Answer to Question #12342 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 recently asked a question about how many mSv I received from a chest computed tomography (CT) scan and a barium swallow. The total was around 7.5 mSv for both procedures.

At how many mSv do cells start to die? Under what mSv can the cells repair themselves? I understand that a chest x ray is much less radiation than a CT scan, but do our bodies repair themselves the same way compared to a large or small dose? Do cells immediately begin repair right after exposure or is it an ongoing mechanism?

I did read that some scientists believe that some radiation boosts immunity and possibly protecting us from radiation harming us in the future. How true is this?


Cells are constantly dying and being replaced. It's an issue when they die faster than they can be replaced. A CT scan results in low doses, a chest x ray in lower doses. Radiation therapy for cancer treatment results in high doses. It takes radiation therapy type doses to kill cells faster than they can be replaced. It's not an issue with radiation exposures from diagnostic imaging.

Cells, or more specifically, DNA molecules in cells, are constantly being damaged and repaired. This happens all the time, every second of every day, in every cell in the body.

While some studies have shown positive health effects from low-dose radiation, at low doses the epidemiological evidence is not consistent.

Thank you for using the Health Physics Society's ATE feature.

Kent Lambert, CHP, FHPS

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 7 May 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.