Stochastic Effects and Late Tissue Reactions of Radiation in organ systems Chapter 9 Radiation Safety

Radiation damage at the cellular level may lead to measurable ____________ or ________________________ in the living organism as whole further on in life

somatic or hereditary damage

__________________ are the long term results of radiation exposure

Late effects

Examples of late effects:

-

-

-

Cataracts

Leukemia

Genetic mutations

______________ are a late tissue reaction that is non-random

Cataracts

___________ and _____________________are stochastic or random consequences and if they appear they do not do so for an extended period of time

Leukemia and genetic mutations

Late effects occur how long after irradiation?

months to years after irradiation

is defined as a science that deals with the incidence. Distribution, and control of disease in a population

Epidemiology

These studies are significant to radiobiologist who use the information from these studies to formulate dose response estimates for making predictions of the risk of cancer in human populations exposed to

low doses of ionizing radiation

is demonstrated graphically through a curve (DR curve) that maps the observed effects of radiation exposure in relation to the dose of radiation received

The radiation dose response relationship

The effect may be the incidence of disease or may be the

severity of an effect

Dose Response curve is either:

-

-

-

-

Linear (straight line)

Non linear (curved to some degree

Threshold dose

Non-threshold dose

may be defined as a point or level at which a response or reaction to an increasing stimulation first occurs

Threshold

means that below certain absorbed radiation dose no biologic effect will happen, once that dose is reached the effect will appear

Reference to radiation

indicated that a radiation absorbed dose of any magnitude has the capability of producing biologic effect

Non-threshold

will be caused by radiation all the way down to zero on the graph

Biologic effect response

(T/F) Any amount of dose can cause biologic effect

TRUE

means there is a direct proportion relation between the amount of dose and the biologic effect or disease in question

Linear

As dose goes up the

severity of or the chance of disease goes up

proclaim that no radiation dose is considered absolutely safe and with the severity of the biologic effect increasing directly with the magnitude of the absorbed dose

Linear, non-threshold relationships

means that there is no direct proportion relationship between dose and observed effect

Non-linear

1980 BEIR report concluded that most stochastic effects (cancer) and hereditary effects at low dose LET radiation levels appear to follow a

linear quadratic non-threshold dose response curve

implies that the equation that best fits the information has components that depend on dose to the first power (linear) and dose that is squared (quadratic)

Linear quadratic

Newer models have been come out since 1980

...

1990 report indicated risk was about _________________ than previously projected

3-4 times greater

Currently the committee recommends the use of the _________________________________ of radiation dose response for most types of cancer

linear nonthreshold curve

With the _________________ if the absorbed dose is doubled the biologic response probability and actual occurrence in large population samples is also doubled

LNT

The 1990 committee saw the _________________ curve that was previously used to fit better with stochastic and genetic effects at low dose levels from low LET radiation

LQNT

The following are presumed to follow the LQNT curve:

-

-

-

Leukemia

Breast cancer

Heritable damage

Continued use of the __________________________ model for radiation protection standards has the potential to exaggerate the seriousness of radiation effects at lower dose levels

linear dose response

Research continues to see if this can be changed

...

In establishing these standards the regulatory agencies have chosen to be conservative They use a model that may overestimate the risk at low doses but is not expected to

underestimate the risk

Acute reactions like skin erythema and hematologic depression may be demonstrated on

linear threshold dose response curve

what does not occur below a certain dose?

Biologic response

What is generally used for radiation at high doses - usually used in radiation therapy

sigmoid or s-shaped (nonlinear) threshold curve

when living organisms that have been exposed to radiation sustain biologic damage

Somatic effects

Effects occur in the individual that was exposed

Somatic Effects

Somatic Effects Subdivided into two categories:

-

-

Stochastic Effects

Tissue Reactions

Probability that the effect happens depends on the received dose, but severity of the effect does not

Stochastic effects

Example of Stochastic effects

Cancer

Both the probability and the severity of the effect depend on the dose

Tissue Reactions

Consequences of radiation exposure months or years afterwards

Late somatic effects

Can be stochastic or tissue reactions

Late somatic effects

Stochastic effects like cancer can take how long to see?

Years

Tissue reactions are usually a little sooner but still may take

months or more for full expression

are the result of slowly developing changes to the body tissue that may be modified by other factors after exposure (medical intervention)

Tissue reactions

are generally determined at the time of irradiation

Stochastic effects

is a consideration for patients and personnel exposed from imaging procedures

Low level dose

(T/F)Risk for developing cancer is still controversial

TRUE

There is no conclusive proof that low LET ionizing radiation absorbed at doses below__________ cause significant increase in risk of cancer

0.1 Gy

(T/F) Risk may be negligible or maybe even nonexistent

TRUE

Sources of low level radiation exposure include:

-

-

-

-

-X-rays

-Radioactive materials used for diagnostic purposes

-Employment related exposures in medicine

-Natural background exposure

Low level low LET radiation dose has been defined as absorbed dose of ___________ or less delivered over a short period of time

Or as a larger dose over long period of time

0.1 Sv

Three categories of harmful health consequences for developing cancer from low level radiation exposure

-

-

-

-Cancer induction

-Damage to the unborn from irradiation in utero

-Genetic effects

Three major types of late effects

-

-

-

-Carcinogenesis - stochastic

-Cataractogenesis - late tissue reaction

-Embryologic effects (birth defects) - stochastic

Risk estimates to predict cancer may be given in terms of

-

-

absolute risk or

relative risk

Both models forecast the number of excess cancer or cancers that would not have occurred in the population in question without the exposure to ionizing radiation

absolute risk or relative risk

forecast that a specific number of malignancies will occur as a result of the exposure

Absolute risk

predicts that the number of excess cancers will increase as the natural incidence of cancer increases with advancing age in a population

Relative risk

Predicts the percentage increase in incidence rather than the specific number of cases

More recent studies support this

relative risk

means a cancer producing substance

Carcinogenic

Example of a carcinogenic

Radiation

is the most important late stochastic effect caused by exposure to ionizing radiation

Cancer

(T/F) Random occurrence

TRUE

(T/F) does not have a threshold

TRUE

(T/F) the severity of the disease is not dose related

TRUE

(T/F) Studies have proven that radiation does not induce cancer

FALSE it does induce

Cancer from natural causes occurs frequently and the number of cancers induced by radiation is small in comparison to cancer from

low level radiation is hard to identify

In 1920s-1930s women hand painted numerals on watches and clocks with

radium containing paint

For the fine details some would place the brush to their lips to draw the bristles to a fine point - leading to

ingestion of a large amount of radium

Accumulation of radium in their body caused:

-

-

-

-Development of osteoporosis -

-Osteogenic sarcoma -

-Other cancers of the epithelial cells of the nasopharynx and paranasal sinuses

decalcification of the bone

osteoporosis

bone cancer

Osteogenic sarcoma

is a radioactive material with very long half life

Uranium 4.5 billion years

Emits alpha, beta, and gamma radiation as it decays

Radon is part of the decay family

of uranium Decay

Uranium Miners inhaled significant amounts of

radon

This lead to about 50% of the miners succumbing to

lung cancer

Also in the United States miners during the Cold War worked without regulated working conditions in mines breathing in

radioactive dust and drinking radioactive water

Estimated these miners got about ___________ or more

10 Sv

(T/F) Families were also exposed because of the dust on the clothing of the miners

TRUE

early radiation workers developed

cancerous skin lesions

When compared to non-radiation working counterparts a significant number also had higher incidence of:

-

-

Aplastic anemia

Leukemia

Estimated may have received how much dose per year

1Gy/yr

(T/F) Now with all the radiation protection and safety standards consequences like these are not experienced

TRUE

Studies show that workers after the 1940s had no increase in

adverse health effects

Used between 1925-1945 for angiography

contrast agent thorotrast

contrast agent thorotrast Emitted _________________ when injected

alpha particles

contrast agent thorotrast _____________ and____________ primary recipients of agent

Liver and spleen

After about 15-20 years resulted in many cases of:

-

-

-

-

Liver cancer

Spleen cancer

Angiosarcomas

Biliary duct carcinomas

During 1940s-early 1950s to reduce the size of the thymus gland physicians treated infants with

therapeutic doses (1.2-60Gy) of x-radiation

Thyroid received substantial dose

...

Resulted in development some 20 years later of

thyroid nodules and carcinomas in many of the treated infants

patients treated with radiation breast cancer incidence doubled from 3.2% expected to 6.3% actual - there is a lot of study on if mammo for screening could cause breast cancer development

Postpartum mastitis

Children of the Marshall Island atomic bomb testing developed

thyroid cancer

Japanese atomic bomb survivors - some still being observed- have found:

-

-

-

-

-

Increased incidence of leukemia

Thyroid cancer

Breast cancer

Lung cancer

Bone cancers

Studies show that only an excess of ______cancer deaths attributed to radiation exposure

250

Instead of the expected 4500 deaths, 4750 actually occurred

...

Meaning about every 300 atomic bomb survivors 1 died of a malignancy attributed to radiation dose

...

Radiation induced leukemia Follows a what dose relationship

linear relationship with dose

Chance on developing leukemia is ___________________ to the magnitude of radiation exposure

directly proportional

Radiation induced leukemia Data has not indicated

threshold type relationship