Ionizing radiation during pregnancy can negatively impact a fetus. In light of the Fukushima nuclear plant disaster in Japan, we discuss existing knowledge on the health effects of radiation and preventive measures for pregnant women. Overall, the risk of exposure to radiation is limited but severe defects can result from fetal radiation exposure >100 mGy equivalent to 10 rad (>1000 chest x-rays). While such high-level exposure rarely occurs during single medical diagnostic procedures, caution should be exercised for pregnant women. As a protective public health measure in light of a disaster, evacuation, shielding, and elimination of ingested radioactive isotopes should all be considered. Detailed radiation reports with health effects and precautionary measures should be available for a population exposed to more than background radiation.
The disaster at the Fukushima Daiichi nuclear plants in Japan has led to renewed fear around the world of the negative health effects of ionizing radiation. Media reports of pregnant women fleeing Fukushima highlight the particularly disconcerting risk perceived for pregnant women and infants.
In times of nuclear disasters or radiation exposure it is crucial for medical professionals to be well informed and to understand the nature and characteristics of radiation and its potential hazardous effects on health and, especially, pregnancy. This article provides guidance to understand the types of radiation and units of dose measurements, health impact of high-dose radiation from disasters and on pregnancy and lactation, and measures that may be taken in the event of radiation exposure.
Radiation and measurement in dose units
Radiation, ie, any “energy that comes from a source and travels through some material or through space,” can be categorized as either ionizing or nonionizing. Nonionizing radiation “has enough energy to move around atoms in a molecule or cause them to vibrate, but not enough to remove electrons” ; examples include ultrasound waves, visible light, microwaves, and magnetic resonance imaging.
Ionizing radiation “has enough energy to remove tightly bound electrons from atoms, thus creating ions” and consists of either particulate or electromagnetic energy. Examples of particulate energy include alpha particles, which have a short travel range and cannot penetrate more than a single layer of skin, and beta particles, which have moderate penetrating power but can still only traverse a few millimeters of skin. While alpha and beta particles generally do not pose a significant health threat due to their lack of penetrating power, when inhaled, ingested, or injected, they may act as carcinogens or initiate other adverse health effects.
Electromagnetic energy includes gamma rays and x-rays, both of which can travel thousands of meters in air and penetrate many materials, including human tissues. As a result, exposure to these types of radiation can result in significant damage to organs.
The International System of Units (SI) has 4 unit measures ( Table 1 ). Generally, the dose equivalent, ie, sievert (Sv), is used to measure the public exposure to radiation as it accounts for factors such as the type of radiation, amount of time exposed, level of protection, and distance from the radiation source. In describing the potential radiation exposure from medical diagnostic equipment, gray (Gy) is the SI unit, but radiation absorbed dose (rad) is the predominant measure used. In this article, we adhere to the SI unit gray (Gy) or milligray (mGy) for readability and will provide the rad-converted amount in brackets for readers’ convenience.
| Variable | Commonly used units | SI units | Conversion |
|---|---|---|---|
| Radio activity a | Curie (Ci) | Becquerel (Bq) | 1 Ci relates to 37 gigabecquerel (GBq) |
| 1 Ci = 1g of radium | 1 Bq = 1 decay/s | 1 GBq relates to 27 mCi | |
| Exposure b | Roentgen (R) | Coulomb (C)/kg | 1 R relates to 258 μC/kg |
| 1 C/kg relates to 3876 R | |||
| Absorbed dose c | Radiation absorbed dose (rad) | Gray (Gy) | 1 Gy = 100 rad |
| 1 Gy = 1 J/kg | 1 rad = 0.1 Gy | ||
| Equivalent dose d | Roentgen equivalents man (rem) | Sievert (Sv) | 1 Sv = 100 rem |
| 1 Sv = 1 Gy × radiation weighting factor (Wr) | 1 rem = 0.1 Sv |
a Radio activity is measurement for source of radiation and depends on type and amount of material and distance from where measurement is taken. Conversion from curie to becquerel is not the same for every material, but this equation is commonly cited;
b Exposure is only used for gamma and x-ray. Alpha, beta, and neutrons cannot be calculated in roentgen. Measurement of exposure can be done by Geiger counters (or other survey meters) that will give information on radiation per time period in a certain location. Dosimeters will calculate accumulative dose of exposure over time;
c Absorbed dose is energy deposited by radiation (J)/kg. Since tissue differs in density, same amount of radiation will give a different absorbed dose to different tissue, calculated using tissue-weighting factor;
d Equivalent dose is dose calculated as if a body is homogeneously exposed to radiation, taking into account that tissues have different density and taking into account the impact factor of different radiation types. Impact factor is sometimes called radiation weighting factor (Wr). For x-ray, the gamma and beta radiation impact factor is 1 and therefore 1 Gy = 1 Sv. For alpha radiation, the impact factor is 20. Alpha radiation is more harmful for the human body. In medical practice, radiation exposure is mostly related to x-ray. Therefore, equation of 1 R = 1 rad = 1 rem is often accepted, although not totally reflecting reality.
When interpreting ionizing radiation exposure, “background” radiation should be considered. Ionizing radiation originates from space and natural resources, and exists everywhere including soil, water, and air. On average, a person is exposed to 2.4 mSv of background radiation every year. This background radiation translates into 1 mSv of background radiation for the fetus for a full-term pregnancy. The precise amount of background radiation exposure varies in different parts of the world, depending on the altitude and the quality of the atmosphere. Table 2 illustrates the estimated fetal radiation absorption dose for various events potentially experienced by pregnant women.
| Clinical suspicion | Procedure | Estimated fetal absorption (mGy) per procedure | Estimated fetal absorption (rad) per procedure |
|---|---|---|---|
| Pneumonia | X-ray chest | <0.01 | <0.001 |
| Pulmonary embolism | CT scan | 0.06-0.96 | 0.006-0.096 |
| VP scan | 0.1-0.37 | 0.01-0.037 | |
| Appendicitis | Ultrasound | Nonionizing radiation | Nonionizing radiation |
| CT scan abdomen | 8-49 | 0.8-0.49 | |
| MRI | Nonionizing radiation | Nonionizing radiation | |
| Nephrolithiasis | Ultrasound | Nonionizing radiation | Nonionizing radiation |
| X-ray abdomen | 1-4.2 | 0.1-0.42 | |
| Pyelogram | 1.7-10 | 0.17-1 | |
| CT scan abdomen | 8-49 | 0.8-4.9 | |
| MRI | Nonionizing radiation | Nonionizing radiation | |
| Breast nodule | Ultrasound | Nonionizing radiation | Nonionizing radiation |
| Mammogram | 0.07-0.2 | 0.007-0.02 | |
| Colon pathology | X-ray abdomen | 1-4.2 | 0.1-0.42 |
| Barium enema | 7 | 0.7 | |
| Trauma | |||
| Spine injury | X-ray lumbar spine | 6 | 0.6 |
| X-ray thoracic/cervical spine | <0.01 | <0.001 | |
| X-ray skull | <0.01 | <0.001 | |
| Pelvic injury | X-ray pelvis | 1.1-4 | 0.11-0.4 |
| CT scan pelvis | 20-79 | 2.0-7.9 | |
| Abdominal injury | Ultrasound (FAST) | Nonionizing radiation | Nonionizing radiation |
| CT scan abdomen | 8-49 | 0.8-4.9 | |
| MRI | Nonionizing radiation | Nonionizing radiation | |
| Background radiation | None | 1 mSv | 0.1 rem a |
| Commercial flight | Round trip Toronto-Frankfurt | 0.1 mSv | 0.01 rem a |
| 100 h of commercial flying | 1 mSv | 0.1 rem a |
a 1 rem is comparable but not equivalent to 1 rad; see Table 1 for further explanation.
Health impact of high-dose radiation from a nuclear disaster
The International Atomic Energy Agency developed the International Nuclear Events Scale to measure the health significance and environmental impact of all events associated with the transportation, storage, and use of radioactive materials ( Table 3 ). Using the International Nuclear Events Scale, radiation exposure events are classified on a scale ranging from 1–7. Both the Chernobyl and Fukushima disasters were classified as a 7, the highest possible rating.
| INES scale | Description | Implication |
|---|---|---|
| 1 | Anomaly | Unwanted exposure without noted harm; eg, lost or stolen radioactive transport package |
| 2 | Incident | Unwanted exposure >50 mSv/h or worker with nuclear material exceeding annual radiation exposure |
| 3 | Serious incident | Nonlethal unwanted radiation effects in population, eg, skin reddening or burns; exposure is >1 mSv/h |
| 4 | Accident with local consequences | 1 death due to radiation; no need for public health countermeasures |
| 5 | Accident with wider consequences | >1 death and need for limited countermeasures |
| 6 | Serious accident | More deaths and possibly need for extensive countermeasures |
| 7 | Major accident | Widespread radioactivity causing negative environmental and health effects including radiation deaths; extensive countermeasures are needed |
In a radiation disaster, the nature and intensity on health will depend on which areas of the body were exposed and what intake pathways were used for absorption. The most common health effect of high-dose radiation exposure is cell death; an effect that is positively used for cancer treatment. However, high-dose ionizing radiation can also alter the DNA of normal cells and cause uncontrolled cell divisions, thereby inducing cancer. In addition, uncontrolled and excessive exposure to high-dose radiation can damage organs and result in acute radiation sickness (including coagulopathy and immunity disorders), diarrhea, fever, burns, and coordination and equilibrium disturbances.
During the Chernobyl disaster, where the peak radioactivity reached 14 exabecquerel approximately 150 on-site emergency workers developed acute radiation sickness and 28 of them died as a result within a year. In addition to acute illness, many survivors of the initial exposure at Chernobyl, Nagasaki, and Hiroshima suffered long-term negative health consequences that included leukemia; thyroid, breast, and skin cancers; and cataracts.
When looking specifically at the effects of radiation on a fetus, it is important to first note that the radiation dose that a pregnant woman is exposed to or absorbs may not directly transfer to the fetus. A fetus is partly protected from radiation injury by a pregnant woman’s surrounding soft tissues and uterus, both of which generally stop alpha and beta particles from penetration if they are not ingested, injected, or inhaled; however, gamma and x-rays directed toward the abdomen of a pregnant woman who is not appropriately shielded can reach and harm a fetus. Of note is that the placenta can transfer radioactive ions ingested, injected, or inhaled by a pregnant woman and radioactive material that accumulates in the bladder of a pregnant woman may cause internal radiation exposure to the nearby fetus.
Health impact of high-dose radiation from a nuclear disaster
The International Atomic Energy Agency developed the International Nuclear Events Scale to measure the health significance and environmental impact of all events associated with the transportation, storage, and use of radioactive materials ( Table 3 ). Using the International Nuclear Events Scale, radiation exposure events are classified on a scale ranging from 1–7. Both the Chernobyl and Fukushima disasters were classified as a 7, the highest possible rating.
| INES scale | Description | Implication |
|---|---|---|
| 1 | Anomaly | Unwanted exposure without noted harm; eg, lost or stolen radioactive transport package |
| 2 | Incident | Unwanted exposure >50 mSv/h or worker with nuclear material exceeding annual radiation exposure |
| 3 | Serious incident | Nonlethal unwanted radiation effects in population, eg, skin reddening or burns; exposure is >1 mSv/h |
| 4 | Accident with local consequences | 1 death due to radiation; no need for public health countermeasures |
| 5 | Accident with wider consequences | >1 death and need for limited countermeasures |
| 6 | Serious accident | More deaths and possibly need for extensive countermeasures |
| 7 | Major accident | Widespread radioactivity causing negative environmental and health effects including radiation deaths; extensive countermeasures are needed |
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