Answer to Question #11147 Submitted to "Ask the Experts"

Category: Medical and Dental Patient Issues — Diagnostic X Ray and CT

The following question was answered by an expert in the appropriate field:

Q

I hope you can help me to clarify this question since I am very worried. I have undergone a series of x rays and CT (computerized tomography) scans with a dose around 20 mSv over 15 years.  According to the HPS Position Statement Radiation Risk in Perspective, doses under 100 mSv received over many years are not dangerous.

But I have found out that smoking also delivers a very high dose of radiation. I have smoked for 14 years around five cigarettes per day. I quit about five years ago. According to the information I have found I have accumulated more than 400 mSv of radiation from the years I used to smoke. Is cigarette smoking included when calculating the individual radiation dose received over the years? And is it also considered when establishing the radiation safety limits?

I understand that the radiation from smoke is directly to the lungs and is not a whole body absorbed dose.

Follow-up Question:

Thanks so much for the answer. I am still confused about the radiation doses from cigarettes. Some information says that a heavy smoker gets up to 50 mSv per year while the response to Question 8521 on the Health Physics Society (HPS) website gives very different numbers.

"At one pack of 20 cigarettes a day, the annual effective dose would be 0.36 mSv.”

This number is very low compared to the 50 mSv per year that other sites mention. Am I getting something wrong?

A

Thank you for your question regarding radiation dose and risk. As professionals in the field, members of the Health Physics Society are very attuned to all types of radiation exposure and wish to optimize the benefits of its uses while minimizing any associated risk.

Before answering your question, I would first like to congratulate you on taking perhaps the most important step you could take in improving your health—and that is to stop smoking. The inhalation of tobacco smoke not only contributes to radiation doses to the lung, it also includes a wide variety of chemical toxins and carcinogens—so, from a public health perspective, you have taken the most significant step you can take in protecting and promoting your personal health.

With regard to your specific question, I do not know if internal doses (such as from tobacco smoke) and external doses (such as from CT scans) were summed to reach the noted 100 mSv number. But to put the number in perspective, if you take your 20 mSv CT dose over 15 years, that’s 1.3 mSv per year, plus 400 mSv divided by 14 years of smoking, that is 28.6 mSv, producing a total estimated annual dose of just under 30 mSv y-1. So your annual dose is more than one-third below the stated 100 mSv number.

In addition to the tremendous step you've taken in eliminating smoking, my suggestion would be to make sure you have a discussion with your health care provider about the need and benefit of any x-ray or CT scans. You certainly want the diagnostic benefit of the scans when indicated, but you would certainly want to reduce the number to those only absolutely necessary.

I hope this response if helpful for you.

To your health!

Robert Emery, DrPH, CHP, CIH, CBSP, CSP, CHMM, CPP, ARM
Professor of Occupational Health

Editor's Note: Dr. Emery's answer assumes that the doses you provided are all effective doses. The unit mSv can also be used for equivalent dose which is not the same. Equivalent doses cannot be added; they must be converted to equivalent doses first.

Follow-up Answer:

The reason for the discrepancy is that more recent studies have refined the radiation dose from cigarette smoke considerably. In 1987, the National Council on Radiation Protection and Measurements (NCRP) issued Report No. 95, Radiation Exposure of the U.S. Population from Consumer Products and Miscellaneous Sources, in which it calculated the average smoker's effective dose at about 13 mSv. Even then, the NCRP was uncomfortable with the validity of assumptions used to make the calculation, stating, "For this reason, the NCRP prefers, at this time, not to attempt to estimate an effective dose equivalent for the exposures associated with the use of tobacco products." In 2009, the NCRP issued Report No. 160, Ionizing Radiation Exposure of the Population of the United States, from which the response to Ask the Experts Question No. 8521 was based.

Your total effective dose from 14 years of smoking ~5 cigarettes a day would be around 1.3 mSv.

Kent Lambert, CHP

Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
Answer posted on 12 January 2015. The information posted on this web page is intended as general reference information only. Specific facts and circumstances may affect the applicability of concepts, materials, and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice. To the best of our knowledge, answers are correct at the time they are posted. Be advised that over time, requirements could change, new data could be made available, and Internet links could change, affecting the correctness of the answers. Answers are the professional opinions of the expert responding to each question; they do not necessarily represent the position of the Health Physics Society.