The attached link is to an article questioning whether CT Scans cause cancer. There is no safe level of ionizing radiation and the article estimates how many cancers might be caused by medical exposure to ionizing radiation including CT Scans. The Radiological Society of North America says that the average exposure of Americans to natural background radiation (NBR) is 3 mSv per year. This number is incorrect however since it includes all exposures including medical, industrial and flying. The actual figure for NBR, not including man-made radiation is approximately 0.87 mSv per year.
https://www.healthdigest.com/954539/could-ct-scans-cause-cancer/