Recently, there has been much talk in the media about the risk of developing cancer due to radiation exposure from radiology tests, such as CT scans. While there have not been studies following people over time to assess for cancer risk, there are plenty of studies on the amount of radiation received in these tests and a model (called BEIR VII) that calculates how that may translate into increased cancer risk.
So, how many tests is too many? Here is where it gets sticky. The amount of radiation from one scan can vary dramatically from machine to machine, even within one institution, depending on the radiologists' protocol, whether repeat pictures are taken of an area for clarity, etc. Different scans have different levels of radiation; for example, a CT scan exposes you to much less radiation than an angiogram of the arteries in your heart. What it comes down to is a discussion between you and your healthcare provider when a scan is ordered. Is this test necessary? What will we learn from it and will this change our treatment plan? Weigh the risks and benefits and make an informed decision with each test.