What is the maximum number of times a person can safely undergo x-ray scanning? If this limit is exceeded, are there serious and/or life threatening side effects that the person may experience?
A person should undergo Xrays as often an they are necessary, because the risk-to-benefit ratio is usually very far in favor of the benefit.
As an example of this idea of risk-to-benefit ratio, lets take getting into a car.
There is always a risk to getting into a car. After all, they move quickly, slide on slippery roads, and hurl towards (and potentially at) each other at a frightening rate of speed. You probably know someone who died in a car accident. Yet, probably without giving it a single thought - except when you're buckling your seat belt - you get into a car several times per day/week. Because the benefit (distance transportation, convenience) is higher than the risk of injury in a motor vehicle accident (this example is actually flawed, but we'll ignore that for the moment.)
Similarly, there is always a risk to getting an xray, but sometimes you just have to get them. The risk is low compared to the benefit. You wouldn't want anyone putting you in a cast without knowing what kind of bone fracture you had, because some kinds need to be casted differently, some need to be casted longer, some need operative repair, and some only need a splint. The benefit outweighs the risk.
There is no completely safe lower limit of radiation. Radiation (especially in fetuses and children) increases the likelihood of cancer. Our information comes mostly from atomic bomb survivors, people exposed at Chernobyl (nuclear reactor accidents), people treated with high doses of radiation for cancer and other conditions, and people exposed to high levels of background radiation, e.g. uranium miners.
Radiation doses are measured in millisieverts (mSv). For comparison's sake, you should know that, depending on where you live,
- natural background radiation exposure accounts for an average of 3.1 mSv/yr
- A seven hour airplane trip exposes you to 0.02 mSv of radiation per trip
- Backscatter Wave Scanners in airports exposure is just less than 0.0001 mSv per scan (so one average year exposes you to 31,000 times as much radiation as an airport scanner.)
- a four bite-wing dental series is about 0.005 mSv
- a two view Chest X Ray doses you 0.1 mSv
- your average CT scan is going to give you 7 mSv of exposure
Is that safe? What is your chance of getting a lethal cancer from that? The answer is: no one knows. It depends on a lot of unmeasurable things: genetics, your age, your ability to repair the damage, which area of the body is being dosed, whether there are other carcinogens at work (e.g. viruses or co-carcinogens), etc.
The following all give you a (estimated) 1 in a million chance of dying from that event:
- Smoking 1.4 cigarettes (lung cancer)
- Eating 40 tablespoons of peanut butter
- Spending 2 days in New York City (air pollution)
- Driving 40 miles in a car (accident)
- Flying 2500 miles in a jet (accident)
- Canoeing for 6 minutes
- Receiving 10 mrem (.1 mSv) of radiation (cancer)
So, you can estimate that (maybe) the risk of dying from a 7 mSv CT scan is about equivalent to driving 2800 miles.
What is the maximum number of times a person can undergo x-ray scanning?
As often as necessary. As long as the benefit outweighs the risk.
Is their a maximum limit? If so, what are the side effects that the person will be subjected to if he undergoes x-ray scanning more number of times?
No, there's no maximum limit. The risk is cancer. The risk is low, but not negligible. It doesn't go up linearly with every Xray study you have.
Are they life threatening and do they have long term effects on the body of the person?
Yes; cancers are often life threatening.
What can you do about it?
- Don't ask your doctor for an unnecessary Xray.
- Ask your doctor if an Xray they ordered is necessary (sometimes they are ordered to reassure the patient - or their parents, in the case of head injury - that nothing is wrong.) A doctor worth their salt will respect you for asking. Sometimes it's ok to take a "wait-and-see" approach. Sprained ankles meeting certain criteria never need an Xray. It's ok to ask. _ If your doctor orders a CT scan of something, ask if an MRI would be better. (They cost more, and are sometimes as good or better than a CT scan.)
- wear a shield when offered (will shield the parts of your body they don't need to see.
- ask about the age of the machine (newer machines often use lower dosages than older ones (post 2005 is better).