In this thread on getting two x-ray scans in rapid succession, I included a table that provides the radiation dose or exposure from a variety of common tests. Since that thread seems to have run its course, and since there might be a more general interest in the table, I am re-posting it here for everyone’s interest and reference.
Note that a CT of the chest gives the equivalent exposure as about 400 chest x-rays or almost four years of natural background radiation - impressive figures, but still considered safe.
Diagnostic Typical effective Equiv. no. of Approx. equiv. period
procedure dose (mSv) chest x-rays of natural background
single arm, leg, hand, or foot
less than 0.01 less than 0.5 less than 1.5 days
(single PA film)
0.02 1 3 days
0.06 3 9 days
0.07 35 4 months
1.0 50 5 months
0.4 20 2 months
0.7 35 4 months
0.7 35 4 months
2.4 120 14 months
1.5 75 8 months
2.6 130 15 months
3 150 16 months
7.2 360 3.2 years
2.0 100 10 months
8 400 3.6 years
CT abdomen or pelvis
10 500 4.5 years
I don’t have a table that correlates the therapeutic radiation doses with numbers of chest x-rays or equivalent natural background radiation exposure, but you can convert if you like easily enough. 1 Gy of radiation dose is about equal to 1 Sv (Sievert) for all therapeutic radiations except those rare instances where neutron radiation or proton radiation are used. The table you have shown here estimates radiation dose from a chest x-ray at 0.02 mSv or 2 x 10exp-5 Sv, and says that that is the equivalent of 3 days of natural background radiation exposure. Natural background radiation levels vary so much around the world that I’m not sure how meaningful that second correlation is, but let’s go with it for now.
Curative intent radiation treatment for most cancers requires at least 60 Gy, and often higher. Highest doses used are usually with prostate cancer and some of the gynecological cancers, like vaginal or cervix. There are exceptions: more radiation-sensitive tumours like lymphoma or seminoma usually being treated with 30 - 35 Gy, or small cell lung cancer being treated with 45 - 50 Gy. So, a 60 Gy course of therapeutic radiation is (in terms of dose) the equivalent of giving somebody 3 million chest x-rays or 1 million days (or about 2 740 years) of natural background radiation. (I hope I’ve done the math correctly…) This sounds appallingly high, but remember that a 1 cm tumour is supposed to have 10exp9 cells in it, some proportion of which are the clonogenic cells and others of which are cells that can be recruited into becoming dividing cells (typical growth fraction for a typical human tumour usually quoted as 40%), and most of the tumours we treat are unfortunately much larger than 1 cm and so have even more evil cells to kill off…
Palliative radiation doses are typically lower ( 20 - 30 Gy commonly) but similarly on a total order of radiation dose higher than diagnostic radiation doses.
How much radiation is considered too much radiation for the human body? I’m talking about controlled radiation from medical tests. I’ve had two courses of radiation for Hodgkin’s Disease, once over most of my chest, and once mostly contained to my abdomen near my stomach. Plus I’ve had the usual plethora of chest xrays, CAT and PET scans that go along with a chronic disease for three to four years.
How concerned should I be about additional exposure to radiation?
Well the LD 50/30 dose for ionizing radiation is 400 to 450 rem (4 to 5 sieverts), according to the NRC’s site(though I used to hear 500 rem when I was in school).
Everyone should be concerned about radiation exposure at some level, but the way we think about radiation exposure in the medical field is about weighing it as a risk compared to the benefit of the diagnostic study or therapy. So, is your quality of life more likely to be increased by taking the risk of the procedure? Pretty much, in all medical cases, yes. There has been some frivolous use here and there, but most physicians are moral.
I’ve been an x-ray tech for 15 years and a nuclear medicine tech for 12 years BTW.
Our bodies have systems to repair damage done from radiation exposure. With relatively low radiation exposures, such as those from diagnostic tests, and hopefully reasonably long intervals between those exposures, there is no realistic need to worry about the radiation exposure from the tests. You are weighing off the risks of a little radiation dose from tests every few months or so versus the risks of not looking for evidence of your Hodgkin’s Disease coming back (for example, missing a treatable recurrence while it is small/localized). I can’t think of any situation offhand where I would recommend against the diagnostic radiology tests based on previous diagnostic radiation exposure only.
From a point of view of the therapeutic radiation doses, like the courses of radiation for HD that you had: every part of the body has a different limit to how much radiation it can tolerate. The previous dose you had, how long ago you had the dose, how well you healed up after the courses of radiation, and what organs received what dose (relative to what they can tolerate) - all of these factors will affect whether further therapeutic radiation doses can be given to a previously treated area, if that were to be needed. Your risks related to radiation exposure are significantly higher from the radiation used for treatment than from the radiation used to see what’s happening inside your body, just because the dose of radiation from the radiation therapy is so much higher. Hopefully those risks were explained to you before you went ahead with the treatment.
Just to clarify, although the linked site does reference this: the LD 50/30 applies only for acute (“one-off”) radiation exposures to the total body all at once, as opposed to Goblinboy’s situation of smaller repeated exposures to parts of his body. The whole body tolerance to radiation is much lower than that for just parts of the body receiving radiation. Also, giving a radiation dose over a long period of time (as opposed to all-at-once) really increases the body’s ability to handle the radiation dose by a lot. Where 50% of people would be dead in 30 days with a 4 - 5 SV or Gy dose if they got that to their whole body all at once, we routinely treat parts of patients’ bodies to 60 Gy or more using Mon-Fri treatments over 6 or more weeks without any risk of killing them from the treatment.
I’m not sure if these responses are what I want to hear or not!
But yeah, I understand and accept the possible risk involved with radiation treatment over the guaranteed risk of letting the cancer grow. Am I right in thinking though, that if you go long enough without developing cancer or some other abnormality from the radiation, the danger of additional problems dissipates? I have scarring in my lungs that is thought to be from the radiation treatments. But I don’t have cancer, so it was a bit of a tradeoff.
Just to clarify and put a fine point on it, radiation exposure for cancer treatment involves focused radiation on a well-defined, three-dimensional volume within the body, outside of which the dose is much lower. Compare this to radiological exams (i.e. X-rays) where significant parts of the whole body are exposed to unfocused radiation. Whole-body exposure, as already pointed out, is a very different scenario than therapeutic radiation, and is in general what industrial exposure guidelines are founded on.
In general, yes. I can’t give you an unqualified yes because there are some late effects of radiation for which your risk increases with time, and others for which (while the peak period of risk has passed) the risk never drops down to zero.