Answer to Question #10528 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

My 11-year-old daughter received a bone scan followed by a skeletal survey, CT (computerized tomography), and CT-guided biopsy. I was given the following information about the radiation doses she received:

Skeletal survey—0.8 mSv
CT lumbar sacral spine—0.7 mSv
CT biopsy—3.1 mSv
Bone scan—5.3 mSv

Total Effective Dose—9.9 mSv

I read a lot about risk from CT scans, but not bone scans. What can I understand from the above calculation? Is CT more dangerous because it is done to one part of the body and not the whole body? Is this amount of radiation dangerous for an 11-year-old girl?

A

Effective dose takes into account that only a part of the body receives the radiation dose and that different parts of the body have different sensitivities to radiation. This allows an "apples to apples" comparison. So a 4 mSv dose from a bone scan and a 4 mSv dose from a CT scan carry the same risk. It also allows you to add the doses together. 

From the Health Physics Society’s position statement on radiation risk, "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. The approximately 10 mSv received by your daughter is well below this.

It is also important to remember that your daughter benefited from these procedures and the benefits no doubt significantly outweighed the risks.

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 30 January 2013. 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.