Does Radiation from X-Rays/CT Stay in Body Forever (Risks)?

[kyphysics]

I'm slightly confused by what medical professionals/scientists say when they say to limit exposure to x-rays/CT/PET, etc. scans if possible, due to radiation. I'm also confused as to why we're often told to leave the room when a relative is getting such a scan, given that medical staff that administer them are there all day as part of their job (presumably 40 hours a week), b/c of radiation exposure (would a few seconds really be as bad as the person working there who puts up with this constantly)?

Curious about the following (that I haven't found via Googling):
i.) When you get such a scan (x-ray/CT/PET/mammogram, etc.), is the brief seconds or minutes of radiation exposure something that stays in the body forever (until you die)? I know the radiation exposure, itself, obviously only lasts a few seconds or minutes as they do the imaging. Afterwards, there is no more radiation in the room. But, if it's now been absorbed by the body (is that what happens?), then is it still there "radiating" (or does it stop?) forever? If not, how long is the radiation in the body gone? And, if it leaves, how long might the negative effects (if any) last?

ii.) Why can't a family member just stand far away from the person getting scanned the way medical staff do to protect themselves from radiation during a scan? Or, are those areas still not safe and you (and staff) can get radiation still?

 

[.Scott]

Let's do one type of radiation at a time:

x-ray, CT, mammogram: These are all x-rays. The staff will follow practices to keep themselves shielded. They may commonly use lead-lined aprons and will often operate the xray device from another room or around the corner from the device. They need to keep themselves shielded. Vistors are simply kept out because they are not trained to leave on cue. The x-rays do not stay in your body. They leave instantly. But they can leave damage behind - damaged DNA or trace amounts of highly activated chemicals. So it's important to limit the dose.

PET scan: There are several medical imaging techniques that involve injecting tracers into your body. The tracer is radioactive. So limiting the dose is important.

You didn't mention MRI, but let's cover that one: This is magnetics and microwave radiation. It is non-ionizing, so dose is not so important. If they do not allow visitors, it will be because of the very high magnetic fields - easily powerful enough to turn any mislaid steel object into a deadly projectile when the MRI powers up.

 

[kyphysics]

The x-rays do not stay in your body. They leave instantly. But they can leave damage behind - damaged DNA or trace amounts of highly activated chemicals. So it's important to limit the dose.

Thanks for the breakdown and clarifications. In terms of "highly activated chemicals" being left behind, are those cancerous and, if so, how long do they stay in the body?

If they do stay, is that why they say the cumulative effects of lots of lots of scans can cause cancer? I know one CT scan isn't very dangerous. But, medical professionals do say, if possible, to limit the total number of scans, b/c over the course of a lifetime, they can lead to something like cancer.

 

[JT Smith]

It's cumulative exposure that matters. At least that's what is understood. Think of it like crossing the street. There's a chance you could be hit by a car. A quiet street might be like a dental x-ray: you'd need a lot of those crossings to feel like you were taking on significant risk. A CT scan would be more like a busy multi-lane road. Do that often enough you could be in trouble.

If you know how to use an internet search engine (it's worth learning how) you'll be able to quickly pull up charts that list the dose levels of various EM radiation sources. Try searching "banana equivalent dose". Eating one banana exposes you to a small but measurable amount of radiation. A dental x-ray exposes to you roughly the same radiation as eating 50 bananas. An LA to NY airplane flight is equal to about 400 bananas. And a full body CT scan is over 100,000 bananas worth.

Risk of getting cancer is small with any of those by itself. But keep adding them up and your risk goes up. Just like so many things.

 

[.Scott]

If they do stay, is that why they say the cumulative effects of lots of lots of scans can cause cancer? I know one CT scan isn't very dangerous. But, medical professionals do say, if possible, to limit the total number of scans, b/c over the course of a lifetime, they can lead to something like cancer.

Just to be clear, we are talking about the long term effects of exposure to ionizing radiation. We are talking about exposure to medical procedures and typical environmental exposure. We are not talking about the kind of intense "acute" exposure that will prompt radiation poisoning and death in a matter of hours.

For many poisons, there is a "safe dose". As an extreme example, there is such a thing as "water intoxication". Drink enough water and and your cells will swell up - perhaps lethally. But drinking normally is not just harmless, it's essential.

A strong argument can be made that, except for acute radiation poisoning, ionizing radiation does not follow that pattern. As best anyone knows, a single unlucky photon is able to directly or indirectly break a DNA molecule in a way that, in time, allows its cell to be the start of a cancerous growth.

So what can accumulate is risk. If you are lucky, an exposure to ionizing radiation (either naturally or from an medical procedure) will not create anything that can promote cancer. But you don't want to take that risk more often than you need to. Eventually, the odds could catch up to you.

But let me attempt to answer your question a bit more directly. Most DNA damage is not cancerous - it may have a benign effect on the cell or just out-rightly kill it. If it does make the cell cancerous, your immune system might recognize it and destroy that cell. In the most unlucky case, the damage reprograms the cell to grow unchecked but to do it in a way that doesn't trip your immune system.
Now that you have a notion of the process, you may ask what is the timeline for this process. The best answer I can find is from an article from the "Health Physics Society" website "Radiation Answers" which starts by saying:

This discussion isn’t as easy as being able to say “here’s a dose and here’s the effect of that dose.” Our current medical knowledge does not allow us to identify what causes a cancer, so a radiation-induced cancer doesn’t look any different than the same cancer caused by other possible agents. We do know that radiation-induced cancers do not appear until at least 10 years after exposure (for tumors) or 2 years after exposure (for leukemia). This time after exposure to possible cancer formation is called the “latent period.” The risk of cancer after exposure can extend beyond this latent period for the rest of your life for tumors or about 30 years for leukemia.

 

[kyphysics]

Just to be clear, we are talking about the long term effects of exposure to ionizing radiation. We are talking about exposure to medical procedures and typical environmental exposure. We are not talking about the kind of intense "acute" exposure that will prompt radiation poisoning and death in a matter of hours.

I mostly assumed that. I've never heard of someone getting cancer immediately after a scan and then dying from it.

As best anyone knows, a single unlucky photon is able to directly or indirectly break a DNA molecule in a way that, in time, allows its cell to be the start of a cancerous growth.

So what can accumulate is risk.

Your wording here was slightly confusing. You seem to imply that any one scan can cause cancer as a photon may damage a DNA molecule during it.

Then you say it is mostly about cumulative risk. I can see how both could be true - e.g., if it is very rare for a photon to damage a DNA molecule in a way that would cause cancer AND that if you give it enough "tries," then over time (the cumulative aspect) the chances of that happening increase. Is that how you meant it?

In other words, in theory, is it that you can get damaged cancer-causing DNA the first scan you get (and, thus, cancer immediately???), but that for most people it tends to only happen after many, many years and many scans? Or, is that not really possible at all and you meant something else?

 

[kyphysics]

This discussion isn’t as easy as being able to say “here’s a dose and here’s the effect of that dose.” Our current medical knowledge does not allow us to identify what causes a cancer, so a radiation-induced cancer doesn’t look any different than the same cancer caused by other possible agents. We do know that radiation-induced cancers do not appear until at least 10 years after exposure (for tumors) or 2 years after exposure (for leukemia). This time after exposure to possible cancer formation is called the “latent period.” The risk of cancer after exposure can extend beyond this latent period for the rest of your life for tumors or about 30 years for leukemia.

This was very interesting. W/r/t the time it takes for cancer to appear after exposure, does that mean a cancer cannot even develop before that time period for some medical/scientific reason? My thoughts keep going back to your photon damaging DNA earlier and it leading to cancerous cells growing/multiplying. Could that not be instantaneous?

Or, does it medically take 10 years for some damaged DNA cell to grow into a tumor (that seems a bit slow)? Or, maybe I'm just reading it wrong. Thanks.

 

[kyphysics]

Btw, I'm asking all these questions, bc my father has gotten about 5 CT scans (1 a PET/CT to be exact) in the last 6 months (he's only had one prior to 2023 about 7 years ago). We get the result of the PET/CT at doctor's consultation this week.

For many personal reasons, it's been nerve-racking. I'm also just genuinely wanting to understand the science better.

 

[.Scott]

Your wording here was slightly confusing. You seem to imply that any one scan can cause cancer has a photo may damage a DNA molecule during it.

Then you say it is mostly about cumulative risk. I can see how both could be true - e.g., if it is very rare for a photo to damage a DNA molecule in a way that would cause cancer AND that if you give it enough "tries," then over time (the cumulative aspect) the chances of that happening increase. Is that how you meant it?

Then you say it is mostly about cumulative risk. I can see how both could be true - e.g., if it is very rare for a photo to damage a DNA molecule in a way that would cause cancer AND that if you give it enough "tries," then over time (the cumulative aspect) the chances of that happening increase. Is that how you meant it?

In other words, in theory, is it that you can get damaged cancer-causing DNA the first scan you get (and, thus, cancer immediately???), but that for most people it tends to only happen after many, many years and many scans? Or, is that not really possible at all and you meant something else?

Yes. I think you basically have it.

Part of the problem is that you are trying to pull more information than science has collected. It took decades before science was able to describe a direct chemical path from tobacco smoking and lung cancer. No one has ever directly observed the entire process of an x-ray photon ultimately killing someone.

But let me describe a plausible example:
An x-ray photon enters your body and strike a salt molecule in the nucleus of one of your cells. In breaks that molecule into a chlorine atom and a sodium atom. The sodium atom interacts with water causing some minor damage, but the chlorine atom then latches onto the side of a DNA molecule causing one of its nucleotides to become non-functional. Ions created from ionizing radiation are very reactive and will not persist in our bodies for long. So at this point, less than a second has elapsed. And since this cell isn't very active, nothing happens for several years. Eventually, the cell depends on that particular damaged DNA code. If it depended on it for some maintenance function, the function would fail and the cell would simply become sick. But for some reason, the cell wants to divide and when it does, the damaged nucleotide will not copy correctly and the new cell suffers some loss of function. If that loss of function didn't relate to the regulation of cell division, the cell would simply be sick. But it does, so it is potentially cancerous. That damaged DNA code corresponds to some protein that the cell is relying on. Since it just separated from another cell, the two may have split the supply of that protein evenly - so the cancer may not be progressing at full pace quite yet.
But after a few years a couple of things happen: First, the cell divides a few more times and the daughter cells are now relatively free of the critical protein. Second, the daughter cells find some way to evade detection by the immune system. Finally, the cancer continues to develop and eventually causes symptoms and a diagnosis.

A less plausible example might involve having the x-ray photon creating a long-lasting carcinogen that eventually causes cancer. But the timeline for carcinogens is generally somewhat longer than it is for ionizing radiation. So, at a minimum, this less plausible example would not apply most of the time.

But in any case, I think I have addressed your question. There is no way of knowing exactly what an xray photon will do. Nearly all of the time, it does nothing important - and there is no actual cumulative effect. But the only way to know is to wait a few decades, so what is important is only the risk because only the risk can be known in timely fashion.

 

[.Scott]

Btw, I'm asking all these questions, bc my father has gotten about 5 CT scans (1 a PET/CT to be exact) in the last 6 months (he's only had one prior to 2023 about 7 years ago). We get the result of the PET/CT at doctor's consultation this week.

For many personal reasons, it's been nerve-racking. I'm also just genuinely wanting to understand the science better.

Doctors and radiologists are very mindful of the expense and health risks of PET and xray scans. So if he's been to radiology 5 times, I am sure it was for very solid reasons that are well worth that expense and risk.
I also think that its useful to compare those risks to situations where people choose risk for less compelling reasons. When he walks in the sun, does he use sunscreen and a visor? If not, both the visible light and the uV are ionizing and the uV is especially able to create cancer and other skin damage.

 

[kyphysics]

Doctors and radiologists are very mindful of the expense and health risks of PET and xray scans. So if he's been to radiology 5 times, I am sure it was for very solid reasons that are well worth that expense and risk.
I also think that its useful to compare those risks to situations where people choose risk for less compelling reasons. When he walks in the sun, does he use sunscreen and a visor? If not, both the visible light and the uV are ionizing and the uV is especially able to create cancer and other skin damage.

I was wrong. It was 11 CTs (b/c I didn't count the 3 in a 24-hour period - I only counted that as 1, nor did I count 3 others, which were full chest/ab).

First 4 CTs were 100% justified, as he had a subarachnoid hemorrhage. That is a life-threatening condition & the bleed and hematoma in the brain can expand. They found the bleed & then had to scan 3 more times to confirm it was controlled (they infused him with all sorts of stuff to help it clot).

PET/CT was 100% justified, as there is a nodule that looks cancerous. Some chest/ab CTs were iffy, b/c he only had surface level skin scrapes when he fell there. He reported no pain and passed various physical tests (like range of motion, squeezing fingers, resisting pressure, etc.).

I wasn't as aware of radiation dangers when this all began, but his primary care doctor expressed strong concern about certain tests (he obv. agreed with the obvious ones, but some of the iffy ones he said he was surprised by). I WONDER if the E.R. doctors look at how many scans a person has had in a short period of time before they do another one???? Seriously, they may just be looking at current situation and thinking a single CT won't hurt. Hard to tell.

I asked the doctor on one of them if we could object and if it was needed. He actually said to me he didn't think my father was injured in the head again, but was doing it as a precaution. He said there's always a small chance you have a bleed. At the time, I asked for time to think about whether to allow it, but I gave in from fear and guilt (that if we didn't spot this, that my dad could die or suffer serious brain damage). He also said it'd take a long time for cancer to develop if the scan did produce it. That combined with some lack of knowledge and being in the heat of the moment made me cave. I regret that one.

One thing he said was E.R. doctors see things very differently from other doctors. They ask what is the worst-case scenario (without considering the odds of it happening) and try to weed it out (often by labs or scans). Many other doctors, he said, have time to observe you for days or weeks. E.R. doctors don't have that luxury. He said they had to make immediate decisions on whether to admit or not and try to protect against the worst scenarios. There was a Harvard and WebMD article that said (paraphrased): NEVER scan just to assure yourself of something. There has to be medical reason for it (I'm guessing decent probability). That's because CTs are powerful tools with much radiation (500x) than a normal x-ray.

 

[jim mcnamara]

https://blog.xkcd.com/2011/03/19/radiation-chart/

will put this in perspective. @.Scott is trying to be helpful, but the cartoon (which is correct) really should help.

Reference: https://www.ncbi.nlm.nih.gov/books/NBK565909/

which says
one x-ray exposes a patient to .01 mSv (like a chest x-ray or dental x-ray)
whole-body computerized tomography (CT) scan is about 10 mSv (worst possible case)
just being alive on earth is 3mSv per year, so if your dad is age >70 he has been exposed to at least 210 mSv.

Read the paper please. You can figure out what a "mSv" unit means from the xkcd comic drawing. Hint: it is
"waaaay down there" in the graphic

 

[gleem]

There is one thing that is very important that has been neglected. The cells of the body have enzymes that repair damage to DNA from chemical carcinogens or radiation. This repair mechanism has been/is neglected in exposures to small doses of radiation although this repair mechanism is used in radiation therapy to great advantage, Why it is neglected is a controversy today. That said some damage does remain and accumulates over time.

WRT the total effect of radiation on cells there are two effects, direct and indirect. In the directed effect the energy of the ionizing radiation is directly transferred to a biological molecule.le resulting in ionization or dissociation. In the indirect effect, the energy of the radiation is transferred to other molecules producing what are known as free radicals, molecules with an unpaired electron. Water making up about 80% of the mass of a cell is the main source of free radicals. Free radicals are very reactive although short-lived (10^-5 sec). When interacting with biological molecules they interfere with normal cellular processes. The repair mechanism can take care of most of this damage. Cells that are largely mitotically inactive, that is do not divide too frequently or not at all are generally quite resistant to radiation.
Mitosis of damaged cells reproduces the damage. Blood stem cells are highly mitotic. This is why leukemia appears so more quickly, It has a short latent period compared to solid tumor cancer. BTW an excess of acute and chronic myeloid leukemias are the only cancers that can be directly attributed to radiation exposure.

It should be noted that the older a person is the less likely that they will develop cancer from a radiation exposure as the latent period is a larger part of their remaining life.

As far as risk estimates go it is generally stated that there is a 5 in ten thousand chance of developing a cancer for every centigray (rad). This should be balanced against the 50% chance of cancer from all causes in one's lifetime. This is based on whole body exposure. Most exams only irradiate a small region of the body. So the risk is reduced further. In addition, the general philosophy of using ionizing radiation is to use it in so far as the risk to the patient is significantly less than the risk of not using it.

For the last seventy or so years the radiology community has made one of its prime goals to reduce the amount of ionizing radiation needed for exams. also known as the As Low As Reasonably Achievable (ALARA) philosophy.

One of the prime reasons that nonmedical persons are not allowed in an X-ray room or near sources of radiation are federal and state regulations which limit the amount of radiation that members of the general public may be exposed to in a given year which is very low. In an X-ray exam, there is always scattered radiation from the patient and some leakage from the X-ray unit.

 

[JT Smith]

I asked the doctor on one of them if we could object and if it was needed. He actually said to me he didn't think my father was injured in the head again, but was doing it as a precaution. He said there's always a small chance you have a bleed.

That kind of gets to the crux of it. The doctor is concerned about a small risk of a potentially serious, possibly deadly, bleed. How do you weigh that risk against a small risk of cancer in 10-20 years? Sure, the patient has had other scans but this is just one scan the doctor is suggesting, not ten. So it's tricky for the doctor. If he doesn't do the scan and there's a problem that is missed it's a tragedy, possibly even a legal issue for him. On the other hand, if he does the test and the patient gets cancer fifteen years later who is to even say that it was due to that particular scan? You can see how a doctor might choose the test, particularly in the case of a patient who isn't young.

It's up to patients to advocate for themselves. It's up to you. But what's the best choice in this situation? It's not obvious.

 

[kyphysics]

But let me describe a plausible example:
An x-ray photon enters your body and strike a salt molecule in the nucleus of one of your cells. In breaks that molecule into a chlorine atom and a sodium atom. The sodium atom interacts with water causing some minor damage, but the chlorine atom then latches onto the side of a DNA molecule causing one of its nucleotides to become non-functional.

At this specific stage, is either the sodium atom that interacted with water in a damaging way and/or the chlorine atom that latched onto DNA & made one of its nucleotides non-functional considered to be cancer at all?

 

[gleem]

I WONDER if the E.R. doctors look at how many scans a person has had in a short period of time before they do another one????

No, I certainly wouldn't expect them to. It's their call. I have worked with physicians for over 30 years, and I noted that specialists do not appreciate the concerns of other specialists. A physician follows the guidelines of his specialty. That is what he answers to, for his conscience and for the courts.

 

[kyphysics]

There is one thing that is very important that has been neglected. The cells of the body have enzymes that repair damage to DNA from chemical carcinogens or radiation. This repair mechanism has been/is neglected in exposures to small doses of radiation although this repair mechanism is used in radiation therapy to great advantage, Why it is neglected is a controversy today. That said some damage does remain and accumulates over time.

In cases where cancer develops then, is it the case that those enzymes simply couldn't repair the specific type of damage done or were they perhaps overwhelmed (like too few enzymes to go after the rapidly growing cancer cells)? Or something else?

 

[gleem]

At this specific stage, is either the sodium atom that interacted with water in a damaging way and/or the chlorine atom that latched onto DNA & made one of its nucleotides non-functional considered to be cancer at all?

This scenario is theoretical. As I noted water is the main factor by a wide margin. The DNA is damaged by the transfer of energy from the free radicals breaking chemical bonds and even severing the DNA strand.

In cases where cancer develops then, is it the case that those enzymes simply couldn't repair the specific type of damage done or were they perhaps overwhelmed (like too few enzymes to go after the rapidly growing cancer cells)? Or something else?

We know if the damage occurs at too fast of a rate and at higher doses that not all damage is repaired. When the doses are low like those from diagnostic X-rays it seems that from some animal experiments, all damage might be repaired. As I noted above repair for radiation exposure limits is not invoked since we cannot do experiments on humans to verify this, particularly since we would need a huge number of persons in the study, and like all human studies there are issues with strict adherence to protocols and controls that would muddle the data. So we end up saying AFAWK all radiation exposure no matter how small carries some risk. Unfortunately, the general public does not or can not put this risk in perspective. For example, there is a 1% chance of dying in an auto accident in your lifetime. 10 CT scans early in life based on the risk estimate above carry an estimated lifetime risk of significantly less than 0.5% since most CT scans are not of the whole body.

 

[.Scott]

At this specific stage, is either the sodium atom that interacted with water in a damaging way and/or the chlorine atom that latched onto DNA & made one of its nucleotides non-functional considered to be cancer at all?

As a matter of practicality, unless it is known to be happening, it is not considered anything.
But in my scenario, it was the chlorine atom that was "carcinogenic", but not yet cancer - since it was what was damaging the DNA.

 

[kyphysics]

Reference: https://www.ncbi.nlm.nih.gov/books/NBK565909/

which says
one x-ray exposes a patient to .01 mSv (like a chest x-ray or dental x-ray)
whole-body computerized tomography (CT) scan is about 10 mSv (worst possible case)
just being alive on earth is 3mSv per year, so if your dad is age >70 he has been exposed to at least 210 mSv.

Read the paper please. You can figure out what a "mSv" unit means from the xkcd comic drawing. Hint: it is
"waaaay down there" in the graphic

Thanks for the info. Very helpful.

W/r/t radiation exposure, I see that chemotherapy and radiation therapy for cancer has as its measure something called a Gy.

1 Gy = 1,000 mSv

One can easily get a dose of 50 Gy in radiation therapy (per Google). That's actually eye-opening given how many mSv that is and the risks associated with treatment.

Also makes you wonder if a cancer treatment can CAUSE more cancer down the line. 50 Gy is massive compared to 15 CT scans (at 10 mSv each).

 

[Rive]

One can easily get a dose of 50 Gy in radiation therapy

Nope. That's for a few grams of cancerous tissue, not for 'one'.
If you check the half-dead dose, it is just 2-6 Gy. For 'one' 50Gy would not be a therapy, but a serious, deadly nuclear accident already.

 

[gleem]

In radiation therapy depending on the type of cancer, the radiation is delivered in daily increments called fractions to some predetermined total dose. A typical fraction is 1.8 Gy. Total doses can range from 30 Gy to 80 Gy. The dose rate is around 1Gy/min.

Yes, cancers can be produced by this treatment often in the area around the high dose region. in the radiation penumbra. However, This is problematic in young cancer patients whose remaining lifetime extends beyond the latent period of the cancer. This is also the area where some of the original cancer cells might have extended and did not receive enough of a dose to eliminate them resulting in a regrowth of the tumor.

 

[Choppy]

Building on the responses above, it's helpful to go back to the difference between absorbed dose, equivalent dose, and effective dose.

Absorbed Dose
This is the physical quantity, defined as the energy deposited per unit mass, measured in Gy, which is equivalent to 1 joule per kilogram.

Equivalent Dose
This is a quantity that accounts, approximately for the biological effectiveness of a given quantity of radiation. A source of alpha particles, for example, can generate a lot more biological damage on a microscopic scale than a photon source, per unit of absorbed dose. So different sources of radiation are given different weighting factors. X-ray sources have a weighting factor of 1. Alphas have a factor of 20. You multiply the absorbed dose by the weighing factor to get an equivalent dose, measured in Sv.

Effective Dose
Now looking in terms of overall effect, different tissues and organs in the body have different sensitivities to the microscopic damage induced by the radiation. Bone marrow, for example is more sensitive than muscle tissue. A second, tissue weighting factor, is used to relate to dose to a particular organ or tissue to a theoretical condition in which the entire body is irradiated to a uniform dose, for the purposes of evaluating the overall health effects of a given exposure. This is also measured in Sv.

So a statement like 1 Gy = 1000 mSv, is only true under certain conditions.

 

[kyphysics]

Nope. That's for a few grams of cancerous tissue, not for 'one'.
If you check the half-dead dose, it is just 2-6 Gy. For 'one' 50Gy would not be a therapy, but a serious, deadly nuclear accident already.

I think gleem's post below reconciles what I meant. By "One," I did not mean one dose.

Rather, I meant "an individual" or "a person" there. As in, "One might misinterpret a text from time-to-time."

In radiation therapy depending on the type of cancer, the radiation is delivered in daily increments called fractions to some predetermined total dose. A typical fraction is 1.8 Gy. Total doses can range from 30 Gy to 80 Gy. The dose rate is around 1Gy/min.

Yes, cancers can be produced by this treatment often in the area around the high dose region. in the radiation penumbra. However, This is problematic in young cancer patients whose remaining lifetime extends beyond the latent period of the cancer. This is also the area where some of the original cancer cells might have extended and did not receive enough of a dose to eliminate them resulting in a regrowth of the tumor.

Thanks for the elaboration and, yes, I did mean total dosage over time could be 50 Gy.

For sure, there's a huge diff. between 1.8 Gy and 50 Gy exposure all at once. Although, the 50 Gy total exposure is still massive when considering what we pick up in a single x-ray or even those horrible CT scans (on average = to 500 x-rays).

I feel for young radiation therapy patients, b/c the risk reward is not so great as with the elderly (who have less to lose).

 

[Rive]

I meant "an individual" or "a person" there.

I took it like that. That's why I wrote that it's for a few grams of cancerous tissue, not for 'one'.

 

[kyphysics]

Equivalent Dose
This is a quantity that accounts, approximately for the biological effectiveness of a given quantity of radiation. A source of alpha particles, for example, can generate a lot more biological damage on a microscopic scale than a photon source, per unit of absorbed dose. So different sources of radiation are given different weighting factors. X-ray sources have a weighting factor of 1. Alphas have a factor of 20. You multiply the absorbed dose by the weighing factor to get an equivalent dose, measured in Sv.

Thanks for the further elaboration. What type of radiation would involve alpha particles?

I take it x-rays and CTs would not have them?

In practice, would there be significantly large differences in equivalent dosage and weighting factor in the radiation from x-rays, CTs, and radiation cancer therapy?

 

[JT Smith]

I take it x-rays and CTs would not have them?

An x-ray is electromagnetic radiation, just like light or radio or microwaves, only higher in frequency. A CT scan is comprised of a series of x-rays so it is the same type of radiation, just more of it.

An alpha particles is a helium nucleus.

You could quickly find a whole list of types of radiation once you have mastered internet searching. There's a useful website called "wikipedia" that could help you to learn more.

 

[gleem]

The units used in radiological physics for measuring radiation and its effects are often used interchangeably by the general public but as noted by Choppy can be quite different. With the possibility of getting into the weeds so to speak, I would add exposure to the units as you still hear, "What was my exposure?". While exposure is related to dose it is different. First, exposure is a quantity that measures the amount of ionization produced by x-rays or gamma rays per unit of mass of air ( the Roentgen which is a legacy unit, symbol R, was the unit of exposure). Dose is typically a calculated quantity and well-defined and can be related to exposure. Dose equivalent and effective dose as one might surmise from Choppy's post are estimates or guidelines used for radiation protection or health estimate purposes

X-ray and Gamma rays produce identical effects no matter the source. Heavy ions as alpha particles release energy at such a high rate that their effect is much more severe. While people are not usually exposed to man-made sources of alpha particles, a natural source of them, Radon from the decay of Uranium in the soil is believed to account for an average of 2/3 of the background radiation dose equivalent.

 

[morrobay]

The units and conversations in this field is a maze. In the Radiation Biology class/lab I took at San Diego State white mice were irradiated with a Westinghouse x-ray. I forget all the data, ie how many Rads (100 ergs/g) they got. We moniteted the decreasing blood cell counts for as long as they lasted, a few weeks. So it would seem a proportional dose in humans would also be fatel.

 

[gleem]

So it would seem a proportional does in humans would also be fatel.

The mouse LD₅₀ the dose needed to kill 50% of a population of mice is about 7 Gy (700 rads). The LD₅₀ for humans is only around 4 Gy (400 rads).

 

[kyphysics]

The units and conversations in this field is a maze. In the Radiation Biology class/lab I took at San Diego State white mice were irradiated with a Westinghouse x-ray. I forget all the data, ie how many Rads (100 ergs/g) they got. We moniteted the decreasing blood cell counts for as long as they lasted, a few weeks. So it would seem a proportional dose in humans would also be fatel.

The mouse LD₅₀ the dose needed to kill 50% of a population of mice is about 7 Gy (700 rads). The LD₅₀ for humans is only around 4 Gy (400 rads).

To check my understanding, are you saying a 4GY dose of radiation (all at once just a single time) would kill a human 50% of the time?

 

[kyphysics]

Radiation may be something I have to learn a lot about. Dad's PET/CT came back showing higher metabolic activity at the site of the nodule. Although never 100% a guarantee of cancer, the radiologist pointed out it's most statistically probable for it. Sometimes, we were told by the doctor, it's a false positive, b/c inflammation can produce the exact same result.

Only way to know for sure is biopsy.

 

[gleem]

To check my understanding, are you saying a 4GY dose of radiation (all at once just a single time) would kill a human 50% of the time?

About half of the humans receiving a 4 Gy dose all at once will die.

 

[hutchphd]

About half of the humans receiving a 4 Gy dose all at once will die.

I think this is better said that "About half of the humans receiving a full body 4 Gy dose all at once will die". Perhaps that is part of the confusion here. The nomenclature here is so very complicated because there are very many blind men looking at a many various elephants.
I had several full body CT scans a few years back and never figured it out completely. I am still healthy, wealthy and wise

 

[Rive]

4GY dose of radiation (all at once just a single time) would kill a human 50% of the time?

That's why it's important that not the whole body gets that dose but only the targeted piece of tissue

One can easily get a dose of 50 Gy in radiation therapy (per Google).

Nope. That's for a few grams of cancerous tissue, not for 'one'.