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This is a very long post in reply to some questions of yours.
Ellis: THIS IS ONE OF THE BEST POSTS EVER POSTED ON REJUVENATION, SO I AM GIVING IT 5 STARS (FIVE STARS) WHICH IS A FIRST FOR ME.
I AM CERTAIN IT TOOK DR. MIKE LENKER A LONG LONG TIME TO WRITE IT, AND WHEN YOU READ IT YOU WILL UNDERSTAND WITH WHAT CARE HE ANSWERED.
I WANT TO THANK DR. LENKER FOR TAKING THE TIME TO ANSWER MY QUESTIONS. I ALWAYS SAY THAT I LEARN FROM THE GOOD DOCTORS AND THE PATIENTS AND OTHER SUBSCRIBERS OF REJUVENATION AND THIS IS AN EXAMPLE OF WHAT I MEAN.
I HAVE PUT THIS POST ON A PAGE OF ITS OWN ON MY WEBSITE, SO I WILL LINK TO IT WHEN I HAVE ANSWERS THAT REFER TO X-RAYS AND CAT SCANS, ETC.
RECENTLY A YOUNG BOY TOLD ME THAT HE HAD BEEN TO AN ENDOCRINOLOGIST WHO ORDERED FULL BODY SCANS TO DETERMINE IF HE WOULD STILL GROW TALLER... GIVEN THAT THIS BOY IS 16 YEARS OF AGE AND 6' 4" TALL, THERE WAS ZERO CHANCE THAT THE ENDOCRINOLOGIST WOULD PRESCRIBE GROWTH HORMONE FOR HIM TO GROW TALLER, BUT YET HE MADE THE BOY TAKE FULL BODY X-RAYS. THIS WAS TOTALLY UNNECESSARY, EXPENSIVE, AND ALSO DANGEROUS BECAUSE IT EXPOSED HIM TO UNNECESSARY RADIATION. HE WAS EXPOSED TO X-RAYS IN THE THYROID, BREASTS, AND RED BONE MARROW, WHICH DR. LENKER POINTS OUT ARE SENSITIVE TO RADIATION. - ELLIS -------- Original Message --------
| Subject: | Re: [Rejuvenation] * * * About CT scan, Pet scan, and Radiation |
|---|---|
| Date: | Sun, 05 Oct 2008 23:52:49 -0400 |
| From: mlenker | |
| To: | Rejuvenation@yahoogroups.com |
| References: |
Ellis,
I'm pleased that you want to know my opinions, but people have written books about those topics. My answers are going to be very condensed.
Wikipedia has a great background article on radiation in general at http://en.wikipedia.org/wiki/Radiation
The forms of radiation that matter in the context of x-rays are called ionizing radiation, because, when they strike you, they turn some of the atoms in your tissue into ions. (An ion is an atom or piece of an atom that has an electric charge.) That includes x-rays, gamma rays, and particles emitted when radioactive materials break down. This does NOT include the radio waves that are used to perform MRI imaging, or ultrasound waves used for ultrasound imaging.
Ionizing radiation matters because it can cause cancer. In one stage of pregnancy, in a high enough dose, it can cause malformations. It may also contribute a little bit to aging. Unfortunately, how much cancer is caused by radiation is controversial. That is because most of our information about this depends on people and animals exposed to high doses of radiation. A lot came from studying the survivors of the atomic bombs at Hiroshima and Nagasaki. But, no one knows, if dose X causes 1 case of cancer per ten people exposed, does half of that dose cause half as much cancer? Or less? Or more? Some people think that a little radiation actually prevents cancer.
Most doctors, and the agencies that regulate this stuff, assume that the effect is proportional. If that's the case, medical radiation causes a fair number of cancers (hundreds?) every year in the US. A very rough estimate is that exposing ten thousand people to one centigray (that's a unit of dose) of radiation will cause one cancer. Most CT scans involve a several centigray, but only to part of the body. Most X-rays of the chest and limbs are much less. In general, only the body part being imaged gets much radiation at all. Only a tiny fraction is scattered around the room, and into other parts of the body. The most sensitive organs to radiation are the thyroid gland, the breast (in women) and the red bone marrow (which is mostly in the spine and pelvis.) Children are more sensitive to radiation than adults, especially young children. There is a campaign now in the radiology community to minimize examinations and dose per exam for children, as much as possible.
Considering that 13% of people will eventually die of cancer, and many others get cancer but are cured, you see how hard it is to know if any particular case of cancer was caused by radiation, or by any particular exposure to radiation.
You can't avoid all radiation. It comes from the rocks, it comes from the sky in the form of cosmic rays, and it comes from the breakdown of naturally radioactive materials in your body - materials that have been radioactive since the formation of the earth. Also, many, if not all, of the effects of radiation on tissue are mediated by the creation of free radicals - very reactive compounds that damage other molecules. Unfortunately, free radicals are generated in much greater amounts as a byproduct of oxidative metabolism, without which animals can't live. One theory is that aging is caused by the cumulative effect of free radical damage to tissue, including DNA, in which case radiation could contribute to aging. In my opinion, there is something to that theory, in the case of tissues that are not constantly being replaced. For example, heavy radiation exposure causes accelerated cataracts in the eye (since the lens material is not replaced, once it is deposited.) For most tissues, I think that aging has to be more complicated than that. It does seem to be the case, though, that species with long lives tend to be the species with better protection against free radicals. The fact that caloric restriction reduces the number of free radicals generated may explain at least part of the mechanism for the longevity effect of caloric restriction in many animals.
PET scans are only used in a couple of situations. What they add to CT scans is the ability to show how much glucose is being consumed by a given piece of tissue. Some kinds of cancer eat glucose rapidly, so a PET scan can tell if a little piece of tissue that looks like a lymph node or a scar on CT actually is hiding a cancer. That is the main use today. In patients with a lump that may be a cancer, a PET scan may show that it is one. (But not always, since not all forms of cancer eat a lot of glucose.) Or, if you have a known cancer, the PET scan may show how far it has spread (again, if it is the right kind of cancer.) Another use, that is not so popular in my department, is to look at the brain. PET scans can help classify different forms of dementia, because they affect glucose metabolism in different regions of the brain. Since most of the time there is no good treatment anyway, this is seldom done. PET can also sometimes help find the source of seizures in epilepsy.
The reason any risk at all arises is that the PET scan is done by injecting a form of glucose that is tagged with a radioactive atom. The point is to see what tissue absorbs this tracer, and glucose, by doing a CT scan at the same time. I don't have numbers for how much the tracer increases the radiation dose, but I doubt that it doubles it. The radioactive atoms have a short helf-life of a couple of hours, so they don't stay around long.
As far as the danger of a PET scan, if you already have cancer, the danger is negligible. If you have a lump that might be cancer, it's safer than the alternatives (which would be either surgery to take out the lump, or leaving it alone and hoping for the best.) If you are having a PET scan for dementia, it's safe, because by the time you have dementia, your life span is probably shorter than the ten or twenty years it would take to develop a cancer. Only in the case of epilepsy does the risk become much of a consideration, but these patients have usually exhausted the alternative tests, and their epilepsy is so bad that they are considering brain surgery for it. Compared to the risk of taking out the wrong piece of brain, the small risk of cancer seems not so bad.
MRI is often an alternative to CT scanning, especially in the head and spine, that is not thought to cause cancer, but the scan takes much longer, is more uncomfortable, and is more expensive. MR shows a lot of things in the brain better than CT, but not the sort of things people usually come into the ER for (severe headache, trauma) There are also other nuclear tests than PET-CT, but they all have specific special purposes which I won't take time to list here.
Much of the time, if your doctor wants a scan, it's a good idea to get it. The exceptions are in cases when the thing your doctor wants to rule out is really unlikely, but he wants to be completely sure - because he doesn't have to pay for the test, or suffer if there is any bad consequence from the test itself. This kind of test ordering is the doctor covering his ass, in case he is wrong. I see a lot of this because many of the studies I read are ordered by ER physicians, who get sued a lot. They also don't have much time to get to know the patient, and they don't trust the patient to follow up - for example, they may think someone's belly pain is just indigestion, but if it doesn't get better in a week or so, that would be a different matter. Your home doctor might just keep in touch with you, and get a CT scan in a week if you aren't better. A week would not make any difference if it were a cancer. But since this doctor doesn't know you, he feels like this ER visit is his only chance to make the diagnosis, so he gets all the workup he can, cost be damned.
I think a good question to ask your doctor is, what difference would the result of this test make in my care? If the answer is, "I really don't think it's anything bad, but I just want to be sure," I would see if he/she still felt it was necessary if I really did not want it, and trusted his/her judgement. If the doctor still kind of insisted, though, I would go ahead with the test. The doctor might really think there is a fair chance it's something bad, and just does not want to alarm you until it is confirmed.
By the way, one reason medical costs are out of sight in the US is that it is against the law to turn away anyone from an emergency department, whether they can pay the bill or not. Many people don't pay, so they don't care what their visit costs the hospital. For this reason, they don't bother to have a regular doctor, who would know them, and provide much less costly care. They just come to the ER whenever they have a sniffle, or, in some cities, whenever it's a cold night and they have no warm place to go. Since these are the first people who would sue if they ever have a case, the ER doctors have to overdo it on the testing, to protect themselves.
So... let's start: Please tell us more about RADIATION...
Note: This is a good moment to remember and honor Marie
Curie, (1867-1934) the first woman in France to get a DOCTORATE
in science, and the only woman who was in the company of
Albert Einstein and other great scientists of her days.
Among other things, Marie Curie discovered radium. She
made a huge contribution to our knowledge of radiation and
a huge contribution for MEDICINE, probably at the cost of
her own life. Great pages here:
http://www.aip.org/history/ curie/brief/ index.html
I'm pleased that you want to know my opinions, but people have written books about those topics. My answers are going to be very condensed.
Wikipedia has a great background article on radiation in general at http://en.wikipedia.org/wiki/Radiation
The forms of radiation that matter in the context of x-rays are called ionizing radiation, because, when they strike you, they turn some of the atoms in your tissue into ions. (An ion is an atom or piece of an atom that has an electric charge.) That includes x-rays, gamma rays, and particles emitted when radioactive materials break down. This does NOT include the radio waves that are used to perform MRI imaging, or ultrasound waves used for ultrasound imaging.
Ionizing radiation matters because it can cause cancer. In one stage of pregnancy, in a high enough dose, it can cause malformations. It may also contribute a little bit to aging. Unfortunately, how much cancer is caused by radiation is controversial. That is because most of our information about this depends on people and animals exposed to high doses of radiation. A lot came from studying the survivors of the atomic bombs at Hiroshima and Nagasaki. But, no one knows, if dose X causes 1 case of cancer per ten people exposed, does half of that dose cause half as much cancer? Or less? Or more? Some people think that a little radiation actually prevents cancer.
Most doctors, and the agencies that regulate this stuff, assume that the effect is proportional. If that's the case, medical radiation causes a fair number of cancers (hundreds?) every year in the US. A very rough estimate is that exposing ten thousand people to one centigray (that's a unit of dose) of radiation will cause one cancer. Most CT scans involve a several centigray, but only to part of the body. Most X-rays of the chest and limbs are much less. In general, only the body part being imaged gets much radiation at all. Only a tiny fraction is scattered around the room, and into other parts of the body. The most sensitive organs to radiation are the thyroid gland, the breast (in women) and the red bone marrow (which is mostly in the spine and pelvis.) Children are more sensitive to radiation than adults, especially young children. There is a campaign now in the radiology community to minimize examinations and dose per exam for children, as much as possible.
Considering that 13% of people will eventually die of cancer, and many others get cancer but are cured, you see how hard it is to know if any particular case of cancer was caused by radiation, or by any particular exposure to radiation.
You can't avoid all radiation. It comes from the rocks, it comes from the sky in the form of cosmic rays, and it comes from the breakdown of naturally radioactive materials in your body - materials that have been radioactive since the formation of the earth. Also, many, if not all, of the effects of radiation on tissue are mediated by the creation of free radicals - very reactive compounds that damage other molecules. Unfortunately, free radicals are generated in much greater amounts as a byproduct of oxidative metabolism, without which animals can't live. One theory is that aging is caused by the cumulative effect of free radical damage to tissue, including DNA, in which case radiation could contribute to aging. In my opinion, there is something to that theory, in the case of tissues that are not constantly being replaced. For example, heavy radiation exposure causes accelerated cataracts in the eye (since the lens material is not replaced, once it is deposited.) For most tissues, I think that aging has to be more complicated than that. It does seem to be the case, though, that species with long lives tend to be the species with better protection against free radicals. The fact that caloric restriction reduces the number of free radicals generated may explain at least part of the mechanism for the longevity effect of caloric restriction in many animals.
This is a complicated question. CT scans are used a lot in the brain to look for bleeding, tumors and sometimes strokes. They are used in the abdomen to look for tumors, bowel obstruction, injuries, and appendicitis and other inflammatory bowel disease. They are great for looking at the spine for fractures, and fair for other spinal conditions. There are many other, less common, applications. If you could slice the patient up like a salami and be able to see the answer to the question by looking at the slices, then you can usually answer the question with a CT scan. The CT scan does not tell you anything about how well most organs in the body are functioning, though, unless the malfunction somehow changes the shape of an organ.So... on with the interview. When would you use a CT
("cat") scan, and when would you use a PET scan?
How "dangerous" or should I say, how "safe" is a PET scan?
What are the pros and cons of taking a PET scan?
PET scans are only used in a couple of situations. What they add to CT scans is the ability to show how much glucose is being consumed by a given piece of tissue. Some kinds of cancer eat glucose rapidly, so a PET scan can tell if a little piece of tissue that looks like a lymph node or a scar on CT actually is hiding a cancer. That is the main use today. In patients with a lump that may be a cancer, a PET scan may show that it is one. (But not always, since not all forms of cancer eat a lot of glucose.) Or, if you have a known cancer, the PET scan may show how far it has spread (again, if it is the right kind of cancer.) Another use, that is not so popular in my department, is to look at the brain. PET scans can help classify different forms of dementia, because they affect glucose metabolism in different regions of the brain. Since most of the time there is no good treatment anyway, this is seldom done. PET can also sometimes help find the source of seizures in epilepsy.
The reason any risk at all arises is that the PET scan is done by injecting a form of glucose that is tagged with a radioactive atom. The point is to see what tissue absorbs this tracer, and glucose, by doing a CT scan at the same time. I don't have numbers for how much the tracer increases the radiation dose, but I doubt that it doubles it. The radioactive atoms have a short helf-life of a couple of hours, so they don't stay around long.
As far as the danger of a PET scan, if you already have cancer, the danger is negligible. If you have a lump that might be cancer, it's safer than the alternatives (which would be either surgery to take out the lump, or leaving it alone and hoping for the best.) If you are having a PET scan for dementia, it's safe, because by the time you have dementia, your life span is probably shorter than the ten or twenty years it would take to develop a cancer. Only in the case of epilepsy does the risk become much of a consideration, but these patients have usually exhausted the alternative tests, and their epilepsy is so bad that they are considering brain surgery for it. Compared to the risk of taking out the wrong piece of brain, the small risk of cancer seems not so bad.
MRI is often an alternative to CT scanning, especially in the head and spine, that is not thought to cause cancer, but the scan takes much longer, is more uncomfortable, and is more expensive. MR shows a lot of things in the brain better than CT, but not the sort of things people usually come into the ER for (severe headache, trauma) There are also other nuclear tests than PET-CT, but they all have specific special purposes which I won't take time to list here.
Much of the time, if your doctor wants a scan, it's a good idea to get it. The exceptions are in cases when the thing your doctor wants to rule out is really unlikely, but he wants to be completely sure - because he doesn't have to pay for the test, or suffer if there is any bad consequence from the test itself. This kind of test ordering is the doctor covering his ass, in case he is wrong. I see a lot of this because many of the studies I read are ordered by ER physicians, who get sued a lot. They also don't have much time to get to know the patient, and they don't trust the patient to follow up - for example, they may think someone's belly pain is just indigestion, but if it doesn't get better in a week or so, that would be a different matter. Your home doctor might just keep in touch with you, and get a CT scan in a week if you aren't better. A week would not make any difference if it were a cancer. But since this doctor doesn't know you, he feels like this ER visit is his only chance to make the diagnosis, so he gets all the workup he can, cost be damned.
I think a good question to ask your doctor is, what difference would the result of this test make in my care? If the answer is, "I really don't think it's anything bad, but I just want to be sure," I would see if he/she still felt it was necessary if I really did not want it, and trusted his/her judgement. If the doctor still kind of insisted, though, I would go ahead with the test. The doctor might really think there is a fair chance it's something bad, and just does not want to alarm you until it is confirmed.
By the way, one reason medical costs are out of sight in the US is that it is against the law to turn away anyone from an emergency department, whether they can pay the bill or not. Many people don't pay, so they don't care what their visit costs the hospital. For this reason, they don't bother to have a regular doctor, who would know them, and provide much less costly care. They just come to the ER whenever they have a sniffle, or, in some cities, whenever it's a cold night and they have no warm place to go. Since these are the first people who would sue if they ever have a case, the ER doctors have to overdo it on the testing, to protect themselves.
If a patient has cancer, how EFFECTIVE is radiation
in treating cancer? About what percentage of patients
are completely cured because of radiation treatment?
I only do diagnostic
radiology, not radiation therapy. But I can answer the question
generally. This one
is also complicated, because there are dozens, if not hundreds, of
different kinds of cancer, and even within each kind, all individuals
don't respond the same. Some kinds respond very well to radiation
(choriocarcinoma, some kinds of lymphoma). Most kinds respond somewhat.
A few don't respond at all. The problem is that, after a certain stage,
the cancer cells are spread to other parts of the body. Those cells may
grow into more tumors, years after the original tumor has been cut out,
or irradiated. Unfortunately, you can't irradiate the whole body as
much as you can treat one part of it, without killing the patient. (For
the whole body, a lethal dose is about 650 centigray, all at once. A
typical dose for radiation therapy might be 4800 centigray, to a body
part.) For this reason, radiation is seldom used to attempt to cure a
cancer, all by itself. It can be used in combination with surgery
and/or chemotherapy in an attempt at a cure, or it can be used by
itself to treat a region involved by a tumor. One place it works well
is in combination with surgery for breast cancer, for a cure (the
surgeon can sometimes take less of the breast, if the area is then
going to be treated with radiation.) One place it is often used for
palliation is in the spine. Someone with tumors all over may be
suddenly paralyzed by a tumor in the spine. Radiating that one tumor
may give the patient back the use of his/her legs for the few weeks or
months they have left to live. In that case, the treatment may not
prolong their life at all; it just lets them get more out of their
time.
There are tumors that occur in places that they can't be removed from, such as certain parts of the brain, or in the chest, attached to the aorta or the heart. Often radiation therapy can shrink those tumors, giving the patient extra months to years of life, compared to doing nothing. Most of those tumors eventually grow back, but not all of them. I don't have overall statistics, and they would not mean anything because in each case it depends on the kind of cancer, and exactly where it sits. The side effects also depend on the area of the tumor, since the radiation will affect the nearby organs.
There are tumors that occur in places that they can't be removed from, such as certain parts of the brain, or in the chest, attached to the aorta or the heart. Often radiation therapy can shrink those tumors, giving the patient extra months to years of life, compared to doing nothing. Most of those tumors eventually grow back, but not all of them. I don't have overall statistics, and they would not mean anything because in each case it depends on the kind of cancer, and exactly where it sits. The side effects also depend on the area of the tumor, since the radiation will affect the nearby organs.
How DANGEROUS is it for YOU to be a RADIOLOGIST? How much
radiation are YOU exposed to in your work?
Mike Lenker
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