[ RadSafe ] Decades after Childhood Radiation, Thyroid Cancer a Concern

[ROY HERREN]

http://www.urmc.rochester.edu/news/story/index.cfm?id=3075
 
Decades after Childhood Radiation, Thyroid Cancer a Concern
December 16, 2010
When children are exposed to head and neck radiation, whether due to cancer 
treatment or multiple diagnostic CT scans, the result is an increased risk of 
thyroid cancer for the next 58 years or longer, according to University of 
Rochester Medical Center research.
The study is believed to be the longest of any group of children exposed to 
medical irradiation and followed for thyroid cancer incidence. It was published 
in the December 2010 edition of the journal, Radiation Research.
The data also might provide some insight about why the rates of thyroid cancer 
continue to rise, as the general public is increasingly exposed to higher doses 
of radiation through more frequently used imaging tests such as computed 
tomography (CT), said lead author Jacob Adams, M.D., M.P.H., an associate 
professor in the Department of Community and Preventive Medicine at URMC
“Ionizing radiation is a known carcinogen and, in fact, about 1 million CT scans 

are performed every year on children five years or younger,” Adams said. 
“Although CTs and other imaging tests are an important diagnostic tool and 
radiotherapy is an important treatment modality for cancer, with everything 
comes a risk. Our study attempted to measure the very long-term impact on 
thyroid cancer from medical irradiation. Our findings strongly suggest that 
those individuals exposed to irradiation from multiple CT scans to the head, 
neck and chest during early childhood and individuals treated with radiotherapy 
to the upper body as children have a lifelong increased risk of thyroid cancer.”
Adams and colleagues indirectly evaluated the future risks of modern patients by 

assessing the rates of thyroid cancer in a group that was treated with 
lower-dose chest radiotherapy in Rochester, N.Y., between 1953 and 1987. The 
cohort had been treated during infancy for an enlarged thymus, a condition that 
physicians used to believe was a health problem. None of the radiation 
administered was for cancer, and thus the research is not confounded by a 
susceptibility to the disease.
Adams re-surveyed the population between 2004 and 2008, and compared the health 
status of the group to their siblings who had not received radiation. Thyroid 
cancer occurred in 50 of the 1,303 irradiated patients compared to only 13 of 
the 1,768 siblings. The association between radiation and thyroid cancer 
remained strong even after researchers accounted for other factors that could 
contribute to thyroid cancer risk.
Radiation doses in the mid-century group overlapped with current medical 
practices; however, in general, higher doses and less precision were used years 
ago. Doses at the lower end of the study cohort were comparable to a diagnostic 
pediatric chest CT given today, the study said. Not surprisingly, researchers 
found that thyroid cancer risk increased with higher doses of radiation.
The Rochester study confirmed the findings of a pooled review of five earlier 
population studies, and adds to the literature by showing that, at least in 
children, the risk of cancer due to radiation exposure continues for a median of 

57.5 years.
The James P. Wilmot Cancer Center at URMC and the National Heart Lung and Blood 
Institute funded the study.
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