Projected Lifetime Cancer Risks From Current Computed Tomography Imaging is a study just published in JAMA Internal Medicine. The study concludes: “That at current utilization and radiation dose levels, CT examinations in 2023 were projected to result in approximately 103,000 future cancers over the course of the lifetime of exposed patients. If current practices persist, CT-associated cancer could eventually account for 5% of all new cancer diagnoses annually.” The study can be downloaded below.
CT exposes the patient to ionizing radiation which increases the likelihood of subsequent development of cancer directly proportional to the dose of radiation delivered by the study. The authors of this study estimated the lifetime radiation-induced rate of cancer by using a number of models that are not readily available to the reader. They did not do a longitudinal long term tally of cancer incidence in patients who underwent CT scanning. Such a study would take decades to do and be almost impossible to perform.
The assumptions that the researchers used are reasonable and their conclusions equally reasonable. If we accept their extrapolation of radiation dose from other sources like that obtained from the Japanese exposed to radiation following the drop of two atomic bombs at the end of World War II and other studies linking radiation to cancer then their conclusions seem reasonable.
“An estimated 61,510 000 patients underwent 93, 000,000 CT examinations in 2023, including 2,570,000 (4.2%) children, 58,940,000 (95.8%) adults, 32,600,000 (53.0%) female patients, and 28,910 ,00 (47.0%) male patients. Approximately 103,000 radiation-induced cancers were projected to result from these examinations.”
What should a patient, or a physician for that matter, take away from this study? Obviously, do not order diagnostic studies that carry a risk greater than any likely benefit. You would think this admonition unnecessary, but it’s not. Physicians order CTs without much thought as to their risk. Patients rarely see CTs as carrying any risk.
One of the study’s authors said in an interview, “Our estimates put CT on par with other significant risk factors, such as alcohol consumption and excess body weight. “Reducing the number of scans and reducing doses per scan would save lives.”
The projected number of radiation-induced cancers in this analysis is 3 to 4 times higher than the earlier assessment of CT exposure for several reasons. First, while growth in utilization has slowed, CT use is 30% higher today than in 2007, due to growth in low-value, potentially unnecessary imaging as well as population aging. Second, dose modeling in this study accounted for multiphase scanning, which occurs in 28.5% of examinations but was not modeled in a prior study, as multiphase frequency was unknown. Third, the substantially higher organ doses in this study were reconstructed using newer dosimetry methods with examination-level data from more than 120,000 actual examinations, while the a study modeled doses from national survey data or imaging protocols and assumed examinations in children were performed using pediatric-specific settings. Lastly, the investigators included more granular CT categories reflecting imaging indications that have important dose differences. The total projected lifetime cancer incidence by sex and age at exposure is shown in the figure below.
There are times when a CT is of critical diagnostic importance. This study just emphasizes that good judgment is as important when ordering a diagnostic test as it is in any medical encounter. The command, “First do no harm” is as relevant today as it was two millennia ago.
As a retired physician who was an academic I’ve read countless research reports, as you have too. Some of them were and are clearly worthless, some are of dubious worth or utility, some need the test of time or repeat studies for corroboration, and some are priceless gems.
What are the most annoying because as you note virtually unprovable in most nations are extrapolations based upon of all things extremes like the post atom bomb stats. And then the research almost demands that physicians change how they order or do radiological exams based upon these unproven assertions of definite dramatic numbers of increased cancers. You assume as the authors do that radiological effects are in a straight line on a graph from smallest measurable exposure to dramatically large exposures, something which has never been proven. What these studies are effective at accomplishing is (1)frightening patients and doctors into avoiding radiographic studies they may actually need, (2)whetting the appetite of class action suit happy lawyers, and (3)increasing costs via increased paperwork for radiographic studies.