Answer to Question #10528 Submitted to "Ask the Experts"
The following question was answered by an expert in the appropriate field:
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?
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