Answer to Question #10788 Submitted to "Ask the Experts"
The following question was answered by an expert in the appropriate field:
I used an x-ray risk calculator to calculate my radiation dose. According to the calculation, in the year 2010 I received 1 mSv over background due to three chest x rays and several long distance flights. In the comparison section, the calculator stated that pilots and other flying crew receive about 2.2 mSv of additional radiation per year. I have two questions and I would really appreciate your expert answer.
- Is it the same if a person receives 1 mSv of radiation all at once (e.g., from a single x-ray session) and if 1 mSv is accumulated continuously over a period of one year. That is, can we really compare radiation received by pilots over a year and a diagnostic x ray?
- Based on my online investigation, the amount of radiation received from a single chest x ray is between 0.01 mSv and 0.2 mSv. That is a quite big difference; for my chest x-ray calculations I used 0.233 mSv. Am I overestimating the dose?
Your question centers on the issue of the risk associated with a single exposure resulting in a certain dose as compared to several multiple exposures resulting in the same cumulative dose. The term used for this concept is “fractionation.” When doses are fractionated, this allows for cellular repair to occur if cell damage is actually incurred. So philosophically, the fractionated dose would result in a lower risk than an acute dose. But it is important to keep in mind that the risk associated with a dose in the ranges you mention (1 mSv to 2.2 mSv) is miniscule compared to many other risks individuals encounter every day. For example, the average American receives an annual dose of 6.2 mSv each year from man-made and natural sources of radiation.
The dose delivered from x rays can vary because of the technique that is used to make the image. The technique used is driven by many parameters such as the angle of the image, the sensitivity of the image receptor, the number of projections, and the size of the patient. Using 0.233 mSv would be on the high side of the normal range of effective dose for chest x rays but there is little if any risk associated with a radiation dose of this magnitude.
Robert Emery, DrPH, CHP, CIH, CBSP, CSP, CHMM, CPP, ARM
Professor of Occupational Health