Radiation epidemiology and recent paediatric computed tomography studies

Abstract

Abstract-Recent record-linkage studies of cancer risk following computed tomography (CT)procedures among children and adolescents under 21 years of age must be interpreted with caution. The reasons why the examinations were performed were not known, and the dosimetric approaches did not include individual dose reconstructions or account for the possibility for missed examinations. The recent report (2013) on children by the United Nations Scientific Committee on the Effects of Atomic Radiation concluded that the associations may have resulted from confounding by indication (also called 'reverse causation'), and not radiation exposure. The reported cancer associations may very well have been related to the patients' underlying health conditions that prompted the examinations. Reverse causation has been observed in other epidemiological investigations, such as a Swedish study of thyroid cancer risk following I-131 scintillation imaging scans, and in studies of brain cancer risk following Thorotrast for cerebral angiography. Epidemiological patterns reported in the CT studies were also inconsistent with the world's literature. For example, in a UK study, teenagers had a higher risk of brain tumour than young children; in an Australian study, cancers not previously linked to radiation were significantly elevated; and in a Taiwanese study, the risk of benign tumours decreased with age at the time of CT examination. In all studies, solid tumours appeared much earlier than previously reported. Remarkably, in the Australian study, brain cancer excesses were seen regardless of whether or not the CT was to the head, i.e. a significant excess was reported for CT examinations of the abdomen and extremities, which involved no radiation exposure to the brain. In the UK study, the significance of the 'leukaemia' finding was only because myelodysplastic syndrome was added to the category, and there was no significance for leukaemia alone. Without knowledge of why CT examinations were performed, any future studies will be equally difficult to interpret. It is noteworthy that two recent studies of children in France and Germany found no significant excess cancer risk from CT scans once adjustment was made for conditions that prompted the scan, family This paper does not necessarily reflect the views of the International Commission on Radiological Protection. 236 history, or other predisposing factors known to be associated with increased cancer risk. Nonetheless, such studies have heightened awareness of these relatively high-dose diagnostic procedures, and the need to reduce unnecessary examinations and lower the dose per examination commensurate with the desired image quality.

Confounding of the Association between Radiation Exposure from CT Scans and Risk of Leukemia and Brain Tumors by Cancer Susceptibility Syndromes

“…[8][9][10][11][12][13]. Confounding by indication occurs if the reason for a CT scan is associated with cancer risk.…”

Dose Optimization to Minimize Radiation Risk for Children Undergoing CT and Nuclear Medicine Imaging Is Misguided and Detrimental

“…. .once adjustment was made for conditions that prompted the scan, family history, or other predisposing factors known to be associated with increased cancer risk" (13). Thus, confounding by indication (reverse causation) must be ruled out completely, or observed excess cancer risk may be falsely, and facilely, attributed to CT exposure.…”

Radiation-induced senescence and thyroid cancer: a barrier or a driving force

“…29 Based on these findings, one aspect to consider is the worldwide increase in medical radiation exposure 30 and the influence of these low-doses in radiosensitive organs as thyroid. Several studies successfully correlated number and radiation dose of CT Scans for infants and adolescents to a greater thyroid cancer risk, 29,31,32 especially in females. Another relevant question is whether genetic alterations could predispose to radiation carcinogenic actions.…”