January 14, 2020
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CT scans linked to higher risk for certain cancers

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Adults in Taiwan exposed to radiation from CT scans demonstrated increased risk for thyroid cancer and leukemia, according to results of a nested case-control study published in JNCI Cancer Spectrum.

Researchers also observed a dose-response association for thyroid cancer, leukemia and non-Hodgkin lymphoma among those aged 45 years and younger.

“CT scans are widely used, but some may be unnecessary,” Yu-Hsuan Shao, MHS, PhD, researcher at the Graduate Institute of Biomedical Informatics of the College of Medical Science and Technology at Taipei Medical University in Taiwan, told Healio. “Studies show that CT scan exposure before age 19 years increases the risk for leukemia, brain cancer and other cancer types, including leukemia and non-Hodgkin lymphoma. We aimed to examine whether these risks were accurate.”

The study by Shao and colleagues included adults from a population-based universal health insurance data set in Taiwan between 2000 and 2013. The researchers identified exposure to radiation from CT scans through physician order codes in medical insurance records. They defined the exposure window as the period from the date of the first CT scan to 3 years prior to a cancer diagnosis.

Overall, the investigators identified 22,853 thyroid cancer cases, 13,040 leukemia cases and 20,157 non-Hodgkin lymphoma cases. They matched all cases with controls.

CT scan equipment 
Radiation dose appeared positively associated with risk for thyroid cancer, leukemia and non-Hodgkin lymphoma among those aged 45 years and younger.
Source: Adobe Stock

Results showed associations between radiation exposure from CT scans and increased risk for thyroid cancer (OR = 2.55; 95% CI, 2.36-2.75) and leukemia (OR = 1.55; 95% CI, 1.42-1.68). Women demonstrated a higher risk than men for thyroid cancer (OR = 2.76; 95% CI, 2.53-3.02 vs. 2.04; 95% CI, 1.75-2.37) and leukemia (OR = 1.82; 95% CI, 1.6-2.07 vs. 1.39; 95% CI, 1.25-1.55).

Radiation exposure from CT scans did not appear to be associated with non-Hodgkin lymphoma (OR = 1.05; 95% CI, 0.98-1.12) in an analysis that combined patients of all ages. However, researchers did observe a 2.72-fold increased risk for non-Hodgkin lymphoma among those aged 35 years and younger and a threefold increased risk among those aged 45 years and younger.

Moreover, radiation dose appeared positively associated with risk for thyroid cancer, leukemia and non-Hodgkin lymphoma (P < .001 for all) among those aged 45 years and younger.

“CT scan is still an important diagnostic tool. However, we may want to use this tool with caution and avoid unnecessary scans,” Shao told Healio. “We may conduct additional research to examine whether low-dose CT scans increase cancer risk in this patient population.” – by Jennifer Southall

For more information:

Yu-Hsuan Shao, MHS, PhD, can be reached at Taipei Medical University, 26 172-1 Section 2, Keelung Road, Taipei, Taiwan; email: jonishao@tmu.edu.tw.

Disclosures: The authors report no relevant financial disclosures.