7. RADIATION AND RADIATION PROTECTION
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7. RADIATION AND RADIATION PROTECTION. 7.3 BIOLOGICAL EFFECTS OF RADIATION AND RADIATION PROTECTION.

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7. RADIATION AND RADIATION PROTECTION

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7 radiation and radiation protection

7. RADIATION AND RADIATION PROTECTION

7.3 BIOLOGICAL EFFECTS OF RADIATION AND RADIATION PROTECTION

There is no direct evidence of radiation-induced genetic effects in humans, even at high doses. Various analyses indicate that the rate of genetic disorders produced in humans is expected to be extremely low, on the order of a few disorders per million live born per rem of parental exposure. 


7 radiation and radiation protection

quality of radiation

quantity of radiation

received dose of radiation

exposure conditions (spatial distribution)

The potential biological effects and damages caused by radiation depend on the conditions of the radiation exposure.

It is determined by:

The different kinds of radiation have different energy loss effects LET.


7 radiation and radiation protection

Energy loss effects depends on nature and probability of interaction

between radiation particle and body material.

Particles with high energy loss effects cause typically greater damage.

To normalize these effects as an empirical parameter the RelativeBiologicalEffectiveness RBE of radiation for producing a given biological effect is introduced:

The RBE for different kinds of radiation can be expressed in terms of

energy loss effects LET.


7 radiation and radiation protection

For low LET radiation,  RBE  LET, for higher LET the RBE increases to a maximum, the subsequent drop is caused by the overkill effect.

These high energies are sufficient to kill more cells than actually available!


7 radiation and radiation protection

Radiation damage to body organs, tissue, and cells is a purely statistical effect

As higher the radiation dose as more likely some effects will occur. As higher the LETand/or the RBEas more likely damage may occur. The effects are typically described by empirical dose-responsecurves.

Schematic representation of dose-response function E(D) at low doses D for high-LET (curve H) and low-LET (curve L1,) radiations. L2is the extension of the linear beginning of L1.


7 radiation and radiation protection

Radiation can cause immediate effects (radiation sickness), but also long term effects which may occur many years (cancer) or several generations later (genetic effects).

Biological effects of radiation result from both direct and indirect action of radiation.

Direct action is based on direct interaction between radiation particles and complex body cell molecules, (for example direct break-up of DNA molecules)


7 radiation and radiation protection

  • Radiation deposits energy into the body tissue by energy loss effects

compton scattering, photo-excitation for g- and X-rays

scattering and ionization processes for a-, p, n-particles (LET)

  • Energy loss causes ionization and break-up of simple body molecules:

H2O  H+ + OH

Indirect action is more complex and depends heavily on the energy loss effects of radiation in the body tissue and the subsequent chemistry.

  • OH radical attacks DNA-molecule.

  • Resulting biological damage depends on the kind of alteration andcan cause cancer or long-term genetic alterations.


7 radiation and radiation protection

RADIATION

DIRECT IONIZATION

OF DNA

IONIZATION OF

OTHER MOLECULES, e.g.,H2O

radiation + H2O  H2O+ + e

H2O+ H+ + OH0

e + H2O  H0 + OH

OXIDATION OF DNA

BY OH RADICALS

CHEMICAL

RESTORATION

ENZYMATIC REPAIR

NO EFFECT

DNA

RESTORED

PERMANENT DAMAGE IN DNA

BIOLOGICAL EFFECTS

1. GENETIC EFFECTS

2. SOMATIC EFFECTS

CANCER

STERILITY


7 radiation and radiation protection

The time scales for the short and long term effects of radiation are symbolized in the figure and listed in the table


7 radiation and radiation protection

survivors of the atomic bomb detonations at Hiroshima and Nagasaki

medical exposure to patients (in particular in the early forties and fifties)

evaluations of populations with high occupational exposure

evaluations of populations with high radiation background (high altitude)

There are many biological effects a high dose of radiation can cause:

The results are based on several data sources on radiation exposure to humans


7 radiation and radiation protection

Skin Effects

The first evidence of biological effects of radiation exposure appears on the exposed skin.

The different stages depend on the dose and on the location of the exposure.


7 radiation and radiation protection

Acute Radiation Syndrome

The body consists of cells of different radiation sensitivity, a large dose of radiation delivered acutely does larger damage than the same does delivered over a long period of time.

The body response to a large acute dose manifests itself in the acuteradiation syndrome.


7 radiation and radiation protection

The first (prodomal) symptoms show up after  6 hours

These symptoms subside during the latent period, which lasts between one (high doses) and four weeks (low doses) and is considered an incubation period during which the organ damage is progressing

The latent period ends with the onset of the clinical expression of the biological damage, the manifest illness stage, which lasts two to three weeks

Survival of the manifest illness stage practically guaranties full recovery of the patient


7 radiation and radiation protection

The severity and the timescale for the acute radiation syndrome

depends on the maximum delivered dose.

The first symptoms show up after  6 hours

If the whole body exposure exceeds a critical threshold rate of 50 -100 rad the symptoms show up more rapidly and drastically.


7 radiation and radiation protection

Long term radiation risks are more difficult to assess. The predictions are based on the use of risk models.

The main problem are the insufficient statistical long term data about radiation victims which make reliable model predictions difficult.


7 radiation and radiation protection

In particular for low LET exposure linear and quadratic dose-response models differ considerably in their risk assessment


7 radiation and radiation protection

The risk assessment depends on the age of the exposed person, different organs have a different response to radiation, therefore the risk of cancer differs considerably.


7 radiation and radiation protection

The total lifetime detriment incurred each year from radiation by a worker exposed to the limits over his/her lifetime should be no greater than the annual risk of accidental death in a " safe" industry

environment.

Annual rate of fatal accidents ranges from 0.2104 (service industries) to 5104 (min in industries).

For an averaged measured effective dose of 2.1 mSv for radiation workers, the total detriment to receive radiation damage is:

21 103 Sv/y  4.0 102 Sv1 = 8.4 104y1 0.001 y1

This level is in the range of the average annual risk for accidental death for all industries.


7 radiation and radiation protection

To control the distribution of exposure over a working career theannual effective doseis limited to 50 mSv(not including medical and natural background exposure)

To account for the cumulative effects of radiation, an age-dependent limit of 10 mSv • age (y) is introduced.

Workers at age of 64 at the end of their career with an accumulated effective dose of 640 mSv would have a lifetime detriment of:

0.64Sv • 4.0•10-2Sv-1 = 2.6•10-2

in comparison their lifetime risk of a fatal accident over their 50 y working career is of comparable order:

50y • 5.0•10-4y-1 = 2.5•10-2

For specific organs special limits for the annual equivalent dose are recommended.


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