♥♥♥NATURALLY OCCURRING THORIUM DO NOT CAUSE CANCER WHEN INGESTED OR INHALED (IAEA)
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According to IARC (International Agency for Research on Cancer) Natural Thorium CANNOT CAUSE CANCER WHEN SWALLOWED OR INHALED.
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ATSDR (Agency for Toxic Substances and Disease Registry) of the USA government stated “Thorium was once thought to cause cancer in mine and mill workers, but it was later concluded that thorium likely had no significant impact on their cancer risk. Cancers in these workers were likely due to their cigarette smoking and inhaling silica dust. The International Agency for Research on Cancer (IARC) has NOT FOUND SUFFICIENT EVIDENCE TO CLASSIFY THORIUM IN MINES AND MILLS AS CARCINOGENIC.”
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Natural Uranium which has an activity of 25,400 Bq/g is not regarded as a carcinogen by IARC and yet because of Thorotrast, Thorium 232 with an activity of only 4080 Bq/g is classified as a carcinogen IF GIVEN INTRAVENOUSLY AS A COLLOIDAL SOLUTION OF THORIUM DIOXIDE.
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The main problem is that practically all the papers on Thorotrast do not take into account the massive dose of X-rays radiation patients undergoing Fluoroscopy were subjected to with those archaic X-ray machines...often more than 1,000 mSv.
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If doctors were to use such high doses nowadays, they would be charged for first degree murder!
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Alpha particles has been classified as a carcinogen, but the alpha particles from natural thorium has a very low energy level of only 4.4 MeV and can traverse only 2 to 5 human cell diameters.
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The most abundant gamma rays from Thorium in secular equilibrium is only 12.3 keV (compare this with Potassium which is 1,460 keV).
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Alpha particles are regarded as 20× more harmful than gamma rays..but this is not valid with the lining cells of the gut and respiratory tract...because the life span of these cells is only 4 to 10 days. Cancers take months or years to develop.
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The cells of the gut and respiratory tract die and sloughed off long before they can turn cancerous!
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That may be why IARC has not been able to find any evidence that both natural Thorium and natural Uranium can cause cancers.
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Thorium-232 is considered to be a carcinogen only IF ADMINISTERED INTRAVENOUSLY AS A COLLOIDAL DISPERSION OF THORIUM-232 DIOXIDE." (IARC).
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However, this may not be the complete picture.
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Below are the unknown parameters when calculating the actual biological dose of radiation caused by the Thorium-232 in patients given "Thorotrast Fluoroscopy".
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1. The interval of time when the Thorium-232 was chemically isolated and used to manufacture the "Thorotrast". This is very important as the alpha, gamma and beta activity of varies with time and is lowest 3 years or so after chemical separation and it is only after 60 years when the final equilibrium is achieved.
2. The interval of time before the Thorotrast was actually injected into the patient.
3. The amount of Thorotrast was known to be between 10 ml to 75 ml (3 vials), but in those patients who ultimately develop cancer 20-30 yrs later, the actual amount is not known.
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4. How many fluoroscopic examinations were each of those patients with cancer were subjected to in their lifetime especially those who developed cancers.
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Of all the above factors, the time factor from Thorium-232 chemical isolation to Thorotrast manufacture and to actual parenteral injection of the Thorotrast is the one which is almost impossible to determine though this is very important in the calculation in the biological radiation dose from the Thorium-232.
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The mean latency period for all tumour types was between 25 and 30 years (Frank 1980).
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Most of the papers I have read, the dose of X-ray radiation is unknown and the absorbed dose from the Thorium-232 is also not known.
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Only in one of the studies the mean value of absorbed dose to the liver was given and calculated to be 876 rads for hepatocellular carcinoma and 1053 rads for cholangiocarcinoma (Mori et al. 1983b).
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Unfortunately I have lost the original article of this paper when I moved house, but I cannot remember how this calculation was made...but if we do not know the time interval between the chemical separation of the Thorium-232 and it's final administration to the patient, it is next to impossible to calculate the actual dose.
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Because of the variable nature of the radiation activity of "pure" freshly chemically separated Thorium-232 (Thorium-228 cannot be chemically separated), and even if we know the biological half life the the Thorium-232, it is virtually impossible to estimate the total dose given to these patients.
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When thorium is separated from other isotopes in the decay series, the thorium fraction has only a slight alpha activity.
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There is no beta radiation and only a slight amount of gamma radiation (from the 0.09-MeV gamma rays which emanate from Th-228 decay).
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However, the activity from the Th-228 side of the chain is quickly re-established.
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A first equilibrium state is reached in about 36 days (10 half-lives of Ra-224).
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Activity then declines, as Th-228 decays faster than it is replenished by decaying Ac-228.
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About 3 years after separation, the activity is lower than at any other time except immediately after separation.
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From this point, activity increases until the second equilibrium state is reached in about 60 years.
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There is an initial buildup, decline, and second buildup of alpha and beta activity.\.
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SO IS THORIUM-232 THE REAL CAUSE OF CANCER IN PATIENTS INJECTED WITH THOROTRAST?
Dosage in "Thorotrast" Fluoroscopy = ~1,000 mSv (100 Roentgens)
Risk in developing Cancer = 1 in 20,000 per mSv
Therefore risk with 1 Thorotrast Fluoroscopy = 1 in 20
Therefore in about 4 million patients, number of patients developing Cancers = 200,000 from X-ray induced Cancers!
AND SOME OF THESE PATIENTS MAY HAVE MORE THAN 1 FLUOROSCOPIC EXAMINATION AND NUMEROUS OTHER X-RAYS IN THEIR LIFETIME.
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SO IS IT FAIR TO CONCLUDE THAT THORIUM-232 IS A CARCINOGEN, based mainly on the results of studies on Thorotrast study alone?
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(In an attempt to prevent some injuries, A LIMIT OF 100 ROENTGENS (approximately 1,000 mSv) per fluoroscopic examination was set in New York City hospitals (Braestrup 1969). Prior to this, the dosage from the "Thorotrast" Fluoroscopy may be much higher !
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The International Agency for Research on Cancer ( IARC ) categorized Thorium-232 and its decay products as a group 1 carcinogen when administered intravenously as a colloidal dispersion of thorium-232 dioxide.
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This conclusion was made mainly on the study of certain types of cancers which were found to be increased in patients given Thorotrast for radiological investigations.
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SO IS IT FAIR TO CONCLUDE THAT THORIUM-232 IS A CARCINOGEN, based mainly on the results of studies on Thorotrast study alone?
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Thorotrast was given as a contrast media via the vein or artery and the dose of Thorium used was huge, though this depends on the type of radiological procedure done.
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It had been estimated that as many as 4 million people were given this contrast in the 1930 to late 1950s.
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It has been claimed that there was an increase in the incidence of cancers especially of the liver.
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However, we need to consider a number of factors before we can be sure that this is the real culprit.
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1) The radiation dose from those old X-ray machines in the 1930 to 1950s are hundreds of times that of the present machines.
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For instance an 1896 X-ray machine was tested and found to have exposed the body to 1,500 times more radiation than modern technology does, largely because each image took 90 minutes to develop, dramatically increasing the patient's cumulative exposure to the rays. By 1930 to 1950s, the radiation dose have improved a lot but still much higher than the present X-ray machines.
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Modern day X-rays require only about 21 milliseconds, and technicians place lead coverings over the body to protect vital organs from even this slight exposure.
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Even in the 50s and 60s, the dose of X-rays from Tuberculosis screening is about 100 times higher than that of today's Chest X-Ray.
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The fluoroscope leaves the X-ray beam "on" while the physician does his examination and as such, the fluoroscope has the potential to deliver very high X-ray doses.
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In the 1920s, fluoroscopy became very popular procedure not only among radiologists, but also among many kinds of physicians.
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Radiological methods of diagnosis became so important that no investigation of a patient is considered complete without the X-rays, which generally include fluoroscopy. These studies are often carried out by a general practitioner or surgeon in his office.
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In 1942, Dr. Franz Buschke and Herbert M. Parker wrote (Buschke 1942):
"Recently we became aware of the fact that apparently a number of pediatricians include fluoroscopy in the monthly routine examinations of infants in their care during the first and second years of life." This pediatric practice is confirmed in Pifer 1963 and in Blatz 1970.
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After studying the radiation output of seven fluoroscopes in the offices of "reputable pediatricians selected at random," Buschke and Parker estimated (Buschke 1942, p.527): "If the average rapid fluoroscopy by an experienced and well-adapted examiner takes twenty seconds, about 8.3 roentgens [entrance dose] will be delivered at this rate or 100 roentgens during the first year of life." The roentgen is a dose-unit which is approximately equivalent to a rad (actually it is less as the ICRU defined the roentgen to be 2.58e -4 C/Kg in 1971)
Fluoroscopy was popular also in hospitals.
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(Braestrup 1942, p.213):
"During the past years, we have measured the roentgen output of large numbers of fluoroscopes, using the settings at which they are normally operated ... and have found a very wide variation ... Attention is called particularly to test B-116, where the R [roentgen] per minute at the panel was 127, that is, an erythema dose would be reached in about three minutes. Such a unit could be classified as a lethal diagnostic weapon and yet there are many of these still in use."
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Of the various types of radiologic equipment, the mobile unit probably has been responsible for more radiation damage than any other piece of apparatus. These accidents have in most cases occurred while the mobile unit was used for fluoroscopy by surgeons, who apparently did not realize the high output obtained at short distances."
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In an attempt to prevent some injuries, A LIMIT OF 100 ROENTGENS (approximately 1,000 mSv) per fluoroscopic examination was set in New York City hospitals (Braestrup 1969).
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The patients who received the Thorotrast were subjected to a huge dose of X-rays from these antique X-ray machines.
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This huge dose of X-rays may be the cause of most of the cancers, we just do not know as most of the studies are unable to assess the X-ray's dose. All these studies are done 20 to 30 years later.
So we cannot use other patients who have X-rays done in the 1930s to 1950s as a control group since most X-rays which do not need a contrast media consist of only 1 or 2 X-ray pictures.
A few of the studies do have controls but these controls were cases from later years especially after 1947 when the advancement in radiological techniques and hence dosage reduction is greatest.
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It is generally accepted that the risk of radiation induced cancer is 1 in 20,000 per mSv.
As such, a dose of about 1,000 mSv would mean a risk of 1 in 20. For 4 million patients injected with Thorotrast, THIS RADIATION WOULD GIVE RISE TO AN EXCESS OF 200,000 CASES OF RADIATION INDUCED CANCERS IN THE 4 MILLION CASES OF "THOROTRAST" PATIENTS!
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In 1953, Dade W. Moeller (then of the Public Health Service; later, president of the Health Physics Society) published an estimate that the average entrance dose per fluoroscopic examination was about 65 roentgens (about 650 mSv) at mid-century (Moeller 1953, pp.58-59).
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The use of Thorotrast was discontinued by 1953.
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2) The contrast studies are usually done for patients who are rather ill and may have multiple other disorders.
The cancers usually appear (as most cancers do) about 20 to 30 years later when the patients reach the "cancer" age. Because of this long lapse of cause and effect, all the studies are retrospective in nature.
And as you know, all retrospective studies are full of problems and inaccuracies.
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3) A lot of these patients, have other disorders which may also lead to cancer like alcoholic cirrhosis, hepatitis B and hepatitis C. In fact the first case of liver cancer I saw in Manchester was an old alcoholic with severe liver cirrhosis. But he also had Thorotrast contrast study more than 20 years earlier. Because of this history, the surgeon had to report him as a Thorotrast induced cancer.
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4) With about 4 million by now old people, we are bound to come across a lot of cancer cases. Since the life time risk of cancer in the advanced countries is 1 in 5, there should be about 800,000 cases of cancer due to other causes.
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So how many if any of these (taking into account all the above problems) are really caused by the radiation from the massive dose of intravenous Thorium-232... nobody can be really sure. If anybody says he can tell, then either he is lying or he does not know what he is saying.
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Dr Looi Hoong Wah, FAMM
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