Health Effects of Ionizing Radiation

What is Ionizing Radiation? 

Medical imaging is used for both diagnostic and therapeutic purposes, which is fundamental in the treatment of children. Ionizing radiation is used in many medical imaging procedures, including X-rays, fluoroscopy, nuclear medicine (also known as nuclear imaging), and computed tomography (CT). Before jumping into ionizing radiation related to medical imaging, we need to know what ionizing radiation is.  

Current Pediatric Imaging Status 

The use of medical radiation imaging has increased almost sixfold in recent decades. Despite the fact that the dosage administered during each examination has decreased, the overall collective dosage over a series of radiation exposures continues to rise along with the number of tests and procedures conducted. Further, effective radiation doses are higher in most CT exams than in conventional radiography procedures. Depending on the cause and age, diagnostic imaging doses in children range from 0.01 mSv for a standard frontal chest x-ray to roughly 5–10 mSv for an abdomen/pelvis CT. 

Sv, or sievert, is an international unit that describes radiation health effects for a population. A millisievert, or mSv, is 0.001 sievert.

According to a report by the National Council on Radiation Protection and Measurements (NCRP) made in 2016, CT scans accounted for 84% of effective medical imaging exposure in children, and radiography for 86% of total medical imaging studies on children. Heads account for 55% of pediatric CT exams, abdomen/pelvis is second at 25%, spine is third at 10%, and the remaining 10% is split between the chest and other regions.

Diagnostic Radiation Exposure on the Head 

One-third of all diagnostic radiation exposures are through cranial imaging. Despite the low radiation doses, children may be more vulnerable to radiation-induced cancer than adults due to the susceptibility of brain tissue to cytotoxic damage from ionizing radiation (IR). In addition, conditions that necessitate repeated CT scans, such as traumatic brain injury or cerebrospinal fluid shunts, expose children to cumulative radiation, increasing cancer risks. 

Scientists estimated there to be one extra malignancy for every 1,428 CT scans in 2001. Since 2012, five large-scale epidemiological studies have found an elevated prevalence of neoplasms (brain tumors) in children exposed to head CTs. Further, two studies found a dose-dependent relationship between tumor incidences and CT exposure, with Krille et al. indicating a dose-dependent rise in brain tumor incidences with the number of head CT scans. 

This finding was confirmed in a recent study that used three pediatric head phantoms to quantify radiation exposures. The findings of this study revealed that cancer diagnoses and mortality were inversely related to age, and CT scans may be linked to a 0.16% increase in cancer risk per 500 children. It is worth mentioning that the risk estimations in this study have numerous limitations, such as differences in pediatric phantoms and dosage variation. 

Despite new evidence of links between CT tests and tumors, linking head CT scans to tumor incidences is hampered by the risk of reverse causation. When compared to an un-scanned population, patients who undergo head CTs are more likely to have pre-existing neoplasms or underlying disorders that enhance their baseline risk of malignancy. As a result, assuming head-CT patients have the same cancer risks as non-head-CT people may exaggerate the cancer risk attributable to CTs, especially in studies with short follow-up periods and few malignancies. 

Important Notes 

It is important to mention that these studies had some limitations, causing the risk of cancer to be unpredictable at the individual level. First, the primary data is usually derived from large-scale epidemiology investigations. Variations in each subject have a significant impact on forecasts of cancer risks, such as dose-response and patient variability. The underlying condition and life expectancy are also more unknown due to the extended radiation-induced cancer latency. The mistake in predicting an individual's cancer risk from the radiation of a CT scan is believed to be 500% or higher.  

In addition, IR exposure can be caused through medical imaging, but it can also occur naturally, such as from cosmic, solar, or terrestrial radiation or Radon gas. Medical radiation exposure in children accounts for just 9% of total radiation exposure in the United States each year, and radiation-induced cancers occur in the same group as spontaneous cancers, making it even more difficult to attribute individual cancer risks to medical imaging rather than to natural causes. 

However, despite the fact that these limitations of study exist, we may nevertheless apply such results as a warning to protect children from unnecessary radiation. Further study into cancer risks in medical imaging procedures is needed in the future to better balance possible cancer risks with treatment. 

Reference:

Abalo, K. D., Rage, E., Leuraud, K., Richardson, D. B., Le Pointe, H. D., Laurier, D., & Bernier, M. O. (2021). Early life ionizing radiation exposure and cancer risks: systematic review and meta-analysis. Pediatric radiology, 51(1), 45-56. 

Brenner, D. J., Elliston, C. D., Hall, E. J., & Berdon, W. E. (2001). Estimated risks of radiation-induced fatal cancer from pediatric CT. American journal of roentgenology, 176(2), 289-296. 

Brenner, D. J., & Hall, E. J. (2007). Computed tomography—an increasing source of radiation exposure. New England journal of medicine, 357(22), 2277-2284. 

Frush, D. P., & Perez, M. D. R. (2017). Children, medical radiation and the environment: An important dialogue. Environmental research, 156, 358-363. 

Guillerman, R. P. (2014). From ‘Image Gently’to image intelligently: a personalized perspective on diagnostic radiation risk. Pediatric radiology, 44(3), 444-449. 

Haramati, L. B. (2008). Ethical trials to determine the risks and benefits of radiation exposure from coronary CT angiography. Journal of the American College of Radiology, 5(10), 1073-1076. 

Huang, W. Y., Muo, C. H., Lin, C. Y., Jen, Y. M., Yang, M. H., Lin, J. C., ... & Kao, C. H. (2014). Pediatric head CT scan and subsequent risk of malignancy and benign brain tumour: a nation-wide population-based cohort study. British journal of cancer, 110(9), 2354-2360. 

Journy, N., Rehel, J. L., Ducou Le Pointe, H., Lee, C., Brisse, H., Chateil, J. F., ... & Bernier, M. O. (2015). Are the studies on cancer risk from CT scans biased by indication? Elements of answer from a large-scale cohort study in France. British journal of cancer, 112(1), 185-193. 

Krille, L., Dreger, S., Schindel, R., Albrecht, T., Asmussen, M., Barkhausen, J., ... & Blettner, M. (2015). Risk of cancer incidence before the age of 15 years after exposure to ionising radiation from computed tomography: results from a German cohort study. Radiation and environmental biophysics, 54(1), 1-12. 

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Mathews, J. D., Forsythe, A. V., Brady, Z., Butler, M. W., Goergen, S. K., Byrnes, G. B., ... & Darby, S. C. (2013). Cancer risk in 680 000 people exposed to computed tomography scans in childhood or adolescence: data linkage study of 11 million Australians. Bmj, 346. 

Mettler, F. A., Mahesh, M., Chatfield, M. B., Chambers, C., Elee, J., & Frush, D. (2019). Report No. 184—medical radiation exposure of patients in the United States (2019). National Council on Radiation Protection and Measurements, Bethesda. 

Pearce, M. S., Salotti, J. A., Little, M. P., McHugh, K., Lee, C., Kim, K. P., ... & De González, A. B. (2012). Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumours: a retrospective cohort study. The Lancet, 380(9840), 499-505. 

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Saeed, M. K., & Almalki, Y. (2021). Assessment of computed tomography radiation doses for pediatric head and chest examinations using pediatric phantoms of three different ages. Radiography, 27(2), 332-339. 

Sheppard, J. P., Nguyen, T., Alkhalid, Y., Beckett, J. S., Salamon, N., & Yang, I. (2018). Risk of brain tumor induction from pediatric head CT procedures: a systematic literature review. Brain tumor research and treatment, 6(1), 1-7. 

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