Radiobiology

Source: Wikipedia, the free encyclopedia.

Radiobiology (also known as radiation biology, and uncommonly as actinobiology) is a field of clinical and basic

radiotherapy
.

Health effects

In general, ionizing radiation is harmful and potentially lethal to living beings but can have health benefits in

thyrotoxicosis
.

Most adverse health effects of radiation exposure may be grouped in two general categories:

  • deterministic effects (harmful tissue reactions) due in large part to the killing or malfunction of cells following high doses; and
  • stochastic effects, i.e., cancer and heritable effects involving either cancer development in exposed individuals owing to mutation of somatic cells or heritable disease in their offspring owing to mutation of reproductive (germ) cells.[1]

Stochastic

Some effects of ionizing radiation on human health are

heart disease
are all stochastic effects induced by ionizing radiation.

Its most common impact is the stochastic

effective radiation dose at a rate of 5.5% per sievert.[3] If this linear model is correct, then natural background radiation
is the most hazardous source of radiation to general public health, followed by medical imaging as a close second.

Quantitative data on the effects of ionizing radiation on human health is relatively limited compared to other medical conditions because of the low number of cases to date, and because of the stochastic nature of some of the effects. Stochastic effects can only be measured through large epidemiological studies where enough data has been collected to remove confounding factors such as smoking habits and other lifestyle factors. The richest source of high-quality data comes from the study of Japanese

atomic bomb survivors. In vitro and animal experiments are informative, but radioresistance
varies greatly across species.

The added lifetime risk of developing cancer by a single abdominal CT of 8 mSv is estimated to be 0.05%, or 1 in 2,000.[4]

Deterministic

Further information: Acute radiation syndrome

Deterministic effects are those that reliably occur above a threshold dose, and their severity increases with dose.[2]

High radiation dose gives rise to deterministic effects which reliably occur above a threshold, and their severity increases with dose. Deterministic effects are not necessarily more or less serious than stochastic effects; either can ultimately lead to a temporary nuisance or a fatality. Examples of deterministic effects are:

The US National Academy of Sciences Biological Effects of Ionizing Radiation Committee "has concluded that there is no compelling evidence to indicate a dose threshold below which the risk of tumor induction is zero".[5]

Phase Symptom Whole-body absorbed dose (Gy)
1–2 Gy 2–6 Gy 6–8 Gy 8–30 Gy > 30 Gy
Immediate Nausea and vomiting 5–50% 50–100% 75–100% 90–100% 100%
Time of onset 2–6 h 1–2 h 10–60 min < 10 min Minutes
Duration < 24 h 24–48 h < 48 h < 48 h — (patients die in < 48 h)
Diarrhea None None to mild (< 10%) Heavy (> 10%) Heavy (> 95%) Heavy (100%)
Time of onset — 3–8 h 1–3 h < 1 h < 1 h
Headache Slight Mild to moderate (50%) Moderate (80%) Severe (80–90%) Severe (100%)
Time of onset — 4–24 h 3–4 h 1–2 h < 1 h
Fever None Moderate increase (10–100%) Moderate to severe (100%) Severe (100%) Severe (100%)
Time of onset — 1–3 h < 1 h < 1 h < 1 h
CNS function No impairment Cognitive impairment 6–20 h Cognitive impairment > 24 h Rapid incapacitation
Seizures, tremor, ataxia, lethargy
Latent period
 28–31 days 7–28 days < 7 days None None
Illness
 Mild to moderate
Fatigue
Weakness
 Moderate to severe
Infections
Alopecia after 3 Gy
 Severe
Electrolyte disturbance
 Nausea
Vomiting
Severe diarrhea
High fever
Electrolyte disturbance
Shock 		— (patients die in < 48h)
Mortality Without care 0–5% 5–95% 95–100% 100% 100%
With care 0–5% 5–50% 50–100% 99–100% 100%
Death 6–8 weeks 4–6 weeks 2–4 weeks 2 days – 2 weeks 1–2 days
Table source[6]

By type of radiation

When alpha particle emitting isotopes are ingested, they are far more dangerous than their half-life or decay rate would suggest. This is due to the high

actinides
are an average of about 20 times more dangerous, and in some experiments up to 1000 times more dangerous than an equivalent activity of beta emitting or gamma emitting radioisotopes. If the radiation type is not known, it can be determined by differential measurements in the presence of electrical fields, magnetic fields, or with varying amounts of shielding.

External dose quantities used in radiation protection. See article on sievert on how these are calculated and used.

In pregnancy

The risk for developing radiation-induced cancer at some point in life is greater when exposing a fetus than an adult, both because the cells are more vulnerable when they are growing, and because there is much longer lifespan after the dose to develop cancer. If there is too much radiation exposure there could be harmful effects on the unborn child or reproductive organs.[7] Research shows that scanning more than once in nine months can harm the unborn child.[8]

Possible deterministic effects include of radiation exposure in pregnancy include miscarriage, structural birth defects, growth restriction and intellectual disability.[9] The deterministic effects have been studied at for example survivors of the atomic bombings of Hiroshima and Nagasaki and cases where radiation therapy has been necessary during pregnancy:

Gestational age
Embryonic age
 Effects Estimated threshold dose (mGy)
2 to 4 weeks 0 to 2 weeks Miscarriage or none (all or nothing) 50 - 100[9]
4 to 10 weeks 2 to 8 weeks Structural birth defects 200[9]
Growth restriction 200 - 250[9]
10 to 17 weeks 8 to 15 weeks Severe intellectual disability 60 - 310[9]
18 to 27 weeks 16 to 25 weeks Severe intellectual disability (lower risk) 250 - 280[9]

The intellectual deficit has been estimated to be about 25 IQ points per 1,000 mGy at 10 to 17 weeks of gestational age.[9]

These effects are sometimes relevant when deciding about medical imaging in pregnancy, since projectional radiography and CT scanning exposes the fetus to radiation.

Also, the risk for the mother of later acquiring radiation-induced breast cancer seems to be particularly high for radiation doses during pregnancy.[10]

Measurement

The human body cannot sense ionizing radiation except in very high doses, but the effects of ionization can be used to characterize the radiation. Parameters of interest include disintegration rate, particle flux, particle type, beam energy, kerma, dose rate, and radiation dose.

The monitoring and calculation of doses to safeguard human health is called dosimetry and is undertaken within the science of health physics. Key measurement tools are the use of dosimeters to give the external effective dose uptake and the use of bio-assay for ingested dose. The article on the sievert summarises the recommendations of the ICRU and ICRP on the use of dose quantities and includes a guide to the effects of ionizing radiation as measured in sieverts, and gives examples of approximate figures of dose uptake in certain situations.

The committed dose is a measure of the stochastic health risk due to an intake of radioactive material into the human body. The ICRP states "For internal exposure, committed effective doses are generally determined from an assessment of the intakes of radionuclides from bioassay measurements or other quantities. The radiation dose is determined from the intake using recommended dose coefficients".[11]

Absorbed, equivalent and effective dose

The

rad
is sometimes also used, predominantly in the USA.

To represent stochastic risk the

International Committee on Radiation Protection (ICRP) and International Commission on Radiation Units and Measurements
(ICRU). The coherent system of radiological protection quantities developed by them is shown in the accompanying diagram.

Organizations

The International Commission on Radiological Protection (ICRP) manages the International System of Radiological Protection, which sets recommended limits for dose uptake. Dose values may represent absorbed, equivalent, effective, or committed dose.

Other important organizations studying the topic include

Exposure pathways

External

A schematic diagram showing a rectangle being irradiated by an external source (in red) of radiation (shown in yellow)
A schematic diagram showing a rectangle being irradiated by radioactive contamination (shown in red) which is present on an external surface such as the skin; this emits radiation (shown in yellow), which can enter the animal's body

External exposure is exposure which occurs when the radioactive source (or other radiation source) is outside (and remains outside) the organism which is exposed. Examples of external exposure include:

External exposure is relatively easy to estimate, and the irradiated organism does not become radioactive, except for a case where the radiation is an intense neutron beam which causes activation.

By type of medical imaging

Effective dose by medical imaging type
Target organs Exam type Effective dose in adults[14] Equivalent time of background radiation[14]
CT of the head Single series 2 mSv 8 months
With + without
radiocontrast
 4 mSv 16 months
Chest CT of the chest 7 mSv 2 years
CT of the chest, lung cancer screening protocol 1.5 mSv 6 months
Chest X-ray 0.1 mSv 10 days
Heart Coronary CT angiography 12 mSv 4 years
Coronary CT calcium scan 3 mSv 1 year
Abdominal CT of abdomen and pelvis 10 mSv 3 years
CT of abdomen and pelvis, low dose protocol 3 mSv[15] 1 year
CT of abdomen and pelvis, with + without
radiocontrast
 20 mSv 7 years
CT Colonography 6 mSv 2 years
Intravenous pyelogram
 3 mSv 1 year
Upper gastrointestinal series 6 mSv 2 years
Lower gastrointestinal series 8 mSv 3 years
Spine Spine X-ray 1.5 mSv 6 months
CT of the spine 6 mSv 2 years
Extremities X-ray of extremity 0.001 mSv 3 hours
Lower extremity
CT angiography
 0.3 - 1.6 mSv[16] 5 weeks - 6 months
Dental X-ray 0.005 mSv 1 day
DEXA (bone density) 0.001 mSv 3 hours
PET-CT combination 25 mSv 8 years
Mammography 0.4 mSv 7 weeks

Internal

Internal exposure occurs when the radioactive material enters the organism, and the radioactive atoms become incorporated into the organism. This can occur through inhalation, ingestion, or injection. Below are a series of examples of internal exposure.

When radioactive compounds enter the human body, the effects are different from those resulting from exposure to an external radiation source. Especially in the case of alpha radiation, which normally does not penetrate the skin, the exposure can be much more damaging after ingestion or inhalation. The radiation exposure is normally expressed as a committed dose.

History

Although radiation was discovered in late 19th century, the dangers of radioactivity and of radiation were not immediately recognized. Acute effects of radiation were first observed in the use of

free radical
produced in air by X-rays. Other free radicals produced within the body are now understood to be more important. His injuries healed later.

As a field of medical sciences, radiobiology originated from

Ivan Romanovich Tarkhanov concluded that these newly discovered rays not only photograph, but also "affect the living function".[18] At the same time, Pierre and Marie Curie discovered the radioactive polonium and radium later used to treat cancer
.

The genetic effects of radiation, including the effects on cancer risk, were recognized much later. In 1927

Nobel prize
for his findings.

More generally, the 1930s saw attempts to develop a general model for radiobiology. Notable here was Douglas Lea,[19][20] whose presentation also included an exhaustive review of some 400 supporting publications.[21][page needed][22]

Before the biological effects of radiation were known, many physicians and corporations had begun marketing radioactive substances as patent medicine and radioactive quackery. Examples were radium enema treatments, and radium-containing waters to be drunk as tonics. Marie Curie spoke out against this sort of treatment, warning that the effects of radiation on the human body were not well understood. Curie later died of aplastic anemia caused by radiation poisoning. Eben Byers, a famous American socialite, died of multiple cancers (but not acute radiation syndrome) in 1932 after consuming large quantities of radium over several years; his death drew public attention to dangers of radiation. By the 1930s, after a number of cases of bone necrosis and death in enthusiasts, radium-containing medical products had nearly vanished from the market.

In the United States, the experience of the so-called

MIT, developed the first standard for permissible body burden of radium, a key step in the establishment of nuclear medicine as a field of study. With the development of nuclear reactors and nuclear weapons
in the 1940s, heightened scientific attention was given to the study of all manner of radiation effects.

The atomic bombings of Hiroshima and Nagasaki resulted in a large number of incidents of radiation poisoning, allowing for greater insight into its symptoms and dangers. Red Cross Hospital surgeon Dr. Terufumi Sasaki led intensive research into the Syndrome in the weeks and months following the Hiroshima bombings. Sasaki and his team were able to monitor the effects of radiation in patients of varying proximities to the blast itself, leading to the establishment of three recorded stages of the syndrome. Within 25–30 days of the explosion, the Red Cross surgeon noticed a sharp drop in white blood cell count and established this drop, along with symptoms of fever, as prognostic standards for Acute Radiation Syndrome.[25] Actress Midori Naka, who was present during the atomic bombing of Hiroshima, was the first incident of radiation poisoning to be extensively studied. Her death on August 24, 1945, was the first death ever to be officially certified as a result of radiation poisoning (or "atomic bomb disease").

The Atomic Bomb Casualty Commission and the Radiation Effects Research Foundation have been monitoring the health status of the survivors and their descendants since 1946. They have found that radiation exposure increases cancer risk, but also that the average lifespan of survivors was reduced by only a few months compared to those not exposed to radiation. No health effects of any sort have thus far been detected in children of the survivors.[26]

Areas of interest

The interactions between organisms and electromagnetic fields (EMF) and ionizing radiation can be studied in a number of ways:

Radiation sources for experimental radiobiology

Radiobiology experiments typically make use of a radiation source which could be:

See also

References

  1. ^ ICRP 2007, p. 49, paragraph 55.
  2. ^
    PMID 24275177
    .Note: first page available free at URL.
  3. ^ ICRP 2007, p. 55, Paragraph 83.
  4. ^ "Do CT scans cause cancer?". Harvard Health Publishing. Harvard University. March 2013. Retrieved 15 Jul 2020. Note: First paragraph provided free.
  5. ISBN 978-0-309-09156-5
    . Retrieved 11 Nov 2013.
  6. ^ "Radiation Exposure and Contamination - Injuries; Poisoning - Merck Manuals Professional Edition". Merck Manuals Professional Edition. Retrieved 6 Sep 2017.
  7. PMID 19047611
    .
  8. PMID 19047611
    .
  9. ^
    American Congress of Obstetricians and Gynecologists
    . February 2016
  10. PMID 15642178
    .
  11. ^ ICRP 2007, p. 73, paragraph 144.
  12. ^ ICRP 2007, p. 24, glossary.
  13. ^ ICRP 2007, pp. 61–62, paragraphs 104 and 105.
  14. ^
    RadiologyInfo.org by Radiological Society of North America
    . Retrieved 23 Oct 2017.
  15. PMID 27578040
    .
  16. PMID 24915439
    .
  17. PMID 11749482
    .
  18. ISBN 9781600212802
    . Page xxi.
  19. S2CID 250827449
    .
  20. ^ Lea, Douglas E. "Radiobiology in the 1940s". British Institute of Radiology. Retrieved 15 Jul 2020.
  21. ISBN 9781001281377
    .
  22. PMC 1932419
    .
  23. ^ Grady, Denise (6 October 1998). "A Glow in the Dark, and a Lesson in Scientific Peril". The New York Times. Retrieved 25 Nov 2009.
  24. OSTI 751062
    . Retrieved 24 May 2012.
  25. ISBN 978-0-88363-991-7
    .
  26. ^ "Long-term health effects of Hiroshima and Nagasaki atomic bombs not as dire as perceived". Science Daily. 11 August 2016. Retrieved 16 Oct 2021.
  27. S2CID 8711325. Archived from the original
    (PDF) on 16 Jul 2020.

Sources

Further reading

Look up radiobiology, radiation biology, or actinobiology in Wiktionary, the free dictionary.
  • Eric Hall, Radiobiology for the Radiologist. 2006. Lippincott
  • G.Gordon Steel, "Basic Clinical Radiobiology". 2002. Hodder Arnold.
  • The Institute for Radiation Biology at the Helmholtz-Center for Environmental Health [1]
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