From Tidal Pool Software:
X-rays, CAT scans, fluoroscopy (including angiography/angioplasty), and nuclear medicine exams all cause ionizing radiation to be delivered to the body, which can cause cancer. Over the last 15 years, the use of medical imaging has been rapidly increasing. There have been recent estimates that up to 1.5-2% of all cancers within the US are caused by radiation from CAT (CT) scans.
The purpose of Radiation Passport is to educate about the radiation and cancer risks associated with medical imaging exams and procedures that physicians (and dentists) want you to undergo, to keep track of radiology and imaging-related exams and procedures, and to provide an estimate of risk of developing cancer because of this radiation.
The radiation exposure and associated risk numbers are based on published scientific journal papers, however, are in each case an estimate. There are different methods by which to estimate the associated risk.