Answer to Question #11294 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 am a 28-year-old male. During the past two years I had tests due to health problems related to my stomach. During this two-year period, the tests I underwent were five chest x rays, one abdomen x ray, one full-body computerized tomography (CT) scan, one barium swallow/meal exam, and one gastric emptying test. I also traveled to and from Japan four times during this period.

I read that cancer risk under 100 millisieverts (mSv) is either nonexistent or too small to observe. However, I am now concerned since the amount of radiation I received during that time from background added to the medical exams and the flying must be well over 100 mSv.

I was very weak and dangerously underweight (38 kilograms [kg]) at the time of the exams. I fear that this condition made me more susceptible to cellular changes as I lacked the proper nutrition to repair damage from the radiation exposure. Something that the radiologist said also disturbs me. He asked me how many x rays I'd had. When I replied six, he said, "Well, now you have had 256."

Could you offer me some advice on my level of risk and how it might affect my future?

A

You have some good questions that are detailed and well thought-out. You should not waste another moment worrying about your risks from the radiation you received. This is especially true since you gained medical and personal benefits from your examinations and flights.

Medical
Each patient's exposure to radiation for a given medical exam is based on patient size, equipment used, and time of exposure. Because of your low weight, the amount of radiation used to acquire the necessary medical images may be far less than average doses.

The average effective doses (in mSv) for the examinations you received are as follows (Mettler et al. 2008):

5 chest x rays = 0.5 mSv
1 abdomen x ray = 0.6 mSv
1 full-body CT scan = 10.0 mSv
1 barium swallow/meal = 6.0 mSv
1 gastric emptying test = 0.4 mSv
 
The average total radiation dose for the medical exams is 17.5 mSv, but your total dose was probably less.

Air Flight
In-flight radiation doses are a complex function of duration of the flight, latitude, and altitude. For example, for a commercial airline flight from New York to Tokyo, the dose rate is about 0.0055 mSv h-1 (Health Physics Society website). The flight time from New York to Tokyo is about 14 hours. So eight one-way trips × 14 hours for each trip × 0.0055 mSv h-1 = 0.6 mSv.

Total
The total radiation dose for the medical and flights combined is probably less than 18 mSv. For comparison, your natural background lifetime exposure is about 3 mSv y-1 × 28 y = 84 mSv.

The Health Physics Society's position statement Radiation Risk in Perspective states that "below levels of about 100 mSv above background from all sources combined, the observed radiation effects in people are not statistically different from zero." In other words, the risk, if it exists, is too small to be seen.

You probably received less than 18 mSv from your listed medical exams and flights, which is a very low dose. Low enough, in fact, that we cannot offer an individual dose assessment.

John P. Hageman, MS, CHP

Reference
Mettler FA, Huda W, Yoshizumi TT, Mahesh M. Effective doses in radiology and diagnostic nuclear medicine: A catalog. Radiology 248(1): 254–63; 2008.

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 28 August 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.