The dangerous radiation

Most of the dangerous radiation is radiation that we can't see. For instance, at any point in time, we are constantly being bombarded by cosmic radiation that originates from other space. Another type of radiation exposure comes from dental and medical procedures (e.g. chest x-rays, CT scans, PET scans, etc). Radiation exposure can also occur during therapeutic procedures such as during the treatment of cancer.
Should you be concerned when you received a dental x-ray or CT scan? Why or why not? Consider the risks and benefits, as well as the doses of radiation involved