Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
51 Cards in this Set
- Front
- Back
BEIR V 1990 Committee on the Biological Effects of Radiation
|
Follow up of A-bomb survivors indicates that the number of excess cancers increase with age. This is in agreement with the relative risk model.
|
|
Estimates are still uncertain for A-bomb survivors. One reason is because the population exposed is just now entering the age where cancers are most prevalent.
|
There were about 76,000 survivors for whom dose estimates are available and who have been traced through 1985. However, almost half of these people received doses less than 0.5 rem.
|
|
Various studies on the survivors of Hiroshima and Nagasaki show that a population exposed to a dose of 12.5 Rem will have a measurable
|
increase about 1% in the incidence of cancer.
|
|
Note that the measurements are made on a population, not on individuals.
|
We can never say that a particular individual exposed to a particular dose of radiation will develop cancer.
|
|
BEIR V reported that the risk for solid tumors is 3 times larger than that reported in the BEIR III report
|
and 4 times larger for leukemias.
|
|
This change was mostly due to new dosimetry measurements which showed that the neutron component of the dose
|
was much smaller than previous estimates.
|
|
RBE for neutrons is high. So the result is that survivors received less
|
biologically effective dose than was previously estimated.
LESS ACTUAL DOSE CAUSING THE SAME OBSERVED HEALTH EFFECTS. |
|
According to BEIR V
|
If 100,000 people of all ages are exposed to 0.1 Gy or 10 rads in a single brief exposure, about 800 extra cancer deaths would be expected to occur during their remaining lifetimes.
|
|
According to BEIR V cont.
|
This is in addition to the 20,000 cancer deaths that would occur in the absence of the radiation.
|
|
According to BEIR V cont. 2
|
For all cancer other than leukemia, the study showed that under 4 Gray of exposure, the linear model for risk fit most closely. For leukemia, the linear quadratic model was more appropriate.
|
|
Using a linear model, how many extra deaths would be expected for the same population to 1 Rem of radiation?
|
80 extra cases
This result in an increase of 20000/20080 = 0.4% difficult to measure |
|
BEIR VI 1999 Committee on the Biological Effects of Radiation
|
This was the last BIER report to be published the National Research Council
|
|
BEIR VI 1999 Committee on the Biological Effects of Radiation cont.
|
The motivation for this report was not A-bomb survivors but the health effects of radon, specifically, lung cancers caused by radon and radon daughters in Private Homes
|
|
The study extrapolated data from miners, who receive on average a much larger dose than people do from household radon.
|
The study was also complicated by by other hazardous exposures common to miners.
|
|
Despite that radon is one of the most extensively studied carcinogens, the conclusion of the report is that it is inconclusive.
|
There is no definite answer regarding radon and lung cancer, probably because the risk is low. CIgarette smoke is for more dangerous by comparison.
|
|
The best estimate was that of the 11,000 lung caner deaths per year is non smokers, 2100 to 2900 are
|
radon related lung cancers
|
|
There is also evidence of a synergistic effect between radon and smoking. That is the two combined are more hazardous than each individually.
|
That is the two combined are more hazardous than each individually.
|
|
Local Tissue Damage - Early
|
Skin is a radiosensitive organ because it is a continually renewing system of cells. About 2% of skin cells are replaced each day. Damage to the basal cells of skin is most common as they are the most radioactive skin type cells,
|
|
A single dose of 100 to 300 rads can cause skin reddening called
|
erythema, which is similar to a sunburn. The erythema, appears in 1-2 days after irradiation. With an increased dose or moist desquamation will occur.
|
|
Radiation effects on the skin are a threshold effect. No effect is seen at low doses.
|
There is a minimum amount of radiation required about 50 rads before any effect is seen
|
|
Local Tissue Damage - Late
|
Late changes to skin from radiation include atrophy, fibrosis, changes in pigmentation, necrosis, ulceration and permanent depilation ( loss of hair.)
|
|
PICS
|
See P.P
|
|
A dose about 10 rads is required for any measurable change in humans. 10 rads can produce a measurable decrease in circulating
|
WBC, a decrease in the sperm count, and can suppress and delay menstruation in females.
|
|
Non-Specific Life Shortening ( Does Not Happen!!!)
|
Previous studies from the 50's and 60's showed that animals which were exposed to radiation insufficient to cause death, recovered but died sooner.
|
|
Additional studies have shown that at low doses, early death was due to
|
neoplasms (cancer)
|
|
Studies of humans, specifically A-bomb survivors who did not die from caner,
|
do not show acceleration of non-specific aging from radiation exposure.
|
|
Late Effects of Radiation: Genetic Changes
|
Radiation can effect the reproductive cells of humans, It does this in two ways:
|
|
1. With sufficient radiation, the cell will be killed.
|
2. If the cell is not killed, it may cause a hereditary change which can be carried to the next generation.
|
|
Male Sterility
Sperm Development |
Primary Spermatocytes -> secondary spermatocytes-> spermatids-> spermatoza
|
|
Radio-resistance increases with each cell type leading
|
to the mature spermatozoa (adult sperm cell)
|
|
Because of this, sterility from radiation exposure is delayed. The individual remains fertile until all the mature sperm are used up.
|
Stems cells are killed, so there are no cells to replace them.
|
|
Radiation Induced Sterility - Males
|
250 rads may cause temporary sterility in males lasting 1-2 years, but as little as 15 rads may cause temporary sterility.
|
|
Radiation Induced Sterility - Males cont.
|
350-600 rads acute exposure is enough to cause permanent sterility in males.
|
|
Female Sterility
|
Production of reproduction cells is different. There are no stem cells, but there are three types of immature eggs cells.
|
|
A dose of 50 rads
|
may cause temporary sterility in females.
|
|
A dose of at least 250 to 600 rads
|
can cause permanent sterility in females.
|
|
Radiation does not produce bizarre mutations!
|
Radiation produces an increase in the frequency of those mutations which occur spontaneously in any species.
|
|
No threshold for mutations:
|
Any amount of radiation carries some small risk of mutation
|
|
No threshold for mutations: cont
|
Most mutations whether spontaneous or induced by radiation are harmful to the organism.
|
|
aka epithalamus, secretes melantonin (circadian rhythms)
|
pineal gland-roof of the 3rd ventricle
|
|
Risk estimates developed from mouse experiments appear to be
|
similar to the genetic risk for humans.
|
|
Categorizing Mutations
Mendelian Diseases |
Caused by a single genetic mutation and show a simple predictable pattern.
|
|
Chromosomal Mutations
|
Are caused by gross abnormalities in he number of chromosomes i.e down's syndrome is caused by an extra chromosome 21
|
|
Categorizing Mutations
Multifactorial Diseases |
Describes the conditions which have a genetic component but not follow a simple mendelian patten.
Influenced by both genetics, environment & behavior. Ex. heart disease, diabetes, autism |
|
A parameter known as the doubling dose =
|
is used in genetic experiments. It is the amount of radiation required to produce twice the amount spontaneous mutations seen in the population.
|
|
The Mega Mouse Project
|
Used about 7 million mice to study the effects of radiation. Information on genetics defects comes almost entirely from animal studies.
|
|
Summary Findings
1. Different mutations have different radio sensitivities |
Radiosensitivity can differ by a factor of 35
|
|
2. There is a dose rate effect for mutations
|
in mice. Fewer mutation at low doses. At low doses the mutations rate in female reproductive cells is not above that of an un-irradiated mice.
|
|
3. Male Mice are more radiosenitive than females.
|
At a low dose rate, the male mice carries practically all of the burden of genetic mutation.
|
|
4. Genetic consequences following irradiation are reduced if there is
|
time between irradiation and conception. This may indicate a repair process. 6 months is the minimum recommended delay for humans.
|
|
5. BEIR V sys that the doubling doe for humans
|
is not likely to be less than 100 rem, estimated from mice,
The doubling dose for mice was found to be about 30 rads. |