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Sabtu, 30 Juni 2018

Harnessing the Potential of Radiation-Induced Immune Modulation ...
src: cancerimmunolres.aacrjournals.org

Up to 10% of invasive cancers are associated with radiation exposure, including ionizing radiation and non-ionizing radiation. In addition, most non-invasive cancers are non-melanoma skin cancer caused by non-ionizing ultraviolet radiation. The ultraviolet position in the electromagnetic spectrum is at the boundary between ionizing radiation and non-ionizing radiation. Non-ionizing radio frequency radiation from cell phones, electric power transmissions, and other similar sources has been described as a possible carcinogen by the International Agency for the International Agency for Cancer Research, but the relationship remains unproven.

Exposure to ionizing radiation is known to increase the incidence of cancer in the future, especially leukemia. This mechanism is well understood, but the quantitative model predicts the level of risk remains controversial. The most widely accepted model argues that the incidence of cancer from ionizing radiation increases linearly with an effective radiation dose at a rate of 5.5% per sievert. If the linear model is correct, then natural background radiation is the most dangerous source of radiation for public health, followed by medical imaging for a second.


Video Radiation-induced cancer



Cause

According to a general model, radiation exposure may increase the risk of cancer. Typical contributors to such risks include natural background radiation, medical procedures, occupational exposure, nuclear accidents, and many others. Some of the major contributors are discussed below.

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Radon is responsible for the majority of the world over from public exposure to ionizing radiation. It is often the largest contributor to individual background radiation doses, and is the most varied variable from location to location. Radon gas from natural sources can accumulate in buildings, especially in restricted areas such as attics, and dungeons. It can also be found in some springs and hot springs.

Epidemiological evidence suggests a clear link between lung cancer and high radon concentrations, with 21,000 lung deaths from lung cancer in the United States per year - second only to smoking - according to the US Environmental Protection Agency. Thus in the geographic area where radon is present in high concentrations, radon is considered a significant indoor air contaminant.

Residential exposure to radon gas has the same cancer risk as passive smokers. Radiation is a potential source of cancer when combined with other cancer-causing agents, such as exposure to radon gas plus tobacco smoking.

Medical

In industrialized countries, medical imaging accounts for nearly as much radiation dose to the public as natural background radiation. The collective dose for Americans from medical imaging grew by a factor of six from 1990 to 2006, largely due to the increasing use of 3D scans that provided more doses per procedure than traditional radiography. The CT scan itself, which includes half the dose of medical imaging to the public, is estimated to be responsible for 0.4% of current cancers in the United States, and this may increase to as high as 1.5-2% with 2007 CT usage rates; However, these estimates are debatable. Other nuclear medicine techniques involve direct injection of radioactive drugs into the bloodstream, and intentional radiotherapy treatments provide a lethal dose (at the cellular level) to tumors and surrounding tissues.

It is estimated that a CT scan performed in the US in 2007 alone will result in 29,000 new cases of cancer in the coming years. This estimate was criticized by the American College of Radiology (ACR), which maintains that the life expectancy of CT-scanned patients is not that of the general population and that the model of counting cancer is based on total-body radiation exposure and is thus damaged.

Jobs

In accordance with ICRP recommendations, most regulators allow nuclear energy workers to receive up to 20 times more radiation doses than are allowed for the general public. Higher doses are usually permitted when responding to emergencies. The majority of workers are routinely well guarded within regulatory limits, while some important technicians will routinely approach their maximum each year. Unintentional overexposures beyond the limits of regulation occur globally several times a year. Astronauts on long missions are at higher risk of cancer, see cancer and outer space.

Some jobs are exposed to radiation without being classified as nuclear energy workers. Airline crews receive job exposure from cosmic radiation as it reduces the atmospheric shield at altitude. Mining workers receive job exposure to radon, especially in uranium mines. Anyone working in a granite building, like the US Capitol, is likely to receive doses of natural uranium in granite.

Unintentional

Nuclear accidents can have dramatic consequences on their environment, but their global impact on cancer is less than natural and medical exposure.

The most severe nuclear accident is probably the Chernobyl disaster. In addition to conventional deaths and deaths of acute radiation syndrome, nine children die from thyroid cancer, and it is estimated that there are up to 4,000 cancer deaths among the approximately 600,000 people most exposed. Of the 100 million curies (4 exabecquerels) of radioactive material, short-lived radioactive isotopes such as 131 I Chernobyl released initially are the most dangerous. Because of their short half-life of 5 and 8 days they have now decayed, leaving the older 137 Cs (with a half-life of 30.07 years) and 90 Sr (with a half-life of 28, 78 years) as the main danger.

In March 2011, an earthquake and tsunami caused damage that caused explosions and partial leaks at the Fukushima Nuclear Power Plant in Japan. Significant release of radioactive material occurred after the hydrogen explosion at three reactors, when technicians tried to pump sea water to keep the uranium fuel rod cool, and mix the radioactive gas from the reactor to make room for the seawater. Concerns about a major release of radioactivity resulted in a 20 km exclusion zone set up around power plants and those within the 20-30 km zone are being advised to stay indoors. On March 24, 2011, Japanese officials announced that "radioactive iodine-131â €" beyond the safety limit for babies has been detected in 18 water purification plants in Tokyo and five other prefectures ".

Other serious radiation accidents include Kyshtym disaster (estimated 49 to 55 cancer deaths), and Windscale fires (an estimated 33 deaths from cancer).

Transit 5BN-3 SNAP 9A crash. On April 21, 1964, plutonium-containing satellites were burning in the atmosphere. Dr John Gofman claims it increases lung cancer rates worldwide. He said "While it is not possible to estimate the number of lung cancer caused by the accident, there is no question that the spread of so much Plutonium238 will increase the number of lung cancers diagnosed over the next few decades."

Maps Radiation-induced cancer



Mechanism

Cancer is a stochastic effect of radiation, which means that the likelihood of an increase in effective radiation dose, but the severity of the cancer is independent of the dose. The rate at which advanced cancer, prognosis, level of pain, and any other feature of the disease is not a function of the radiation dose in which the person is exposed. This contrasts with the deterministic effects of acute radiation syndromes that increase the severity with doses above the threshold. Cancer begins with a single cell whose operation is disrupted. Normal cell operations are controlled by the chemical structure of DNA molecules, also called chromosomes.

When radiation stores enough energy in organic tissues to cause ionization, it tends to break the bonds of molecules, and thus alters the molecular structure of the irradiated molecule. Less energetic radiation, like visible light, only causes excitation, not ionization, which is usually lost as heat with relatively little chemical damage. Ultraviolet light is usually categorized as non-ionizing, but is actually in the middle range that produces some ionization and chemical damage. Therefore the mechanism of carcinogenic ultraviolet radiation is similar to ionizing radiation.

Unlike chemical or physical triggers for cancer, radiation penetration strikes molecules in cells at random. The molecules that are broken down by radiation can become highly reactive free radicals that cause further chemical damage. Some of these direct and indirect damages will ultimately affect the chromosomes and epigenetic factors that control gene expression. Cellular mechanisms will correct some of these damages, but some improvements will go wrong and some chromosomal abnormalities will become irreversible.

DNA double-strand breaks (DSBs) are generally accepted as the most biologically significant lesions in which ionizing radiation causes cancer. In vitro experiments show that ionizing radiation causes DSBs at a rate of 35 DSB per cell per Gray, and removes some of the DNA epigenetic markers, which regulate gene expression. Most of the induced DSBs are repaired within 24 hours of exposure, however, 25% of the repaired strands are incorrectly repaired and about 20% of 200mGy-exposed fibroblast cells die within 4 days of exposure. Some of the population have defective DNA repair mechanisms, and thus suffer greater insult because of radiation exposure.

Major damage usually causes the cell to die or can not reproduce. This effect is responsible for acute radiation syndrome, but these severely damaged cells can not become cancerous. Lighter damage can leave a stable, functional cell that may be able to multiply and eventually develop into cancer, especially if the tumor suppressor gene is damaged. Recent research has shown that mutagenic events do not occur immediately after radiation. In contrast, surviving cells appear to have acquired genomic instability that causes mutations to increase in future generations. The cells will then develop through several stages of neoplastic transformation that may lead to tumors after years of incubation. Neoplastic transformation can be divided into three major independent stages: morphological changes in cells, cellular immortality acquisition (loss of normal and life-limiting regulatory processes), and adaptations that support tumor formation.

In some cases, small doses of radiation reduce the impact of subsequent larger radiation doses. This has been called an 'adaptive response' and is associated with the hypothetical mechanism of hormones.

The latent period of the decade can pass between radiation exposure and cancer detection. Cancers that may develop as a result of radiation exposure can not be distinguished from those occurring naturally or as a result of exposure to other carcinogens. Furthermore, the National Cancer Institute's literature suggests that chemical and physical hazards and lifestyle factors, such as smoking, alcohol consumption, and diet, significantly contribute to many of the same diseases. Evidence from uranium miners suggests that smoking may have a multiplication, not an additive, interaction with radiation. Evaluation of radiation contribution to cancer incidence can only be done through large epidemiological studies with comprehensive data on all other confusing risk factors.

Phytochemicals as modulators of ultraviolet-b radiation induced ...
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Skin cancer

Prolonged exposure to ultraviolet radiation from the sun can cause melanoma and other skin malignancies. Clear evidence establishes ultraviolet radiation, especially non-ionizing mid-wave UVB, as the cause of most non-melanoma skin cancers, which are the most common form of cancer in the world.

Skin cancer can occur after exposure to ionizing radiation following an average latent period of 20 to 40 years. A Chronic radiation keratosis is a precancerous keratotic skin lesion that may occur on the skin for years after exposure to ionizing radiation. Various malignancies can occur, most of the basal cell carcinoma frequency followed by squamous cell carcinoma. Increased risk is limited to radiation exposure sites. Several studies have also suggested a possible causal relationship between melanoma and exposure to ionizing radiation. Carcinogenic risk levels arising from low exposure levels are more controversial, but available evidence indicates an increased risk that is approximately proportional to the dose received. Radiologists and radiographers are among the earliest working groups exposed to radiation. That is the observation of the earliest radiologist who led to the introduction of radiation-induced skin cancer - the first solid cancer associated with radiation - in 1902. While secondary skin cancer incidents resulting from medication ionizing radiation were higher in the past, there is also some evidence that risk Certain cancers, especially skin cancers, can be increased among newer medical radiation workers, and these may be related to certain radiological practices or change. Existing evidence suggests that the excess risk of skin cancer lasts for 45 years or more after irradiation.

Frontiers | Adipose-Derived Stem Cells in Radiotherapy Injury: A ...
src: www.frontiersin.org


Epidemiology

Cancer is a stochastic effect of radiation, which means that it only has the possibility of occurrence, as opposed to the deterministic effect that always occurs at a certain dose threshold. The consensus of the nuclear industry, nuclear regulator, and government, is that the incidence of cancer from ionizing radiation can be modeled as linearly increasing with an effective radiation dose at 5.5% per sievert level. Individual studies, alternative models, and earlier versions of the industry consensus have resulted in other risk estimates scattered around this consensus model. There is general agreement that the risks are much higher for infants and fetuses than for adults, higher for middle-aged than elderly, and higher for women than men, although there is no quantitative consensus on this. This model is widely accepted for external radiation, but its application to internal contamination is disputed. For example, the model failed to account for low levels of cancer in early workers at Los Alamos National Laboratory exposed to plutonium dust, and high rates of thyroid cancer in children after Chernobyl accident, both of which were internal exposure events.. The European Committee on Radiation Risk calls the ICRP model "fatal defect" when it comes to internal exposure.

Radiation can cause cancer in most of the body, in all animals, and at any age, although radiation-induced solid tumors typically take 10-15 years, and may last up to 40 years, become clinically manifest, and radiation-induced leukemia usually takes 2-10 years to appear. Some people, such as those with nevoid basal cell syndrome or retinoblastoma basal syndrome, are more susceptible than the average to develop cancer from radiation exposure. Children and adolescents are twice as likely to develop leukemia from radiation as adults; radiation exposure before birth has ten times the effect.

Radiation exposure can cause cancer in all living tissues, but the full body-wide external exposure is most closely related to leukemia, which reflects high bone marrow radiosensitivity. Internal exposure tends to cause cancer in the organs where radioactive material concentrates, so radon mainly causes lung cancer, iodine-131 is most likely to cause thyroid cancer, etc.

Data source

The relationship between ionizing radiation exposure and cancer development is based primarily on the "LSS cohort" of victims of the Japanese atomic bomb, the largest human population ever exposed to high levels of ionizing radiation. However, the group is also exposed to high heat from both the light of the early infrared light and after the explosion due to their exposure to common fire storms and fires that flourished in both cities, resulting in victims also undergoing Hyperthermia therapy various degrees. Hyperthermia, or exposure to heat after radiation has been known in the field of radiation therapy to increase the severity of free radicals to cells after radiation. However, currently no effort has been made to meet this confounding factor, it is not included or corrected in the dose-response curve for this group.

Additional data has been collected from recipients of selected medical procedures and the Chernobyl disaster of 1986. There is a clear relationship (see UNSCEAR 2000 Report, Volume 2: Effects) between Chernobyl accident and an unusually large number, about 1,800, reported thyroid cancer in the area contaminated, mostly in children.

For low radiation levels, the biological effects are so small that they are undetectable in epidemiological studies. Although radiation can cause cancer at high doses and high doses, public health data on lower exposure levels, below about 10 mSv (1,000 mrem), is more difficult to interpret. To assess the health effects of lower radiation doses, researchers rely on a process model in which radiation causes cancer; several models that predict different levels of risk have emerged.

Studies of workers at work exposed to chronic low levels of radiation, above normal background, have provided mixed evidence on cancer and transgenerative effects. Cancer outcomes, though uncertain, are consistent with risk estimates based on atomic bomb victims and show that these workers face a slight increase in the likelihood of developing leukemia and other cancers. One of the latest and extensive worker studies was published by Cardis, et al. in 2005. There is evidence that low and low levels of radiation exposure is harmless.

Modeling

The linear dose-response model shows that each dose increase, no matter how small, results in a gradual increase in risk. The no-threshold model linear model (LNT) is accepted by the International Commission on Radiological Protection (ICRP) and regulators worldwide. According to this model, about 1% of the global population has cancer as a result of natural background radiation at some point in their lives. In comparison, 13% of deaths in 2008 were associated with cancer, so background radiation could make sense to be a small contributor.

Many criticize the application of ICRP to a linearly linear model to overestimate the effects of low radiation doses. The most commonly cited alternative is the "linear squared" model and the "hormesis" model. The linear squared model is widely seen in radiotherapy as the best model of cell survival, and it is the best for leukemia data from the LSS cohort.

In all three cases, alpha and beta values ​​should be determined by regression of human exposure data. Laboratory experiments on animals and tissue samples have limited value. Most of the high-quality human data available are of high dose individuals, above 0.1 Sv, so the use of models at low doses is extrapolated which may be under conservative or overly conservative. There is not enough human data available to resolve exactly which model is likely to be most accurate at low doses. Consensus has assumed linearly without threshold because it is the simplest and most conservative of the three.

Hormone radiation is the assumption that low ionizing radiation levels (ie, near the Earth's natural background radiation level) help "immunize" cells against DNA damage from other causes (such as free radicals or larger ionizing radiation doses), and decrease the risk of cancer. This theory proposes that low levels such as activating the body's DNA repair mechanism, cause higher levels of protein repair of DNA cells to be present in the body, enhancing the body's ability to repair DNA damage. This statement is very difficult to prove in humans (using, for example, statistical cancer studies) because the effects of very low ionizing radiation levels are too small to be measured statistically amid "noise" from normal cancer levels.

The idea of ​​a radiation hormone is considered unproven by the regulatory body. If the model of the hypothesis is accurate, it is conceivable that current rules based on the LNT model will prevent or limit the effects of hormones, and thus have a negative impact on health.

Other non-linear effects have been observed, especially for internal doses. For example, iodine-131 can be noted in high doses of isotopes sometimes less harm than low doses, as they tend to kill thyroid tissue which otherwise becomes cancer-induced by radiation. Most high-dose I-131 studies for the treatment of Grave's disease failed to find an increase in thyroid cancer, despite a linear increase in thyroid cancer risk with I-131 absorption at moderate doses.

Cancer Treatmentâ€
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Public security

Low-dose exposures, such as living near nuclear power plants or coal-fired power plants, which have higher emissions than nuclear plants, are generally believed to have little or no effect on cancer development, except for accidents. Greater attention includes radon in the building and overuse of medical imaging.

The International Commission on Radiological Protection (ICRP) recommends limiting community-made irradiation to an average of 1 mSv (0.001 Sv) effective dose per year, excluding medical and occupational exposure. For comparison, the level of radiation within the US House of Representatives is 0.85 mSv/year, close to the regulatory limit, due to the uranium content of the granite structure. According to the ICRP model, a person who spends 20 years inside a DPR building will have an additional one in thousands of possible cancers, over and above any other risk. (20 years X 0.85 mSv/year X 0.001 Sv/mSv X 5.5%/Sv = ~ 0.1%) That "risk exists" is much higher; the average American would have one in ten the chances of getting cancer during the same 20-year period, even without exposure to artificial radiation.

Internal contamination due to swallowing, inhalation, injection, or absorption is a special problem because the radioactive material can stay in the body for long periods of time, "doing" the subject to collect the old dose after the initial exposure has stopped, albeit at a low dose rate. More than a hundred people, including Eben Byers and radium girl, have received doses of more than 10 Gy and later die of cancer or natural causes, while the same number of acute external doses will always cause premature death by acute radiation. syndrome.

Public internal exposure is controlled by regulatory limits on radioactive content of food and water. These limits are usually expressed in becquerel/kilogram, with different limits set for each contaminant.

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History

Although radiation was discovered at the end of the 19th century, the dangers of radioactivity and radiation were not immediately recognized. The acute effect of radiation was first observed in the use of X-rays when Wilhelm RÃÆ'¶ntgen deliberately subjected his fingers to X-rays in 1895. He published his observations about developing burns, even though he attributed them to ozone rather than X-rays. The wounds healed later.

The genetic effects of radiation, including the effect on cancer risk, are acknowledged much later on. In 1927 Hermann Joseph Muller published a study that showed a genetic effect, and in 1946 was awarded the Nobel Prize for his findings. Radiation was soon associated with bone cancer in radium dial painter, but this was not confirmed until large-scale animal studies after World War II. The risk is then quantified through a long-term study of atomic bomb victims.

Before the biological effects of radiation were known, many doctors and companies began to market radioactive substances as patents and radioactive ingredients. An example is radium enema treatment, and water containing radium to be drunk as a tonic. Marie Curie speaks against such treatment, warning that the effects of radiation on the human body are not well understood. Curie later died of acute radiation syndrome, not cancer. Eben Byers, a famous American socialite, died of double cancer in 1932 after consuming large amounts of radium for several years; his death attracted public attention to the dangers of radiation. In the 1930s, after numerous cases of bone necrosis and death to fans, radium-containing medical products virtually disappeared from the market.

In the United States, an experience called Radium Girls, where thousands of radium-dial painter contracted mouth cancer, popularizing health warnings associated with radiation hazards. Robley D. Evans, at MIT, developed the first standard for permitted radium body weight, a key step in establishing nuclear medicine as a field of study. With the development of nuclear reactors and nuclear weapons in the 1940s, increasing scientific attention was given to the study of all kinds of radiation effects.

Accurate Assessment of Patient Effective Radiation Dose and ...
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Note


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References

Source of the article : Wikipedia

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