Risk of cancer related to parathyroid imaging negligible for both 4D CT and scintigraphy

The lifetime risk of developing cancer following parathyroid imaging using either 4D CT or scintigraphy is negligible and should not deter doctors from utilizing the modalities for preoperative assessments, according to study results published in the May issue of the American Journal of Roentgenology.

Patients with hyperparathyroidism can often benefit from preoperative imaging, which attempts to localize parathyroid adenomas through the use of a combination of ultrasound, parathyroid scintigraphy, and 4D CT, the latter of which is gaining ground as a preferred testing modality. But many have concerns about the safety of 4D CT, according to lead author Jenny Hoang, MD, and her colleagues from Duke University Medical Center. “One of the main arguments against the use of 4D CT for first-line imaging is that it may result in greater radiation exposure to the patient compared with parathyroid scintigraphy scans,” wrote Hoang et al. “Thus, the advantages of 4D CT should be carefully weighed against potential hazards associated with higher radiation exposure.”

To assess the nature of those potential hazards, Hoang and her team measured organ radiation doses for both 4D CT and scintigraphy on a phantom with metal oxide semiconductor field effect transistor detectors. The estimated dose was calculated for both modalities, which was used to estimate the potential lifetime risk of cancer for patients of various ages and sexes in line with the Biologic Effects of Ionizing Radiation VII report.

Their results showed that the thyroid received the highest dose of radiation from 4D CT at 151 mGy, with salivary glands receiving the second highest radiation dose at 138 mGy. For scintigraphy, the the colon (42 mGy), gallbladder (40 mGy), and kidneys (32 mGy) received the highest dose of radiation. The lifetime attributable cancer risk for the typical hyperparathyroidism patient was found to be 193 cancers/100,000 patients for 4D CT and 68 cancers/100,000 patients for scintigraphy. “The [estimated dose] of 4D CT is more than double that of scintigraphy,” the researchers concluded, “but both studies cause negligible increases in lifetime risk of cancer.”

Hoang and her team concluded that their research suggests the risk of developing cancer resulting from 4D CT or scintigraphy for parathyroid imaging is not significant enough to deter doctors from ordering preoperative scans. “Clinicians should not allow concern for radiation-induced cancer to influence decisions regarding workup in older patients.”