Answer to Question #12437 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:


I have had multiple medical procedures involving radiation. They included an esophagram, mammogram and single-view chest x ray in 2012, a two-view chest x ray and a chest and sinus computed tomography (CT) in 2016. I estimate my overall dose at less than 9 millisievert (9 mSv). My questions are (1) is getting radiation multiple times worse than one large exposure, and (2) can you compare a year's worth of radiation spread out over a year to that radiation coming all at once?


At low radiation doses such as those from diagnostic imaging studies, the time frame is of no consequence. At very high radiation doses, such as those used in radiation therapy to treat cancer, the time frame is of significant consequence and is factored into the treatment plan. A single large dose (much larger than you received) can be much more damaging than the same dose spread out over a long period of time. This is why in radiation therapy, the patient receives a fraction of the total treatment dose each day for a period of time (often weeks). 

At effective doses below 100 mSv (and you received less than 9 mSv according to your calculations), the risk, if it exists, is too small to be observed. At effective doses higher than 100 mSv in a population, the number of cancers in that population might increase above the normal incidence rate. In other words, if everyone in a population of 1,000 people received more than 100 mSv, the number of cancers in that group might be slightly higher than in 1000 people that receive less than 100 mSv. 

For your situation, the time frame of radiation exposure is of no consequence.

Kent Lambert
Certified Health Physicist
Fellow, Health Physics Society

Answer posted on 6 July 2018. 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.