Radiation Biology: Ch. 9

science that deals with the incidence, distribution, and control of disease in a population

epidemiology

what does epidemiology compare

incidence of disease within groups of people

ex: radiation induced cancer vs. natural incidence in the human population

the formation of cancer

carcinogenesis “tumorigenesis”

what is cancer defined as

disease in which healthy cells have been transformed into nonstandard cells that divide uncontrollably

graphic representation that maps the observed effects of radiation exposure in relation to the dose of radiation received

radiation dose-response relationship (DR curve)

types of DR curves

linear or non-linear

threshold or non threshold

implies biologic response to radiation is directly proportional to the dose received

linear relationship, straight line

what is each line on this graph

1. linear non threshold

2. linear threshold

3. non linear threshold

curved to some degree, can be threshold or non threshold

non linear

what is a Sigmoid or S-shaped curve generally employed in

radiation therapy to demonstrate high dose, dose cellular response

is the point at which a response or reaction first occurs, below this level nothing occurs

graph begins at some point after 0

threshold

what does a linear non-threshold graph mean

some biological effects are caused in living organisms by even the smallest doses of ionizing radiation

what type of graph are radiation protection standards based on

linear non threshold (LNT)

two types of models- one for high dose exposure and one for low dose exposure

linear and linear-quadratic

fits both high and low dose data, may overestimate the risk of low doses

linear model

shows that no biologic response curve occurs below a specific dose level

linear threshold

what does linear quadratic mean

the data depends on a dose to the 1st power and also on dose squared

what does the BEIR committee recommend the linear quadratic model for

leukemia only

what is this curve representing

linear quadratic

which type of graph does the committee recommend for most types of cancers

linear non threshold

used for leukemia, breast cancer, heritable damage

more conservative dose response outcome for low level radiation

linear quadratic non threshold dose response

what are somatic effects

biological damage to living organism after being exposed to radiation

two classifications of somatic effects

• stochastic

• tissue reactions

in tissue reactions, what does both probability and severity depend on

the dose received

radiation induced damage at the cellular level may lead to measurable somatic and hereditary damage in the living organism or later on in life

late somatic effects

examples of late tissue reactions

• cataract formation

• fibrosis

• organ atrophy

• loss of parenchymal cells

• reduced fertility

• sterility

examples of stochastic effects

• cancer

• genetic effects

what has low level radiation dosage been defined as

equivalent dose of 0.1 Sv or less delivered over a short time and larger dose delivered over a long time

3 categories of consequences also require study at low dose levels, concluded by scientific committees

• cancer induction

• damage to unborn from irradiation in utero

• genetic effects

3 major types of late effects

1. carcinogenesis (late stochastic)

2. cataractogenous (late tissue)

3. embryologic effects (late stochastic)

predicts cancer incidence in terms of absolute risk or relative risk

risk models

model that forecasts that a specific number of malignancies will occur as a result of exposure

absolute risk model

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

relative risk model

types of radiation induced cancers

• bone cancer

• leukemia

• skin cancer

• breast cancer

• lung cancer

• thyroid cancer

how was bone cancer received in the 1920’s and 1930’s

radium watch dial painters-radium incorporated into bone tissue because of being chemically similar to calcium

which bones were most affected by bone cancer

mandible, pelvis, femur

what other malignancies did radium watch dial painters receive

carcinoma of the epithelial cells lining the nasopharynx and sinuses

how much dose were watch dial painters assumed to have received

5Gyt

in the early years of last century, how did many die from lung cancer

European miners worked in uranium mines to extract uranium ore (radon gas is byproduct of uranium decay)

in the 1950’s and 1960’s which group of people were then used to mine uranium

Navajo people of Arizona and New Mexico when the government needed fuel for nuclear weapons

how much dose is assumed each worker received working in the mines

10 Sv or more

received cancerous skin lesions on the hands because of the lack of protection

early radiologists and dentists

why did skin cancer develop in patients

radiation for facials and hair removal treatments

in the 1940’s and early 1950’s doctors diagnosed thymus enlargement in infants, why did this lead to thyroid cancer 10-20 years later

infants were treated with 1.2 Gyt to 60Gyt of radiation to shrink thymus gland

thyroid is so close to the thymus the thyroid gland received substantial dose

what was the average dose to the thyroid across all of the marshal islands

12 Gyt

in the 1950’s to early 1960’s what lead to an increase (almost double) in the number of breast cancer cases

radiation was used to treat for relief of postpartum mastitis

which population of women have a lower natural incidence of breast cancer

Japanese women

atomic bomb survivors in Japan demonstrated higher incidence of breast cancer, what increase did the relative risk ratio have according to studies

4:1 to 10:1

what did studies show in Japanese survivors about leukemia

that there was a significant increase in leukemia in the exposed compared to the non-exposed

what is this graph indicating

leukemia occurs approx. 2 years after initial exposure and rises to highest level between 7-10 years, then at 30 yrs declines to almost 0

contracting leukemia is directly _______ to magnitude of radiation exposure and follows a ______ dose-response

proportional , linear non threshold

which type of cancer increased dramatically in the first 10 years after Chernobyl

thyroid cancer

in April of 1996, how many cases of thyroid cancer were diagnosed in children

700 cases

how was there an attempt to prevent thyroid cancer in children

potassium iodide administered intended to block uptake of iodine

some things that lab experiments on animals showed with radiation

• life span of exposed animals was shorter, died sooner

• radiation believed to accelerate all causes of death (nonspecific life span shortening)

• accelerated aging process, more susceptible to diseases

what has the study started in 1982, of approx. 146,000 RT’s shown about radiation exposure

techs who began working before 1940 had slightly higher risk of dying from any type of cancer than those who began working before 1950

which population of RT’s have the greatest risk for breast cancer

those who began working before 1940’s

humans can expect reduced life span of 10 days for every ____ received

0.01 Gy

defined as the production of cataracts, formed by an accumulation of dead cells in the lens of the eye

cataractogensis

which type of dose-response does cataractogenesis follow

threshold non linear

what is the threshold for single exposure to the eye for cataract formation

0.5Gy

a gene that is mutated from a gene involved in normal cell growth

may cause growth of cancer cells, can be inherited or caused by being exposed to substances in the environment that cause cancer

oncogene