Potential Complications of Lung Cancer Screening: Radiation Carcinogenesis:
Do CT scans cause cancer?
There is no direct evidence that low-dose CT scans, done in middle aged or elderly people, cause cancer.
There is some statistical evidence that higher cumulative doses from CT scans in children may have caused brain tumors or leukemia, but there is no data to show increased incidence or higher risk of cancer in older individuals.
If it were true that low-doses of radiation can cause cancer, there would, in any case, typically be a long delay before this occurred (more than twenty years).
What is the meaning of “radiation carcinogenesis?
It is well established that exposure to high doses of radiation can cause cancer. High dose exposure includes that from working with radioisotopes like radium (the “Radium Girls”), atomic bomb survivors (Hiroshima and Nagasaki), survivors of radiation accidents (Chernobyl), people who have undergone radiation therapy and people with long-term, cumulative exposure to radon gas in their homes.
Some scientists maintain that the very small dose of radiation from a low-dose CT scan can also cause cancer.
The formal name for this theory is the “linear, no-threshold theory.” This idea is based upon experiments by Nobel Prize winner Herman Muller in the 1940s- before it was even known that DNA was the genetic material. It has since been reported that Muller knew that there were errors in his assistant’s research, but did not correct them.
His research maintained that even very small amounts of radiation can cause mutations.
Others extrapolate this idea – since mutations are known to be the cause of cancer, small doses of radiation therapy can therefore cause cancer. One group of scientists working at the National Cancer Institute estimate, based upon a mathematical model, that as many as 1 in 120 people who have CT scans will get a major cancer; more than 20,000 persons would get cancer in the future because of the CT scan.
There is strong evidence showing that individuals over age 50 have a very small, statistically insignificant, risk of a later cancer, attributable to a low dose of radiation (below 100 milliSieverts) in a large cohort of unfortunate individuals in Hiroshima and Nagasaki exposed to atomic bomb radiation in 1945.
Another problem is that most physicists today agree that the linear no-threshold theory is wrong.
Normal human cells have mechanisms to repair minor injuries to DNA. Some even argue for the “hormesis” theory – that small doses of radiation may even be beneficial.
In the final analysis, probably at least one hundred million Americans have had CT scans over the past forty years. The number of cancers seen each year has gradually gone down – not up. If CT scans cause cancer, one would expect the opposite result – a substantial increase in the number of cancers.
Even if it were true that 1 in 120 people screened would get a major cancer many years later (it is almost certainly not true), there would still be a major benefit over risk as at least 1 in 10 people screened will benefit by early detection and cure of a lung cancer.
Complications of Screening: Get-rich-quick and Town and Gown