Radiation exposure from medical imaging has received significant attention in the media, and many parents have questions about the potential harm from radiation and the best choice of imaging test for diagnosis. The following is a primer that offers the most likely 10 questions that pediatricians might be asked.
What Is Medical Radiation?
Medical ionizing radiation is made by high energy waves or particles that create ionized atoms that can be used for imaging, including image guidance, or for therapy, or for cancer therapy. Common imaging examinations that depend on medical radiation are radiographs (X-rays), fluoroscopic procedures, CT, and nuclear medicine examinations. Ultrasound and magnetic resonance imaging (MRI) use radiation, but not the higher energy found in ionizing radiation.
What Are the Risks from Medical Radiation?
Although it is difficult to prove that low level radiation such as that from diagnostic imaging examinations causes cancer, there are studies of large populations exposed to radiation that have concluded that there is a slight increase in cancer risk.1–11 Although the risk is uncertain and debated, this potential is of particular concern in children whose organs and tissues are more radiosensitive at younger ages, whose organs receive a larger dose for a given level of external radiation exposure than an adult would, and who have a longer lifetime to develop potential cancers as a result of medical radiation exposure.12 The potential risk is also considered additive with repeated radiation exposure.
How Does Medical Radiation Exposure Compare with Background Radiation?
Naturally occurring sources of ionizing radiation, also called background radiation, include cosmic rays and radon, and can also be found in certain foods (such as bananas and brazil nuts).13 People living at high elevations are routinely exposed to higher amounts of radiation than those living near sea level. As shown in Figure 1, the radiation used in X-rays and CT can be compared to the amount of background radiation a person gets in 1 year.
A pictorial guide for parents comparing the average amount of radiation used in pediatric X-rays and computed tomography to the amount of background radiation a person in the United States typically receives in 1 year. A millisievert (mSv) is a unit measurement of ionizing radiation dose.
How Much Radiation Is Used in the Different Imaging Modalities?
The annual average background radiation in the US is approximately 3 mSv.
For conventional X-rays (such as those of the extremities, chest, or abdomen/pelvis), the amount of radiation used is much less than the national annual average background radiation. A single chest X-ray is about the same amount as 4 days of average background exposure.
For other medical imaging studies, such as head CT, simple fluoroscopy procedures, and some nuclear medicine procedures (such as lung, kidney, liver, and bone scans), the amount of radiation is higher.
For some others, such as CT scans of the chest, abdomen, and pelvis, interventional (catheter-based) angiography, positron emission tomography/CT, and some nuclear medicine procedures (such as heart perfusion scans), the amount of radiation is relatively greater. However, with imaging tests such as CT, there are techniques that can be used to reduce radiation doses determined by the age and size of the child.
For X-rays and CT scans, radiation is only emitted during the study, unlike for nuclear medicine studies where the small amount of radiation is emitted from within the body, most often after intravenous administration. Figure 2 summarizes the relative radiation dose to children from common medical imaging examinations. Figure 3 explains the differences between CT and MRI, what the child can expect for each, and the best choice of imaging modality for common diagnoses.14
Relative radiation dose to children from common imaging examinations. Left to right on each gradient triangle for a given imaging study of a specific body part depicts lower to higher radiation dose. CT, computed tomography.
Comparison of computed tomography and magnetic resonance imaging—how images are created, what parents can expect, average scan duration, and common diagnoses best evaluated on each.
Which Radiology Examinations Contribute Most to Individual Patient Dose and Collective Population Dose in Children?
CT and interventional radiology procedures result in higher individual patient doses than other imaging studies.15 The patient dose from a CT examination is especially relevant in children when the exposure factors used for scanning children are the same as those used in adults.16 CT examinations are the largest contributor to collective population dose with head and abdominopelvic CTs constituting a large percentage of the total number of pediatric CT examinations.17
Do Radiation Doses Add Up Over Time?
This is a common and simple perspective, although there is support that the cumulative risk is less than the sum of the individual risks. For example, an examination with a dose of 10 mSv may carry a higher potential risk than 10 examinations, each with 1 mSv delivered once a month for 10 months. The most conservative position is to assume that the individual dose (and potential risks) from medical radiation exposure from all sources are each fully additive over a lifetime.
How Long Is There a Concern for Cancer Risk?
The potential risk for cancer from medical imaging can last for years, even decades. However, the risk for radiation-induced cancers should be evaluated against the statistical risk of developing cancer in the entire population. For any one person, the lifetime risk of death from cancer is about 1 in 518. Although estimates vary, the potential risk from medical imaging for a child may increase minimally or even not at all.3
How Can We Minimize Radiation Levels in Children?
It is important to have the child's imaging performed at a child-focused facility if possible. Although many clinics and hospitals offer diagnostic radiology, these may not all be set up toward optimization of child-based imaging techniques. The child's imaging studies performed at a pediatric-focused facility are more likely to use levels of radiation administered that are appropriate for the diagnostic question, especially for the wide range of sizes in children.
There are different approaches to avoid unnecessarily high (or too low) radiation to children during a CT imaging study. These include imaging only when there is a likely medical benefit; adjusting the dose to the size of the child; imaging only the indicated area; and minimizing the percentage of multiple passes or “series“ (different phases such as with intravenous iodine contrast administration) during the scan.
Are There Special Technical Methods to Reduce Patient Radiation Exposure While Still Maintaining Good Quality Diagnostic Images?
In pediatric-focused facilities and practices, pediatric protocols are routinely available to use the correct amount of radiation for the child, as opposed to using higher dose adult protocols. For procedures requiring fluoroscopy, special techniques are employed to lower the amount of radiation needed to produce high-quality imaging studies, including limiting the size of the radiation beam and using pulsed fluoroscopy (very few images [2–4] per second), which lessens the exposure.
Newer CT scanners have built-in dose-saving features designed to provide lower dose while preserving image quality. In addition, a further reduction in dose can be employed for certain indications, such as in CT head for shunt evaluation, CT for sinus evaluation, and CT for renal stones, among others.
Why Is Shielding No Longer Used?
As endorsed by several groups, including the American College of Radiology, the American Association of Physicists in Medicine, and the Image Gently Alliance ( www.imagegently.org), which all promote safe pediatric imaging, routine gonadal shielding during abdomen and pelvis Xrays (or during evaluation of more remote parts of the body) is no longer required. Evidence shows that shielding often provides no benefit for what is minimal to no gonadal dose, may not cover the organs such as ovaries despite adherence to appropriate techniques, can in some circumstances increase the overall dose of the examination, and can obscure necessary anatomy.18 Thus, in many radiology facilities, routine patient shielding is being discouraged.
Risks from medical radiation have been widely disseminated through the lay press over the last decade. Parents are concerned about the potentially harmful effects of diagnostic radiation on their children. This primer serves as an accessible resource to answer common queries pediatricians might receive from families, providing the most up-to-date information to have knowledgeable discussions about radiation risk.
- Hong JY, Han K, Jung JH, Kim JS. Association of exposure to diagnostic low-dose ionizing radiation with risk of cancer among youths in South Korea. JAMA Netw Open. 2019;2(9):e1910584. doi:10.1001/jamanetworkopen.2019.10584 [CrossRef] PMID:31483470
- Pearce MS, Salotti JA, Little MP, et al. Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumours: a retrospective cohort study. Lancet. 2012;380(9840):499–505. doi:10.1016/S0140-6736(12)60815-0 [CrossRef] PMID:22681860
- Miglioretti DL, Johnson E, Williams A, et al. The use of computed tomography in pediatrics and the associated radiation exposure and estimated cancer risk. JAMA Pediatr. 2013;167(8):700–707. doi:10.1001/jamapediatrics.2013.311 [CrossRef] PMID:23754213
- Huang WY, Muo CH, Lin CY, et al. Paediatric head CT scan and subsequent risk of malignancy and benign brain tumour: a nation-wide population-based cohort study. Br J Cancer. 2014;110(9):2354–2360. doi:10.1038/bjc.2014.103 [CrossRef] PMID:24569470
- Hendee WR, O'Connor MK. Radiation risks of medical imaging: separating fact from fantasy. Radiology. 2012;264(2):312–321. doi:10.1148/radiol.12112678 [CrossRef] PMID:22821690
- Hammer GP, Seidenbusch MC, Regulla DF, et al. Childhood cancer risk from conventional radiographic examinations for selected referral criteria: results from a large cohort study. AJR Am J Roentgenol. 2011;197(1):217–223. doi:10.2214/AJR.10.4979 [CrossRef] PMID:21701033
- Meulepas JM, Ronckers CM, Smets AMJB, et al. Radiation exposure from pediatric CT scans and subsequent cancer risk in the Netherlands. J Natl Cancer Inst. 2019;111(3):256–263. doi:10.1093/jnci/djy104 [CrossRef] PMID:30020493
- Mathews JD, Forsythe AV, Brady Z, et al. Cancer risk in 680,000 people exposed to computed tomography scans in childhood or adolescence: data linkage study of 11 million Australians. BMJ. 2013;346:f2360. doi:10.1136/bmj.f2360 [CrossRef] PMID:23694687
- Berrington de Gonzalez A, Salotti JA, McHugh K, et al. Relationship between paediatric CT scans and subsequent risk of leukaemia and brain tumours: assessment of the impact of underlying conditions. Br J Cancer. 2016;114(4):388–394. doi:10.1038/bjc.2015.415 [CrossRef] PMID:26882064
- Boice JD Jr., Radiation epidemiology and recent paediatric computed tomography studies. Ann ICRP. 2015;44(1)(suppl):236–248. doi:10.1177/0146645315575877 [CrossRef] PMID:25816281
- Ulsh BA. Are risks from medical imaging still too small to be observed or nonexistent?Dose Response. 2015;13(1):dose-response.14-030.Ulsh. doi:10.2203/dose-response.14-030.Ulsh [CrossRef] PMID:26673121
- Sadetzki S, Mandelzweig L. Childhood exposure to external ionising radiation and solid cancer risk. Br J Cancer. 2009;100(7):1021–1025. doi:10.1038/sj.bjc.6604994 [CrossRef] PMID:19337255
- Shahbazi-Gahrouei D, Gholami M, Setayandeh S. A review on natural background radiation. Adv Biomed Res. 2013;2(1):65. doi:10.4103/2277-9175.115821 [CrossRef] PMID:24223380
- American College of Radiology. ACR appropriateness criteria. Accessed August 25, 2020. https://www.acr.org/Clinical-Resources/ACR-Appropriateness-Criteria
- Hricak H, Brenner DJ, Adelstein SJ, et al. Managing radiation use in medical imaging: a multifaceted challenge. Radiology. 2011;258(3):889–905. doi:10.1148/radiol.10101157 [CrossRef] PMID:21163918
- Huang SY. Lifetime risk of developing or dying from cancer. Accessed September 1, 2020. https://www.cancer.org/cancer/cancer-basics/lifetime-probability-of-developing-or-dying-from-cancer.html
- National Council on Radiation Protection and Measurements. Medical Radiation Exposure of Patients in the United States. National Council on Radiation Protection and Measurements2019. NCRP Report 184
- Marsh RM, Silosky M. Patient shielding in diagnostic imaging: discontinuing a legacy practice. AJR Am J Roentgenol. 2019;212(4):755–757. doi:10.2214/AJR.18.20508 [CrossRef] PMID:30673332