Ionizing Radiation
At a Glance
Ionizing radiation is any form of radiation with enough energy to alter an atom, such as X-rays or nuclear energy. Evidence from studies of medical exposures to radiation as well as large-scale disasters such as exposures from the atomic bomb in Japan has demonstrated that radiation can cause breast cancer.
The International Agency for Research on Cancer (IARC) and the National Toxicology Program (NTP) classify it as a known human carcinogen.
What is ionizing radiation?
Ionizing radiation is any form of radiation with enough energy to break off electrons from atoms (meaning to ionize the atoms). This radiation can break the chemical bonds in molecules, including DNA molecules, thereby disturbing their normal functioning. X-rays and gamma rays are the only major forms of radiation with sufficient energy to penetrate and damage body tissue below the surface of the skin.
Where is ionizing radiation found?
Ionizing radiation exposures occur in a variety of medical and occupational settings as well as from disasters such as the dropping of the atomic bomb in Japan.
- Medical radiological procedures:
- X-rays
- Computed tomography (CT) scans
- Fluoroscopy, a medical diagnostic test that shows moving parts, often used in cardiovascular procedures
- Sources of gamma ray emissions:
- Nuclear power plants
- Radionucleotide research
- Military weapons testing
- Nuclear medicine procedures such as bone, thyroid and lung scans
- Prior to 2013, backscatter X-ray screening machines led to exposures in airports.
What evidence links ionizing radiation to breast cancer?
Exposure to ionizing radiation is the best-established and longest-established environmental cause of human breast cancer in both men and women. Most scientists agree that no safe dose of radiation has been identified.[1],[2] Repeated low-dose exposures over time may have the same harmful effects as a single high-dose exposure.
- The link between radiation exposure and breast cancer has been demonstrated in survivors of the atomic bombing in Japan, particularly among women who were younger than 20 when the bombs were dropped.[3],[4],[5],[6], The effect of radiation exposure was especially strong for women whose age of menarche was 12 or younger and who were exposed by age 20.[7]
- Ionizing radiation can increase the risk for breast cancer by a number of different mechanisms, including direct mutagenesis, genome instability[8],[9] and changes in breast cell micro-environments that can lead to damaged regulation of cell-cell interactions within the breast.[10],[11],[12]
- Ionizing radiation not only affects cells that are directly exposed, but can alter the DNA, cell growth and cell-cell interactions of neighboring cells, a phenomenon referred to as the “bystander effect.”[13]
- While exposures to ionizing radiation from radon gas are not associated with and overall increased risk for breast cancer, there is a specific association of exposure to radon and increased risk for PR-/ER- breast cancers.
- Ionizing radiation not only affects cells that are directly exposed, but can alter the DNA, cell growth and cell-cell interactions of neighboring cells, a phenomenon referred to as the “bystander effect.”[14],[15]
Occupational exposures
- Studies show increased risk of breast cancer among radiological technologists who began working during their teens or were working in the field before the 1940s.[16], [17]
- It was also found that technologists who began working before 1950 and had worked for at least five years had an increased mortality rate from breast cancer.[18] Levels of exposure before 1950 were much higher than those found for technologists today.
- A review and analysis of all existing related studies found that women who work as airline flight attendants were exposed to higher cosmic radiation while flying and also had increased levels of breast cancer.[19]
Medical radiation
Although there has been a substantial decrease in exposures to ionizing radiation from individual X-rays over the past several decades, there has been a six-fold increase in overall exposure to medical sources of radiation.[20],[21] A recent estimate of all cancers attributable to medical radiation exposures in France found that the largest number was for breast cancer.[22]
- X-rays: Decades of research have confirmed the link between radiation and breast cancer in women who were irradiated for many different medical conditions, from tuberculosis[23] to benign breast disease[24],[25] and even acne.[26] Evidence from almost all conditions suggests that exposure to ionizing radiation during childhood and adolescence is particularly dangerous with respect to increased risk for breast cancer later in life,[27],[28],[29] and that there is a significant dose-response relationship between the dosage of childhood radiation and the increased incidence of breast cancer.[30]
- Computed tomography (CT) Scans: When a CT scan is directed at the chest, the individual receives radiation equivalent to 30 to 442 chest X-rays.[31] Other modeling suggests that 1 in 150 women who are 20 years old when they undergo CT angiograms of the chest, and 1 in 270 women of all ages having the procedure, will subsequently develop cancers of the chest, including breast cancer.[32]
- Mammography: Recent evidence indicates that the lower-energy X-rays provided by mammography resulted in substantially greater damage to DNA than would be predicted, and the effects of these exposures may be greatly underestimated when it comes to the risk of breast cancer.[33] For example, women who had multiple mammograms more than five years prior to diagnosis and started before age 35 had an increased risk of breast cancer.[34] Diagnostic radiation has been shown to increase risk for developing breast cancer in a dose-dependent manner for women who are BRCA positive and therefore more sensitive to radiation.[35]
- Radiation therapy: Researchers discovered a 16-fold increased relative risk of angiosarcoma (cancer of a blood vessel) in the breast and chest wall following irradiation of a primary breast cancer.[36] More recent data indicate that women younger than 45 who received the higher radiation exposure associated with post-lumpectomy radiotherapy had about a twofold increase in later contralateral breast cancer diagnoses. This effect was especially prominent in younger women with a significant family history of breast cancer.[37],[38],[39]
- Male breast cancer: Male breast cancer is relatively rare, but multiple exposures of men to medical radiation when they were young leads to a significant increase in risk for developing breast cancer several decades later.[40]
Backscatter security scanners
- Backscatter machines were put in place prior to a 2012 study that estimated that for every 2 million young girls who traveled by airplane once a week, one would develop breast cancer as a result.[41] In 2013, backscatter machines were removed from airports due to privacy concerns (not health concerns). Most airports now use millimeter wave screening, which does not use ionizing radiation.
Who is most likely to be affected by ionizing radiation?
Several factors interact with radiation to increase the potency of its carcinogenic effects:
- Age at exposure, genetic profile, and possibly estrogen levels.
- Direct exposure to radiation through military work or other occupations (listed above).
- Accidental or medical exposure to radiation more seriously affects children and adolescents than adults, with a greater chance of increasing their risk for breast cancer later in life.[42]
- CT angiography has been shown to cause a significant increase in risk of developing breast cancer, especially in pre-menopausal women.[43],[44]
- The effects of radiation on mammary carcinogenesis may be additive with effects of estrogens, as suggested by studies using human breast tumor cells in animals.[45],[46],[47] This is highly concerning due to the exposure levels of estrogen-mimicking chemicals in our environment.
Who is most vulnerable to the health effects of ionizing radiation?
- Everyone should be aware of the potential health hazards of ionizing radiation, but some women are more vulnerable than others to its health effects. Women carrying the BRCA1 mutation have deficits in many cell processes and a heightened sensitivity to the effects of radiation exposures.[48] These women are more likely to develop breast cancer and may be especially susceptible to the cancer-inducing effects of exposure to ionizing.[49],[50],[52],[51] This is especially true if women began exposures, including from mammography, at age 30 or earlier.[53]
- The detrimental risks from mammography might also be heightened in older women, whose breast epithelial cells have gone through several decades of cell division. Cells derived from older women’s breast tissue were more sensitive to the DNA-damaging effects of low-energy radiation, increasing the likelihood of later conversion to cancerous cells.[54]
- However, a recent laboratory study in rats indicates that having given birth and lactating the young was protective against development of breast cancers—especially ER+/PR+ tumors–in animals that had been exposed to radiation before puberty. This protective effect was not found if the animals had been exposed to the radiation as young adults.[55]
What are the top tips to avoid exposure?
- Discuss with your medical care team whether or not X-rays or CT scans are necessary and whether there are radiation-free alternatives. If you decide to seek out a second opinion, request that the original screening information be shared, to minimize the need for a second set of exposures if they are not necessary.
- Workers should follow recommended health and safety guidelines when working with any type of radiation, whether administering the radiation or taking part in a procedure where radiation is used.
- The U.S. Preventive Services Task Force recently recommended against the use of routine mammography screening before the age of 50 [56],[57] but supported the use of biennial screening between the ages of 50 and 75. Discuss with your doctor when you should begin regular mammograms, and how often they should be done, based on your individual family history and risk for breast cancer.
Updated 2019
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