Oncology (General Cancer)/radiation

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QUESTION: hello, I am a 27 year old female and last july of 2014, I had to get a abdominal and pelvis ct scan and ten days later a barium swallow, then last week I had to get a chest ct scan. I have read on the internet that ct scans cause cancer even if you only get one and now I am super worried and scared. could you please tell me what the percentage is of getting cancer from all this radiation. my doctor told me that I probably receieved around 20 msv of radiation. thank you

ANSWER: You ask a very complicated question.  The short answer is that if you look at a population of people who have received 20 msv of radiation (between ages 16 and 65) that population will have 1/2000 increase in risk over a population that never got that radiation and is otherwise the same.  There have been many studies and they all show slight increases in risk, the more radiation you have received, but remember, these are population based.  It doesn't mean that you yourself will get cancer.  In general diagnostic radiation is pretty safe, and the risk of cancer starts to show up about five years after exposure, increases slightly over the next fifteen years, then levels off.  
What can you do about it?  We have good evidence that exercise (aerobic exercise, meaning running, bicycling, swimming), keeping near ideal weight, a diet high in plants and antioxidants all may help reduce cancer risk in people.  This goes for those who have had radiation exposure as well.  So don't worry.  

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QUESTION: So in other words, the chance of that happening is pretty small then right? I just worry because I am overweight and I am also exposed to second smoke so I'm afraid that this radiation will cause cancer because of the other things

Answer
Chances are very small. In fact a bad sunburn in a teenager is probably higher risk for developing skin cancer later in life.  Second hand smoke poses a low but real risk as well.  Obesity is a risk factor for some kinds of cancer.  And to top it all off, the genetic makeup you have been born with is related to your cancer risk.  The point is, you can't avoid cancer risks but you can do things to minimize your own risk, and that's about it.  There is some recent very interesting data on disease risk reduction via the "Fast Mimicking Diet".   We've known for a long time that most diseases associated with aging (cancer, heart disease, alzheimer's, etc) can be reduced in animals and human beings if the calory intake is less than the amount needed to maintain current weight, or, if you are 20 % under your "ideal" weight, the intake needed to stay there.  This has been shown over and over in animals, and there is a lot of evidence that it works for people as well.  Recently a huge study suggested that if you reduce your intake to this level five days in a row every month to every two or three months, most of the changes that you see in fasting animals still happen.  I'm beginning such a diet this week.  Hope this helps.  

Oncology (General Cancer)

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Donald Higby, M.D.

Expertise

I can answer almost all questions related to the treatment and natural course of most kinds of cancer, especially cancers of prostate, colon, lung and breast.

Experience

I have been a practicing medical oncologist for 36 years, and have been chief of service at a major medical center for 25 years. I've also done research in cancer treatments.

Organizations
American Society of Clinical Oncology

Publications
New England Journal of Medicine American Journal of Medicine Journal of the American Society of Clinical Oncology Hematology Transfusion Medicine

Education/Credentials
MD, Stanford University Internal Medicine residency, St. Louis University School of Medicine, St. Louis, MO Medical Oncology Fellowship, Roswell Park Cancer Institute, Buffalo, NY

Awards and Honors
America's Best Physicians, last 14 years

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