Radiation Biology

Front 1

Structural or morphologic response after radiation is usually grouped into two phases

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acute/early or chronic/late

Front 2

Acute or early changes observed within _____ months of treatment

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6 months

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Chronic or late changes occur

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more than 6 months later

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The appearance of late changes is a consequence of early changes that were____ and ______.

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irreversible and progressive

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The probability of late changes occurring depends on the __, __, ___.

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dose administered, the volume irradiated, and the healing ability of the irradiated structure (organ)

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Organ healing can occur after radiation exposure by the process of ___ or ____.

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regeneration or repair

Front 7

Regeneration refers to the replacement of damaged cells by

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replacement of damaged cells by the same cell type.

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Refers to the replacement of damaged cells by a different cell type, thus resulting in scar formation or fibrosis

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repair

Front 9

T/F Healing by repair can restore an organ to its preirradiated state

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False

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Irreversible early changes hear by process of

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repair

Front 11

The type of healing occurs is a function of the ____ received and the ___ of the organ receiving it.

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dose, volume

Front 12

Irradiation of skin and lung tissue with a dose of ___ induces severe early skin changes but minimal early lung changes. However the same tissues 6 to 12 wks later there is minimal late changes in skin, but severe changes in the lung.

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2000 cGy

Front 13

The most common early/acute changes after irradiation include

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inflammation, edema, and hemorrhaging in the exposed area

Front 14

If doses are ___, these early changes may progress to changes may progress to characteristic ____ or _____ changes, that include fibrosis, atrophy, and ulceration.

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high enough, late or chronic

Front 15

The most severe late response is

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tissue necrosis or death

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RTOG

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Radiation Therapy Oncology Group

Front 17

___ syndrome in humans is induced by total body doses of 100 to 1000 cGy

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Hemopoietic

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(hemopoietic) LD 50/60 for humans is estimated between __ and ___ cGy but varies with age, health, and gender.

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350 and 450

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Male or Female more resistant

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Females

Front 20

After ___ to ___ death may occur in 4 to 6 weeks.

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300-500

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No record exists of human survival when the body dose exceeds ___ cGy

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1000 cGy

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____ syndrome if the total body dose is between 1000 and 10,000 cGy

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Gastrointestinal

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Gastrointestinal may be induced as low as ___ cGy and overlaps with ehe cerebrovascular syndrome at doses of ____ cGy or more.

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600 cGy, 5000 cGy

Front 24

The mean survival for GI syndrome

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3 to 10 days or upt to 2 weeks with medical support

Front 25

____ syndrome occurs after doses of 10,000 cGy or more

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Cerebrovascular formerly CNS syndrome

Front 26

LD 100 in this dose range

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1000 cGy

Front 27

In utero radiation damage is manifested as

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lethal effects, congenital abnormalities present at birth, or late effects observed years later.

Front 28

These effects in utero can be produced by

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1. irradiation of the sperm or ovum before fertilization, thus resulting in inherited effects or 2. exposure of the fetus to radiation, thus resulting in congenital defects

Front 29

When is the embryo known as a fetus and enters the fetal growth stage

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sixth week

Front 30

The latent period for an effect is ____ porportional to radiation dose

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inversely

Front 31

The biological response to low doses is not observable for extended periods, ranging for years to generations is termed

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late effects

Front 32

The biological esponse to low doses is not observable for extended periods, ranging for years to generations with body cells involved is termed

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somatic effects

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The biological esponse to low doses is not observable for extended periods, ranging for years to generations with reproductive (germ) cells involved is termed

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genetic effects

Front 34

The time interval between irradiation and the appearance of a malignancy is known as the

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latent period

Front 35

The most important late somatic effect induced by radiation is

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carcinogenesis

Front 36

Carcinogenesis is considered to be an ____ event

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all-or-nothing, meaning any dose no matter how low has some potential of inducing cancer

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Cnacer induction is therefore a non-threshold event with the probability of an effect ____ as dose increases

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increasing

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Carcinogenesis is therefore an example of a ____ effect, in which every dose carries some magnitude of risk

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stochastic

Front 39

The latent period for leukemia induced by radiation is usually ___ to ___ years, with peak incidence approximately ___ to ___ years after exposure.

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4 to 7, 7 to 10

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#1 cancer in the world

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skin carcinoma

Front 41

___ and ___ have been the most frequently observed skin cancers following radiation exposure

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Squamous cell and basal cell carcinomas

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The best example of radiation induced bone cancer

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group of young female watch-dial painters who used radium to paint clock faces for a company

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German pitchblende miners suffered from a "mountain sickness"

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lung cancer

Front 44

The naturally deposits of radioactive material in the rocks of the earth decay through a long series of steps until they reach a stable isotope of lead. One of these steps involve ____ ___

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radon gas

Front 45

Radon gas is ___%

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55%

Front 46

1930's irradiation of enlarged thymuses in children with dose 1200 to 6000 cGy was a popular treatment. ___% ____ cancer was observed.

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100% of thyroid cancer

Front 47

___ ___ ___ can occur in an irradiated individual and exposure of reproductive (germ) cells in that individual may affect future generations.

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Somatic late effects

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_____ permanent, heritable, transmittable to generations, and generally detrimental occur spontaneously in genes and DNA

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Mutations

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The number of spntaneous mutations that occur in each generation of an organism is

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mutation frequency

Front 50

The classic study that demonstrated mutagenic potential of radiation on ___ ___ an observed the mutation frequencies in the next several generations performed by

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fruit flies, H. J. Muller

Front 51

The goal of radiation therapy for cancer is to

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eradicate the tumor while not destroying normal tissues in the treatment field

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actively mitotic cells that are responsible for tumor growth belong to ___ and are viable

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Cells belonging to group 1

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The percentage of group 1 cells in a tumor type usually varies for __% to __% and is termed __ __

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30% to 50%, growth fraction (GF)

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The rate at which tumors grow depends on 3 major factors:

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1. the division rate of proliferating parenchymal cells 2. the percentage of these cells in the tumor (GF) 3. the degree of cell loss form the tumor

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Tumor growth is characteristically ____ compared with that of normal cells

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unorganized

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During their early growth stages tumors begin to outgrow their

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vascular supply

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The differing levels of oxygen availability

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oxygen tension

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The oxygen tension for the tumor cells depended on their____ of the functioning ___ ___.

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proximity, blood vessel

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Thomlinson and Gray concluded that tumor cells located more than ___ um from the nearest blood vessels (capillaries) are ___ and unable to proliferate

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200, anoxic (no oxygen available)

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Tumor cells___ to blood vessels, are well oxygenated or ___. They are actively dividing and compose the GF of the tumor

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closest, oxic

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Between oxic and anoxic cells are cells exposed to gradually

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decreasing oxygen tensions, known as hypoxic cells

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__% of tumor-cell population may be hypoxic

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15%

Front 63

The radioresponse of a tumor depends on these ___ ____

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cell poplulations

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The vasculature network that forms in each growing tumor with factors of ___, ___, and ___ ultimately give rise to oxic, hypoxic, and anoxic cell populations in that tumor

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division rate, GF, and cell loss

Front 65

Modern radiation therapy treatments are given in daily fractions over an extended period ___ or ___ weeks

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6 to 8

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Daily fractions over an extended period of time to a high total dose, while sparing normal tissues known as

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fractionation

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A fractionation dose is ___ efficient biologically than a single dose. Therefore higher total doses a necessary to produce the same damage

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less

Front 68

The biological effects on tissue from fractionated radiation therapy depend on the 4 R's of radiaton biology

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1. repopulation 2. redistribution 3. repair 4. reoxygenation

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Repair of sublethat damage has occurred within ____ of radiation exposure in normal and tumor cells in vitro

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hours

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Repair of sublethal damage is ___ dependant

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oxygen

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Reoxygenation is presumed to apply only to

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tumors

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The process by which hypoxic cells gain access to oxygen and become radiosensitive between radiation fractions

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reoxygenation

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___, ____, ___, ___, and ___ have all been used with varying degrees of success to improve tumor response

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Radiosensitizers radioprotectors, high-LET radiations,chemotherapy agents, and hyperthermia (heat)

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The ____ is related to the treatment schedule in terms of total dose and time with the clinical outcome , including early effects, lated effects, and tumor cure.

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isoeffect curves

Front 75

Tolerance doses have therfore been established for normal tissue in terms of the total dose delivered by a standard fractionation schedule that causes a minimal __% of maximal __% complication rate within 5 years

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TD 5/5 - tissue dose associated with a 5% injury rate within 5 years
TD 50/5- tissue dose associated with a 50% injury rate within 5 years

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IMRT

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intensity modulated radiation therapy

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IMRT does

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reduces radiation toxicity to surrounding tissues, altering the ratio of normal tissue dose to tumor dose

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TD 5/5 Brain

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5000-6000

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TD 5/5 Eye- Lens

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500

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TD 5/5 Fetus

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200

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TD 5/5 Heart

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4500-7000

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TD 5/5 Intestine

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4500-5000

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TD 5/5 Kidney

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1500-2000

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TD 5/5 Liver

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1500-2500

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TD 5/5 Lung

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1500-3000

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TD 5/5 Spinal Cord

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4500