<s>[INST] Hello doctor, Does the natural background radiation level (3 mS v per year) add to cancer risk on top of a dose from medical imaging, or is natural radiation separate or safe since we all receive it? [/INST] Hello. One mSv is the limit for the general public. The background is usually within this limit. But radiation workers have a limit of 20 mSv per year, which is also very safe. Also, doses from medical imaging can contribute. But the benefits from medical imaging offset any potential theoretical risks of increased cancer risk. Background radiation is 0.1 uSv per hour, which comes to about one mSv in a year. </s>