatal death and abnormalities. While the risks are lower during the fetal period there is still the of potential of growth and mental retardation. Context of Diagnostic Imaging There have been a number of thoughtful works presented by Cynthia McCollough’s CT group at Mayo on this topic. In this educational paper a good summary is provided in one of the references from the American College of Committee of Obstetricians and Gynecologists (Guidelines for diagnostic imaging during pregnancy. ACOG Committee opinion no. 299, September 2004): “Women should be counseled that the x-ray exposure from a single diagnostic procedure does not result in harmful fetal effects, specifically exposure to less than 5 rad or 50 milligray has not been associated with an increase in fetal abnormalities or pregnancy loss.” As with all diagnostic exams the doses should be kept as low as reasonably achievable and for certain clinical indications alternative diagnostic modalities may be considered such as ultrasound, but the value of the clinical information gained from x-ray or CT can be significant to confirm or rule out a given diagnosis.