CT Radiation and Cancer Risk

Whether computed tomographic (CT) radiation really induces cancers remains controversial. However, in children and adolescents, the association between CT radiation and carcinogenesis seems plausible given the supporting results of multiple large epidemiological studies. A recent study suggests perioperative abdominopelvic CT radiation is associated with a higher incidence of hematologic malignant neoplasms. The study findings are published in the JAMA Surgery on January 20, 2021.

Patients with acute appendicitis make up a very relevant target population for the investigation of carcinogenic risk of CT. Appendicitis is the most common benign disease with a reported incidence of 100 to 206 per 100,000 person-years. Even if the carcinogenic risk of CT is very small, the risk in such a large number of exposed patients may lead to a measurable number of excess cancers. Red bone marrow is the most radiosensitive tissue, and the carcinogenic risk of hematologic malignant neoplasms from ionizing radiation has been of particular concern. Besides, more than 10% of whole-body red bone marrow is distributed in os coxae, which is covered by abdominopelvic CT. To evaluate this further, researchers conducted a study and measured the risk of hematologic malignant neoplasms after perioperative abdominopelvic CT in patients who underwent appendectomy for appendicitis in South Korea.

It was a nationwide population-based cohort study in which researchers used the National Health Insurance Service claims database in South Korea to assess 825,820 patients who underwent appendectomy for appendicitis from January 1, 2005, to December 31, 2015, and who had no underlying risk factors for cancer. They divided the patients into CT-exposed (n = 306,727) and CT-unexposed (n = 519,093) groups. The major outcome assessed was the incidence rate ratio (IRR) of hematologic malignant neoplasms for both groups. IRR of abdominopelvic organ cancers and IRR of all cancers were also assessed. Researchers used Poisson regression models with adjustment for age and sex to calculate the IRR.

Key Findings of the Study

• Researchers observed the development of hematologic malignant neoplasms in 323 patients in the CT-exposed group during 1,486,518 person-years and 500 patients in the CT-unexposed group during 3,422,059 person-years.
• They noted that for all hematologic malignant neoplasms, the IRR for the CT-exposed vs CT-unexposed group was 1.26.
• They also noted that incidence of hematologic malignant neoplasms tended to increase with the number of abdominopelvic CT examinations.
• They found that the carcinogenic risk from abdominopelvic CT radiation was most pronounced in patients aged 0 to 15 years (IRR, 2.14).
• In terms of individual categories of hematologic malignant neoplasms, they found the CT-exposed group had an elevated risk only for leukemia (IRR, 1.40).
• However, they found no difference between groups in the incidence rate of abdominopelvic organ cancers (IRR, 1.07) and that of all cancers (IRR, 1.04).

The authors concluded, "This study controlled for reverse causation bias by defining the reasons for CT scan, and findings suggest that abdominopelvic CT radiation is associated with a higher incidence of hematologic malignant neoplasms. Efforts should be continued for judicious use of CT examinations".

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