New research strengthens the body of evidence demonstrating a high risk of blood cancer from exposure to low doses of radiation from CT scans.
According to the results, for every 10,000 children examined with an average low dose of 8 milligray (mGy), one to two will likely develop a hematological malignancy related to radiation exposure over the next 12 years.
The findings were published online in Nature Medicine, are based on more than 1.3 million CT scans in nearly 900,000 individuals younger than 22 years old when scanned.
Peter Marsden, PhD, and Jim Thurston, radiation protection experts at Dorset County Hospital, NHS Foundation Trust, said that, this study makes an important contribution to the understanding of the effects of ionizing radiation, specifically X-rays, on the human body at the levels of radiation exposure encountered in diagnostic CT procedures.
These findings highlight levels of risk which align with those currently estimated and do not suggest that the use of CT carries a greater risk than previously thought.
Exposure to moderate- (≥ 100 mGy) to high-dose (≥ 1 Gy) ionizing radiation is a well-established risk factor for leukemia in both children and adults. However, the risk related with low-dose exposure (< 100 mGy) typically connected with diagnostic CT exams in children and teens remains unclear.
The present study, coordinated by the International Agency for Research on Cancer, aimed to improve direct estimates of cancer risk from low-dose radiation exposure from CT scans performed in childhood and adolescence. The researchers estimated radiation doses to the active bone marrow based on body part scanned, patient characteristics, time period, and inferred CT technical parameters.
Overall, the analysis included 876,771 young individual who underwent roughly about 1.3 million CT scans.
During the follow up, a total of 790 hematological malignancies, including lymphoid and myeloid malignancies, were identified. More than half (51%) of the cases were diagnosed in individuals under the age of 20 and 88.5% were diagnosed in individuals under age 30 years.
The observational study found about twofold excess risk of all hematological malignancies per 100 mGy in children, adolescents, and young adults, with similar risk estimates observed for lymphoid and myeloid cancers. The excess relative risk for hematological malignancies increased as the number of CT exams increased — with risk increasing by 43% per exam.
The results of this study strengthen the findings from previous low-dose studies of a consistent and robust dose-related high risk of radiation-induced hematological malignancies and highlight the importance of optimizing doses in this patient population, says study author Elisabeth Cardis, PhD, with Barcelona Institute for Global Health (ISGlobal) in Barcelona, Spain, and colleagues.
This publication specifies that there could be a small cancer risk from CT scans in young individuals, but it is important for this to be seen in the context of the substantial benefit these scans bring, due to the important diagnostic information they provide.
The above statement was said by Sarah McQuaid, PhD, chair of the nuclear medicine special interest group and Institute of Physics and Engineering in Medicine, York, UK.
