Worried about radiation from scans

[Hansencat]

Hi, hoping someone can help with this? In February I had a full body CT followed up 4 months later with an abdomen/pelvis CT to check on some findings from the first one. Told everything ok but now I've been referred for a PET CT. (Have quite a complicated health thing going on).

I'm really worried about the amount of radiation I'm having in a short period of time. Doctor couldn't answer my questions about it, just said I shouldn't worry about totting up my exposure - but I am worried! Also had an abdominal Ct and a nuclear bone scan 8 years ago so feel I've had a significant amount of radiation.

Does anyone know how much radiation is in these scans? Does having contrast make it much worse? Is it usual to have a PET scan after a clear CT?

If there are any radiographers out there who can help I'd really appreciate it. Thank you.

To answer your questions:

1. The amount of radiation in a full body CT (I assume you mean and chest, abdomen and pelvis) is 10 mSv, a CT abdomen/pelvis is 7 mSv and a PET is 20 mSv. Your background radiation is about 3 mSv depending on where you live (higher in Cornwall, for example). So your total radiation from the two CTs and the PET is the equivalent about 12 years of background radiation. These numbers will vary depending on a lot of factors so this is just a ballpark figure.
2. A bone scan (DEXA for osteoporosis) is only 0.001 mSv.
3. Having contrast (for the body CT) doesn't make the radiation any higher unless they scan you multiple times during the same study.
4. If you had the abdominal CT and nuclear bone scan 8 years ago that radiation risk doesn't really count anymore. A lot of the danger comes from how much radiation you receive in a single dose or very close together (e.g. within a week).
5. It is usual to have a PET after a clear CT, they detect different things. Sometimes a CT can look normal or there will be something on the CT we're not sure if it's normal or not. A PET can be helpful in finding very small abnormalities or clarifying whether something is normal or not. Similarly, having a follow-up CT is helpful to see if there's been any change in something that may or may not be normal picked up on the first scan.
6. Every decision is based on the risk vs benefit. I assume you needed these scans and the danger of not having them and missing something serious is much higher than the risk of radiation. Bear in mind some patients will have multiple CTs (e.g. cancer follow up) but the risk of missing worsening disease is much much higher than the risk of radiation. Also, our scanning techniques have developed much further as have the safety controls around radiation exposure.

Let me know if you have any further questions.

Source: I'm a radiology doctor

Hello, thank you so much for responding and giving me such a comprehensive answer.

Regarding my question about contrast - I seem to remember it being injected part way through the process. Does this suggest I was scanned more than once?

I have the same anxiety @Hansencat . @SA379 You mention danger relating to how close the scans were to each other - I had 2 emergency pelvic/abdominal CTs with isolation 4 days apart due to appendicitis. I didn't know what a CT scan was and now I'm scared that I may have hurt myself or future children; my grandmother died of ovarian cancer after a hysterectomy. I haven't had other scans beyons routine X-rays years apart.

Your risk is very low still. It’s not zero as there is always a risk with radiation exposure but, as mentioned above, the risk of missing appendicitis is much much higher than that of the radiation exposure. There are many people who have multiple CT scans and haven’t developed cancer.

@SA379 Thank you so much for replying to me, and so quickly! I've been doom Googling since the scans and so much of what I read is scary. I really appreciate the reassurance!

No worries. I think often these things are taken out of context. We try to not expose people to radiation unless absolutely necessary. Your exposure was equivalent to about 7 years of background radiation or 7 transatlantic flights. If they had missed an appendicitis that then burst that is an emergency with a risk of sepsis and death, but they wouldn’t just go in and operate without confirmation because of the risk of surgery so the CTs were necessary.

Hope it’s okay to jump on this thread. I’ve been worrying about a similar thing but with MRIs as had to have a couple bar close together. Is it the same kind of thing @SA379 ? Thanks so much for any info you can give.

There’s no radiation risk with MRIs as they use magnets, not radiation, to take images. Any danger would be if you had a pacemaker or metalwork but they check for these before you have the scan. Very safe imaging technique.

Thanks so much, really appreciate it.