W. Gofman, M.D., Ph.D.
Egan O'Connor, Executive Director of CNR
Introduction: What Kind of Radiation Are We Talking About?
During our 25 years of experience at the Committee for Nuclear Responsibility (CNR), we have received certain questions again and again. Question #1 is the most frequent, by far.
The type of radiation which this Committee addresses is ionizing radiation. This type includes xrays, gamma rays, beta particles, alpha particles, and lots of other high-energy particles (neutrons, positrons, etc.). Ultra-violet radiation is generally treated as a separate class.
Xrays and gamma rays, which are a type of electro-magnetic radiation, are far more energetic per photon than visible light, and immensely more energetic per photon than microwaves and radiowaves. Nonetheless, xrays and gamma rays do their biological damage via particles, especially electrons. The rays can (and do) make some electrons in our cells start traveling like high-speed rockets through the home-cell and neighboring cells. These "unnatural" electrons are just like beta particles, except for origin. Beta particles are ejected as high-speed electrons from inside the nucleus of an unstable atom, whereas high-speed electrons are orbiting outside a nucleus when they are "kicked" into travel by a photon. Very high-energy photons (>1.02 MeV) can create high-speed electrons and positrons (a conversion of energy into mass).
Regardless of their origin, as high-speed particles slow down, they transfer unnaturally large amounts of energy at irregular intervals to various cells. These transfers of too much energy are unlike the smaller energy-transfers in routine body-chemistry, and the bigger transfers can cause complex, non-repairable damage to a cell's library of genetic instructions --- the chromosomes and DNA. Some types of permanent injury kill the cell, but other types do not.
If the radiation-injured cell does not die, a damaged chromosome or damaged piece of DNA can result in benign and malignant tumors. If the injured chromosome or DNA is in the germ-line (in a "sex cell"), the result can be afflictions suffered by descendants of the irradiated person.
Separate from ionizing radiation is the investigation of biological impacts from electrical fields, magnetic fields, microwaves, radiowaves, "wireless" personal communications, and radar. These are very important topics in which CNR has no expertise. A citizen-group concerned with these radiations is the EMR Alliance, 410 West 53rd Street, Suite 402, New York City 10019. Tel: 212-554-4073. $35 per year.
An independent, professional publication (bi-monthly) on non-ionizing radiations is Microwave News, Post Office Box 1799, Grand Central Station, New York City 10163. $285 per year. If your library-system does not yet subscribe to MWN, the librarian should ask MWN for a free sample copy of this excellent publication. It is hard to see how citizens can participate in decisions about non-ionizing radiation if librarians fail to provide this essential source of current information on the newest scientific studies, meetings, etc. On the Internet: <http://www.microwavenews.com/>
- LIST OF QUESTIONS
What amount of radiation is safe?
Among the proven causes of human cancer, how important is radiation?
Can one case of cancer have more than one cause?
When you estimate that 75% of recent and current breast-cancer in the USA is due to earlier exposure to medical irradiation, do you mean that all other agents combined are responsible for only 25% of the cases?
What makes your estimate 75%, when some other estimates are as low as 1% to 10% ?
How can radiation both be a cause of cancer and also be used to treat cancer?
Should I have radiation therapy to treat my cancer?
Will regular mammograms protect me from breast cancer, or will they give me breast cancer?
Just how big is the chance that mammography will give a woman breast cancer?
Aren't some people more sensitive to radiation than the average person?
Which is worse, external radiation or internal radiation?
How much extra radiation do we receive from flying?
Why do some sources say our average dose from natural background is 100 milli-rems per year, and other sources say the dose is 250 milli-rems or more? Who's right?
Rads, rems, grays, sieverts, effective dose equivalents, roentgens --- how can we cope with such terms?
How much extra radiation dose do I get from a smoke detector?
What is a "curie" of radiation?
Which is more dangerous --- a radioactive substance with a short half-life or a long half-life?
1 What amount of radiation is safe?
Safe means free from danger or risk. Safer means more nearly free from risk than something else. Safest means the most nearly free from risk than other things under discussion. Even the safest car is not safe (risk-free). And even the smallest exposure to ionizing radiation is not safe (risk-free), with respect to cancer and inherited afflictions. In other words, there is no "threshold" dose-level below which all cancer-risk from radiation disappears.
The amount of the danger or risk depends on the amount of radiation exposure. The only risk-free (safe) dose is zero-dose, with respect to unrepairable injury of chromosomes and DNA. We proved this in CNR's 1990 book, by any reasonable standard of scientific proof (Gofman 1990). In 1993, the United Nations Scientific Committee on Effects of Atomic Radiation supported the same conclusion (UNSCEAR 1993). And in 1995, Britain's National Radiological Protection Board also concluded that the weight of the evidence "falls decisively in favor of" the no-threshold conclusion for benign and malignant tumors (NRPB 1995).
When an individual receives a small extra dose of radiation, the person receives a small extra risk of cancer --- say, 1 chance in 1,000. The person has 999 chances out of 1,000 of escaping. But if 25,000,000 people like that individual each receive the same, small extra dose of radiation, each person receives 1 chance in 1,000. The consequence is a rate of 25,000 extra cancers in that group. Point: A small personal risk can mean a large actual rate for a group --- a fact which produces important ethical and health issues.
2 Among the proven causes of human cancer, how important is radiation?
We think that ionizing radiation is very probably the single most important human carcinogen of the 20th century. In 1997, CNR will publish a study which is consistent with that hypothesis.
Other proven human carcinogens include certain viruses and chemical substances (including asbestos and tobacco smoke). Specific chemicals sometimes cause only specific types of cancer. By contrast, we predicted in 1969 that "All forms of cancer, in all probability, can be increased by radiation." This warning met with resistance from the radiation community, and we were called "controversial" (and worse). But by 1980, the radiation committee of the National Academy of Sciences acknowledged that "Cancer may be induced by radiation in nearly all the tissues of the human body" (BEIR 1980, Section 5).
An extremely important question remains unsettled, however. Do the various carcinogens work synergistically (as co-factors, multiplying the potency of each other), or do they work additively (as independent agents having a fixed potency in every situation and in every nation)? We predict that they usually work as synergists. If correct, then reducing exposure to ionizing radiation --- which would be easy to do --- would also reduce the impact of many other carcinogens.
3 Can one case of cancer have more than one cause?
Most experts currently accept (a) the single-cell origin of a cancer and (b) the requirement for multiple genetic abnormalities in the same cell. It follows that a single case of cancer very probably has more than one cause, even if carcinogens act additively instead of synergistically.
Suppose that a type of cancer requires the accumulation of 5 independent genetic injuries in the same cell. If only 4 occur, no cancer can occur. But each of the 5 injuries required (in this supposition) to produce one case of cancer, could be caused in the same cell by a different carcinogen. Some such injuries are surely inherited.
4 When you estimate that 75% of recent and current breast-cancer in the USA is due to earlier exposure to medical irradiation, do you mean that all other agents combined are responsible for only 25% of the cases?
No, we don't. Our 75% incorporates a very big role for non-radiation agents, because it explicitly incorporates the assumption of synergy between them and radiation, with the other agents causing each unit of radiation to be much more potent in causing breast cancer in the USA than in Japan (Gofman 1995/96, Chapters 40 + 47).
5 Why is your estimate 75%, when some other estimates are as low as 1% to 10% ?
Anyone who assumes that causes of breast-cancer act independently (additively) can divide our estimate by 6. Everyone must choose assumptions, because evidence is still too meagre to settle the issue (as stated in Question 2). The "additive" assumption converts 75% to 12.5% (Gofman 1995/96, p.313).
In addition, analysts who still treat medical xrays identically with atomic-bomb radiation cut our estimate in half. So they convert 12.5% to 6.25%. Such analysts ignore the evidence that xrays are at least 2 times more potent than A-bomb radiation per dose-unit (Gofman 1995/96, pp.337-338).
The estimate of 1% incorporates irrelevant dose-estimates which are over 10 times lower than the relevant dose-estimates (Gofman 1995/96, pp.314-315).
6 How can radiation both be a cause of cancer and also be used to treat cancer?
The "current wisdom" is that cancer begins with a single cell having abnormal genetic instructions. Over time, it (or one of its descendant cells) acquires additional injuries. Finally, a cell's abnormal instructions cause it to do abnormal things --- such as dividing too often, or forming a tumor, or migrating from its appropriate location to live and divide elsewhere in the body (metastasis). These cancerous activities are done by living cells, whose abnormalities can be caused by radiation.
When radiation is used to treat cancer, it is used in very high doses which do enough damage to kill cells. Dead cells cannot behave like cancer. It is very difficult to give radiation only to cancer cells, without giving both high and low doses of radiation to healthy cells in the neighborhood. Methods in radiation therapy are improving with time.
7 Should I have radiation therapy to treat my cancer?
We think informed consent is an important principle in medicine (and in every voluntary transaction).
We hear from too many women with breast cancer whose own physicians told them only about the benefits from radiation therapy --- but not about the side-effects which sometimes occur on the irradiated side --- such as chronic swelling of the arm, chronic pain in the arm, paralysis of the arm (from radiation damage to its nerve), broken ribs (from radiation damage to bone), or radiation damage to the underlying lung or heart. Unavoidably, the non-cancerous breast also receives considerable radiation exposure.
Patients who consider radiation therapy for abdominal cancers may also want to ask for details about potential complications from radiation damage involving the bladder, intestines, ureters, kidneys, nerves, spine, etc.
CNR has no expertise in treating any type of cancer. Our focus is on helping to prevent cancer.
8 Will regular mammograms protect me from breast cancer, or will they give me breast cancer?
Mammograms never prevent breast cancer. They may help to discover a cancer which already exists, and then the treatment which follows the discovery may help protect a woman from dying of the cancer.
Unlike earlier decades, the radiation dose from each mammographic exam today can be quite low, which means the average risk of getting cancer from the exam is not high (see Question 9). At accredited mammography centers in the USA, the maximum mean glandular dose from a 2-view exam is now 0.6 rad (600 milli-rads). Actual doses are often lower, like 0.2 rad per 2-view exam. Dose is mostly confined to the breasts.
9 Just how big is the chance that mammography will give a woman breast cancer?
Below, we will give three examples from Gofman 1995/96. Estimates are based on the premise that the mean absorbed glandular dose is 0.2 rad from a 2-view exam.
Suppose a woman age 50 has one 2-view mammographic exam. Our estimate is that the average woman would have 1 chance in 2,041 of getting breast cancer from that single exam. In other words, 1 woman out of every 2,041 such women would develop breast cancer because of the mammogram.
Suppose a woman has 15 mammograms beginning at age 50. Then we estimate that the average woman would accumulate 1 chance in 136 of getting breast cancer because of the exams.
Suppose a woman has annual mammograms beginning at age 40. By age 65, she has taken 25 exams. Then we estimate that the average woman would have accumulated approximately 1 chance in 81 of getting breast cancer because of the exams.
Other analysts claim that the risk is much lower, for the first two reasons discussed in Question 5.
10 Aren't some people more sensitive to radiation than the average person?
Yes, almost certainly. But there is no way to identify them --- yet. For instance, several different genes provide every cell with the ability to repair routine injuries to chromosomes and DNA. People who are born with a faulty "repair gene" in every cell, are going to be more vulnerable than the average person to cancer induced by radiation and by other carcinogens (mutagens).
When analysts study the cancer-response to radiation in human groups, the sensitive individuals are probably contributing much of the response. Therefore, the unlucky sensitive women are going to have higher risks from mammography than the average values in Question 9, and other women will have lower risks than indicated in Question 9.
11 Which is worse, external radiation or internal radiation?
To a cell, all high-speed electrons feel alike, except for their particular energy (Introduction). A cell does not know why such electrons are there. And a cell does not care whether they come because of an external source (like an x-ray machine or a radium dial) or because of a radioactive substance inside you (for example, cesium-137, strontium-90, iodine-131). But the cell cares a lot about the number of such electrons, because (at equal energy per electron) the damage is proportional to the number.
Unlike xrays and gamma rays (photons), radioactive substances (radio-nuclides) have chemical properties, and the body uses them chemically. For instance, the body collects iodine in the thyroid gland. Therefore, thyroid cells experience many more high-speed electrons (and more damage) than do breast cells from internal radio-iodine.
12 How much extra radiation do we receive from flying?
Radiation exposure, from natural cosmic sources, increases with altitude, with peak dose at about 45,000 feet. Dose from cosmic radiation also varies with latitude; it is lowest near the equator and highest near the poles. Therefore, the extra radiation dose from flying depends on (a) the particular route, (b) the duration of the flight, and (c) the fraction of the trip spent below the flight's maximum altitude.
A useful "ballpark" value for a nonstop commercial flight, from California to New York and back, is an extra dose to all your organs of about 0.003 rem (3 milli-rems). Such a trip adds about 3% to the average annual whole-body dose from all natural radiation combined --- which is about 100 milli-rems per year of whole-body exposure in the USA, on the average.
13 Why do some sources say our average dose from natural background is 100 milli-rems per year, and other sources say the dose is 250 milli-rems or more? Who's right?
There is no contradiction. There is just some carelessness in specifying what each number describes.
100 milli-rems per year refers to the average annual whole-body exposure. Every organ is at risk, including the ovaries and testes. The figure of 100 milli-rems per year excludes exposure by natural radon and thoron because these radio-nuclides and their radioactive decay-products cause primarily lung-exposure, rather than primarily whole-body exposure.
250 milli-rems of annual effective dose equivalent is a number which combines the whole-body exposure with the partial-body exposure --- by applying a long series of assumptions about the relative importance of each organ, in terms of health consequences.
14 Rads, rems, grays, sieverts, effective dose equivalents, roentgens --- how can we cope with such terms?
The rad is the most "solid" unit of biological dose, because it contains no assumptions. A rad is defined as a certain amount of energy deposited by high-speed particles per gram of biological tissue (Introduction). Rads and roentgens are almost equivalent. The gray is the name for 100 rads.
The rem is a unit which incorporates some evidence and some assumptions about the relative harmfulness of various high-speed particles, even when they deliver the same amount of energy per gram of biological tissue. In general, the rad and the rem are equivalent only when discussing gamma rays (or certain xrays). The sievert is the name for 100 rems.
The effective dose equivalent, which is always expressed in rems or sieverts, incorporates many additional assumptions about biological consequences (details in Gofman 1995/96, pp.358-359). "Effective doses" and rad-doses are not directly comparable.
15 How much extra radiation dose do I get from a smoke detector?
Very, very little. If you have a photo-electric smoke detector, there is no radioactive substance in it. If you have the much more common "ionization" type, there is a radio-nuclide in it --- usually 1 micro-curie of americium-241. A micro-curie is one-millionth of one curie (Question 16). Americium-241 emits alpha particles (Question 17), which are kept inside the case. It also emits some gamma radiation which can penetrate the case. We measured the gamma dose-rate from our own smoke detector, and 3 feet away from it, the extra dose-rate was 1/80 of a micro-rad per hour --- 1/80 of one millionth of a rad. To receive one extra milli-rad of gamma dose from our detector, we would have to sit 3 feet away from it for about 80,000 hours.
16 What is a "curie" of radiation?
A curie is the amount of a pure radio-nuclide which can decay into a different substance at the rate of 37 billion atoms per second. Decay means changes in the atomic nucleus. The curie is not a measure of biological dose. The dose (in rads) is a separate piece of information.
Each pure radioactive species is characterized by what fraction of its remaining atoms are decaying during a unit of time (second, minute, year). The radioactive half-life is the time required for half of the atoms in any pure radioactive sample to decay into a different species.
17 Which is more dangerous --- a radioactive substance with a short half-life or a long half-life?
Two opposite answers are possible! To understand why, one must consider the very simple --- but amazing --- law of radioactive decay, which is: The fraction of atoms (of a pure radio-nuclide) decaying per unit of time equals 0.693 divided by the radioactive half-life. If the half-life is expressed in years, then the fraction decaying is "per year." (Details in Gofman 1981, pp.33-36).
The radioactive half-life of plutonium-239 is about 24,400 years, compared with about 88 years for plutonium-238. The way their atoms decay is comparable: Each atom ejects (out of its nucleus) a high-speed alpha particle having over 5 million electron-volts of energy. An alpha particle consists of 2 protons plus 2 neutrons; the particle carries a +2 electrical charge; it interacts so fiercely with tissue that it "spends" all of its kinetic energy within just a few cells.
Is it more dangerous to have 100,000 atoms of Pu-239 in your body, or 100,000 atoms of Pu-238?
The fraction of Pu-239 atoms decaying per year = 0.693 / 24,400 years = 0.000028402. So, during the first year, the number of atoms decaying = 100,000 atoms times 0.000028402 = 2.8 atoms. Since there are no fractional atoms, we'll say 3 atoms. The fraction of Pu-238 atoms decaying per year = 0.693 / 88 years = 0.007875. So, during the first year, the number of atoms decaying = 100,000 atoms times 0.007875 = 788 atoms --- lots more than 3.
During the second year, the decayed atoms are no longer available to decay. So the number of Pu-239 atoms decaying = 99,997 available atoms x 0.000028402 = 2.84 atoms, or 3 again. The number of Pu-238 atoms decaying = 99,212 atoms x 0.007875 = 781 atoms --- still lots more than 3.
Since the biological damage per year is proportional to the number of decaying atoms, the Pu-238 will remain much more dangerous, if you start with equal numbers of atoms.
by contrast, the Pu-239 will do slightly more damage than the Pu-238, if you start with equal curies --- or partial curies (e.g., a nano-curie: "only" 37 decays per second).
Many more atoms of Pu-239 than Pu-238 are required to produce an equal number of decays per second. Why? The fraction of Pu-238 atoms decaying per unit time is about 277 times larger than the fraction of Pu-239 atoms decaying per unit time. An example of equal decays from unequal number of atoms: (1,000,000 Pu-238 atoms) x (0.007875) = 7,875 decays during first year. And: (277,000,000 Pu-239 atoms) x (0.000028402) = 7,867 decays during first year --- the same.
Initially equal curies of Pu-239 and of Pu-238 cause equal decays (equal damage) during the first year. But during every subsequent year, the remaining Pu-238 atoms eject fewer alpha particles per year than the remaining Pu-239 atoms. That is because a smaller fraction remains of the original Pu-238 atoms than the original Pu-239 atoms. The ratio of remaining atoms is no longer 277. This being the case, the two samples cannot continue to generate equal decays per year, as they did at the outset. Pu-239 generates more than Pu-238.
In diagnostic nuclear medicine, radio-nuclides are measured in fractional curies. With initially equal curies of two nuclides having comparable biochemical behavior, shorter half-life means less radiation dose than longer half-life.
# # # # #
BEIR 1980: Committee on the Biological Effects of Ionizing Radiation, National Academy Press, Effects on Populations of Exposure to Low Levels of Ionizing Radiation. ISBN 0-309-03075-7.
Gofman 1981 (John W.): Radiation and Human Health. Sierra Club Books, $29.95. ISBN 0-87156-275-8.
Gofman 1990 (John W.): Radiation-Induced Cancer. CNR Books, $29.95. ISBN 0-932682-89-8. Also on Internet.
Gofman 1995/96 (John W.): Preventing Breast Cancer. CNR Books, $17. 1st Edition 1995. 2nd Edition 1996. ISBN 0-932682-96-0. Also on Internet.
NRPB 1995: Nat'l Radiological Protection Board (Britain), Risk of Radiation-Induced Cancer at Low Doses. Ten British pounds. ISBN 0-85951-386-6.
UNSCEAR 1993: United Nations Sci. Com'tee on Effects of Atomic Radiation, 1993 Report to the General Assembly, with Scientific Annexes. $90. ISBN 92-1-142200-0.
Committee for Nuclear Responsibility, Inc. (CNR)
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