AJR: Low-dose x-ray in kids does not increase cancer risk
Children exposed to low doses of x-ray radiation do not exhibit higher rates of cancer, a valuable empirical insight that can supplement theoretic radiation models and inform pediatricians, according to a large German study published in the July issue of the American Journal of Roentgenology.
Studies of atomic bomb survivors continue to anchor most assessments of pediatric cancer risks generated by ionizing radiation from medical imaging. But these largely theoretic models, which tend to lack individual dosimetry, are “associated with great uncertainty,” noted Gaël P. Hammer, from the Institute for Medical Biostatistics, Epidemiology and Informatics at Johannes Gutenberg University Medical Center in Mainz, Germany, and colleagues.
Hammer and co-authors reviewed the records of 78,527 children who underwent x-ray exams between 1976 and 2003 at a large academic hospital in Munich. The researchers assessed the association between exposure to low-dose x-ray and cancer rates, excluding all patients with previous diagnoses of cancer and any patients who underwent CT or had cumulative doses of 10 mSv or higher.
A total of 68 cancers were identified in the study cohort, yielding a standardized incident ratio of 0.97 based on the population-based estimate that 70 patients would experience cancer. The mean follow-up consisted of 7.4 years.
The median cumulative effective dose for all patients was 5 uSv (0.005 mSv), while 692 patients received cumulative effective doses above 1 mSv. Sixty-three percent of patients underwent only one x-ray over the study period, while 19 percent received two exams, 8 percent underwent three exams and the remaining 11 percent were imaged four or more times with x-ray. One patient received 85 x-ray exams.
The risk of cancer among the cohort did not differ significantly by gender, exam indication or according to type of cancer, with the exception of patients with congenital malformations and in the group referred for endocrine disease. The authors called the latter association “spurious,” assessing a 20-fold increase in cancer resulting from increased radiation exposure, from 0.12 to 0.78 mSv, as “highly unlikely,” especially considering the uniformity of the researchers’ other findings.
“To our knowledge, this study is the first epidemiologic cohort study in which cancer risk among children exposed to diagnostic radiation was investigated with a detailed individual dose history,” Hammer and colleagues explained.
“The results suggest that childhood exposure to diagnostic x-rays is not linked to an appreciable increase in the incidence of solid tumors or leukemia in this cohort. The dose-response analysis did not reveal a trend toward increasing cancer risk with increasing dose.”
Hammer and co-authors noted that the median cumulative effective dose of 0.001 mSv was dramatically lower than experts’ estimates that natural radiation exposure in Germany reaches 2.4 mSv annually per person. Moreover, the hospital’s effective dose declined by 15 uSv over the study period as a result of increased beam filtration and improved procedures, the authors added.
Hammer and colleagues credited these dose-reduction techniques and improvements in equipment and internal documentation as essential not only to limiting dosage caused by x-ray, but also in making their large-scale epidemiological study possible. An important next step, they noted, is a comprehensive evaluation of CT radiation exposure and cancer incidence.
Studies of atomic bomb survivors continue to anchor most assessments of pediatric cancer risks generated by ionizing radiation from medical imaging. But these largely theoretic models, which tend to lack individual dosimetry, are “associated with great uncertainty,” noted Gaël P. Hammer, from the Institute for Medical Biostatistics, Epidemiology and Informatics at Johannes Gutenberg University Medical Center in Mainz, Germany, and colleagues.
Hammer and co-authors reviewed the records of 78,527 children who underwent x-ray exams between 1976 and 2003 at a large academic hospital in Munich. The researchers assessed the association between exposure to low-dose x-ray and cancer rates, excluding all patients with previous diagnoses of cancer and any patients who underwent CT or had cumulative doses of 10 mSv or higher.
A total of 68 cancers were identified in the study cohort, yielding a standardized incident ratio of 0.97 based on the population-based estimate that 70 patients would experience cancer. The mean follow-up consisted of 7.4 years.
The median cumulative effective dose for all patients was 5 uSv (0.005 mSv), while 692 patients received cumulative effective doses above 1 mSv. Sixty-three percent of patients underwent only one x-ray over the study period, while 19 percent received two exams, 8 percent underwent three exams and the remaining 11 percent were imaged four or more times with x-ray. One patient received 85 x-ray exams.
The risk of cancer among the cohort did not differ significantly by gender, exam indication or according to type of cancer, with the exception of patients with congenital malformations and in the group referred for endocrine disease. The authors called the latter association “spurious,” assessing a 20-fold increase in cancer resulting from increased radiation exposure, from 0.12 to 0.78 mSv, as “highly unlikely,” especially considering the uniformity of the researchers’ other findings.
“To our knowledge, this study is the first epidemiologic cohort study in which cancer risk among children exposed to diagnostic radiation was investigated with a detailed individual dose history,” Hammer and colleagues explained.
“The results suggest that childhood exposure to diagnostic x-rays is not linked to an appreciable increase in the incidence of solid tumors or leukemia in this cohort. The dose-response analysis did not reveal a trend toward increasing cancer risk with increasing dose.”
Hammer and co-authors noted that the median cumulative effective dose of 0.001 mSv was dramatically lower than experts’ estimates that natural radiation exposure in Germany reaches 2.4 mSv annually per person. Moreover, the hospital’s effective dose declined by 15 uSv over the study period as a result of increased beam filtration and improved procedures, the authors added.
Hammer and colleagues credited these dose-reduction techniques and improvements in equipment and internal documentation as essential not only to limiting dosage caused by x-ray, but also in making their large-scale epidemiological study possible. An important next step, they noted, is a comprehensive evaluation of CT radiation exposure and cancer incidence.