Some basics about radiation and cancer

Editor’s note: Two studies in the Dec 14-28, 2009 issue of Archives of Internal Medicine have found that CT scans each year may cause tens of thousands of future cancer cases. Amy Berrington de González, D. Phil., of the National Cancer Institute, Bethesda, Md., and colleagues found CT scans performed in 2007 could lead to development of about 29,000 future cancers including 14,000 cases from scans of the abdomen and pelvis which require higher dosages of radiation; 4100 from chest scans; 4,000 from head scans; and 2,700 from CT angiography. The following are some basics for those who know a thing about radiation and cancer.

Understand radiation cancer risk

Is radiation a cancer-causing agent or carcinogen?

Yes, ionizing radiations like x-ray used in computed tomography scan or CT scan are recognized by the U.S. National Toxicology Program as a carcinogen.  In fact, radiation is the most studied carcinogen in history.

Is there any threshold of exposure to radiation that is considered safe?

Safe or not, it all depends on your definition.  One needs to know that just because you are exposed to some radiation does not mean you will definitely get cancer. On the other hand, no one can guarantee that you will not get cancer after you receive certain dose of radiation from a CT scan or conventional x-ray diagnostic tool.

It has become clear that any tiny amount of radiation can cause mutations, which of course may or may not lead to development of cancer.

In addition, people may need to remember that radiation-induced damage is cumulative over the years.
 
In a sense, there is no safety threshold for radiation.

How does radiation cause damage to DNA?

Radiation causes ionizations in molecules in living cells, which injure the cells.  The radiation-induced damage may or may not be repaired.  Cells receiving severe damage may just die, which would not result in any consequence in the future. The problem with radiation is that some injured cells cannot be repaired and they will produce abnormal cells particularly in children, which may lead to development of cancer.

We receive background radiation every day.  Do we have to worry about medical radiation?

There are a couple of things different between the two types.  Medical radiaiton comes often in a higher dose than that of environmental radiation. For instance, one may get background radition in 300 MREM in a year. But one chest-ray gets you 30 or 50 MREM. One CT scan can be 50 to 100 times higher than chest x-ray.

And secondly, according to John Gofman, MD PhD, a distinguished nuclear physicist and medical physician, medical radiation poses twice as effective as the radiation from our environment at causing damage.  Medical radiation is more focused and results in more severe injury to cells.

Do all medical radiations pose the same cancer risk?

No. The risk depends on dosage, the dose rate, age, sex, lifestyle and the individual's genetics among other things.

Some medical tools like CT scans use much higher doses than chest x-ray.  CT scan performed on abdomen/pelvic uses higher doses of radiation than that used for the head.

Who are at higher risk of radiation-induced cancer?

Children are at higher risk of radiation-induced cancer.