Radiation in CT scans, x-ray/radiographies and PET scans (III): what to do if my doctor recommends one

This is the last of a series of 3 posts describing:

1. The value and cost/harm of medical tests involving radiation, purely from a scientific perspective.
2. Other factors affecting the prescription of these tests.
3. What to do if a doctor recommends such a test. This post.

CT/PET scans are a good thing, when they are necessary. So, the key is to find out if they are really necessary FOR THE PATIENT (not for the doctor). Without intending to give any kind of medical advice or advice on how you should talk to your doctor (disclaimer!!) these are some of the things I would keep in mind:

1. Tell the doctor if you took any other CT previously. They may be able to reuse those.
2. Ask to explain the risks of not taking the CT.
3. If they ask for a CT with contrast, ask them if they can make first the one without and based on the result, think of doing the one with contrast, or viceversa. Basically, the contrast CT is a full new scan, doubling the radiation...
4. Ask why the doctor is recommending this test given ALL the symptoms. It should NOT be prescribed as a routine or screening test (unless that is what you want... like some asymptomatic people will do a full body scan "just in case").
5. Ask them to do all other less harming tests before this one, if there is no emergency/rush. For instance, an MRI is usually a good replacement (watch out with the argument that it is not, more on that below). Also, you could have the possibility of treating the first suspect illness and see what happens. If symptoms persist, then you may have to move to a CT (or MRI...).
6. You may want to ask for a second opinion. People may not think of that for a CT, but would you do it if they recommend opening you to check if something is wrong inside you? Yes, looks that the two are not comparable, but go through your numbers, check the increased probability of inducing a cancer and then decide if a 2nd opinion is worth...
7. As explained, other kind of scans, like x-ray or mammograms do have much lower levels of radiation. Concerns arise by the cumulative effects of these over the years, specially when used as prevention. These are certainly harder to discern but I would look at policies, not only local but foreign. For instance, it is common practice to have dental x-rays done yearly in US, as insurance covers it, but is it something that you really need, even if free? A US dentist may say so, but somehow, in Europe, this is not done at all.
8. If you got the time, take your time on the discussion. You are the one about to get radiated! And leave few days after the talk to think about, research, consider alternatives, etc... For instance, you may want to check into alternative tests, like the possibility of using an MRI.

Please, read this with common sense. You should not delay the diagnosis of a life threatening condition for a one in a thousand probability of inducing a cancer. Also, if you have been diagnosed with cancer, something like a PET to find secondary sites of a metastasis may well justify the much smaller risk of a future cancer. Nevertheless, if you reach the hospital with all the symptoms of a kidney stone and a previous history of kidney stones, you may want to waive the CT scan that most of US hospitals ERs will suggest doing and see how you feel next day... Bottom line, as I started, imaging tests involving radiation are very useful tools and there are many doctors out there using them in the benefit of patients, but there are many too being prescribed routinely, defensively, or out of ignorance...

Good luck and I hope the posts were helpful