LET, RBE, & OER

The theory that small doses of radiation are good for you

Hormesis

What is the LET of diagnostic x-rays

3 Kev/μm

If it took 200 mGy of x-rays but only 40 mGy of neutrons to produce the same biological effect, what is the RBE of the neutrons?

5

Radiosensitizer

Agents that enhance the effect of radiation

RBE

As the LET of radiation increases, the ability to produce biologic damage also increases. This effect is called the relative biologic effectiveness Formula: Dose of standard radiation necessary to produce a given effect/Dose of test radiation necessary to produce the same effect

a decrease in cell size caused by loss of subcellular organelles and substances

Atrophy

OER

Describes the radiation response in tissues. Also known as the oxygen effect. Formula: Dose necessary under anoxic conditions to produce a given effect/ Dose necessary under aerobic conditions to produce the same effect

Cells and tissues are less sensitive to the effects of radiation when in the presence of oxygen.

False

Cells are most sensitive to radiation during DNA synthesis.

False

Low LET radiation will cause a high number of ionizations

False

Radiation doses doled out over a shorter period of time are less damaging than the same dose given out over a longer period time.

False

There is no evidence to support the theory of hormesis.

False

dose is delivered at same dose rate but separated into fractions

Fractioned dose

Which of the following is NOT part of the Law of Bergonie & Tribondeau? a) Young, immature cells and tissues are more sensitive to radiation. b) Stem cells are more sensitive to radiation. c) Cells with high mitotic activity are more sensitive to radiation. d) Cells with a low metabolic activity are more sensitive to radiation.

d) Cells with a low metabolic activity are more sensitive to radiation

The higher the LET, the higher the ________ will be. a) OER b) Wt c) hormesis d) Wr

d) Wr

Fractionation and protraction are used for radiation therapy because they allow the patient to _____. a) recover between doses b) have higher total doses c) repair damaged tissues d) all of the above

d) all of the above

Studies of the effects of radiation show that low doses may _____. a) stimulate the immune system b) extend the life span c) stimulate hormonal responses d) all of the above

d) all of the above

Which of the following types of radiation will cause the highest number of ionizations in a short distance? a) gamma rays b) beta particles c) x-rays d) alpha particles

d) alpha particles

A radiation oncology patient is prescribed 45 Gyt of radiation to target breast cancer. The dose will be given five days a week for 8 weeks. This type of dose is known as: a) radioprotective dose. b) consequential dose. c) protracted dose. d) fractionated dose.

d) fractionated dose

Which dose-response relationship can follow a sigmoid curve? a) linear-nonthreshold b) linear-threshold c) nonlinear-nonthreshold d) nonlinear-threshold

d) nonlinear-threshold

Low LET

ionization occur less frequently, decreasing the probability of interaction with the target molecule.

Human cells cannot recover from radiation damage after there is _____. a) cellular repair b) cellular repopulation c) interphase death d) sublethal damage

c) interphase death

Tissue is _____ radiosensitive under high oxygen conditions and _____ radiosensitive under hypoxic conditions. a) less, equally b) less, more c) more, less d) more, equally

c) more, less

Interphase death

cell death that occurs when the cell dies before replicating

The RBE of diagnostic x-rays is equal to _____. a) 20 b)10 c) 5 d)1

d) 1

What is used to account for the relative radiosensitivity of various tissues and organs: 1) tissue weighting factors (Wt) 2) radiation weighting factors (Wr) 3) absorbed dose a) 1 and 2 only b) 1, 2, and 3 c) 2 and 3 only d) 1 only

d) 1 only

The law of _____ states that the radiosensitivity of living tissue is a function of the metabolism and maturation of that tissue. a) Watson and Crick b) Roentgen and Plank c) Hurter and Driffield d) Bergonie and Tribondeau

d) Bergonie and Tribondeau

Of the choices listed below, which cell type is MOST resistant to radiation? a) Intestinal crypt cells b) Thyroid cells c) Germ cells d) Brain cells

d) Brain cells

550 rad of 220 kVp x-rays are necessary to produce death in a hermit crab. Cobalt-60 gamma rays have a lower LET than 220 kVp x-rays, therefore 1150 rad is required for hermit crab lethality. What is the RBE of Co-60 compared to the 220 kVp x-ray? Round to the nearest tenth.

.5

A radiation oncology patient is prescribed 45 Gyt of radiation to target breast cancer. The dose will be given five days a week for 8 weeks. How much dose will she receive each day of treatment? Round to the nearest tenth and include your units.

1.1 Gyt

Under fully oxygenated conditions, 50% of human cells in culture will be killed by 60 rad of x-rays. If cells are made anoxic, the dose required for 50% lethality is 360 rad. What is the OER?

6

Humans are most radiosensitive during _____. a) fetal stages b) infancy c) adulthood d) old age

a) fetal stages

X-rays are high LET radiation.

False

In 4-6 sentences, explain hormesis. How does it work? Is there any evidence that hormesis exists?

Hormesis is the theory or idea that although high doses of radiation can be very harmful or even lethal, small amounts of radiation may actually be beneficial. The idea is that the small amounts of radiation triggers repair in the organism's cells, and even repair other damages not necessarily caused by radiation. There is some evidence that it may be helpful; studies have been conducted on survivors of Hiroshima and Nagasaki; some survivors who received 100mSv had a lower incidence of leukemia than a similar cohort who did not have any radiation exposure.

If the dose is delivered continuously but at a lower dose rate

Protracted dose

The oxygen enhancement ratio (OER) compares: a) hypoxic dose to aerobic dose b) aerobic dose to hypoxic dose c) standard dose to test dose d) test dose to standard dose

a) hypoxic dose is aerobic dose

In 4-6 sentences, explain the oxygen effect. What is relationship between the oxygen effect and low and high LET radiation? How is the oxygen effect used to help cancer patients?

Studies have shown that cells and tissues are much more sensitive to the effects of radiation when in the presence of oxygen. Cells that are hypoxic, or irratidated under low-oxygen conditions are more resistant to radiation. Cells or tissues irradiated under anoxic conditions, or where there is no oxygen, would be the most resistant to radiation. In general, the oxygen effect is more pronounced with low LET radiation. The oxygen effect is basically non-existent with high LET radiation. This is likely because the high LET radiation is so damaging that any additional killing benefit the oxygen might have is overshadowed by the damage already done by the radiation. So as LET increases, damage caused by oxygen will decrease. Cancer patients may benefit from the oxygen effect if pulses of oxygen are delivered within a few microseconds after radiation exposure. This helps to make the cancer cells (and invariably some surrounding healthy cells) more sensitive to the radiation and hopefully cause them to die. If the cancer can be eradicated in this manner, then hopefully with time, the healthy cells will recover by repairing themselves and repopulating with healthy, normal, non-cancerous cells.

Alpha particles cause more double-strand DNA breaks than x-rays.

True

An example of a radioprotecting chemical is cysteine.

True

As OER decreases, RBE will increase until it reaches as LET of about 100keV/µm.

True

LET can help estimate the amount of damage produced by the absorption of a given amount of radiation energy.

True

In 4-6 sentences, compare and contrast direct and indirect mechanisms of DNA damage.

When the radiation physically interacts with the DNA, ionizing an atom in the DNA molecule, or physically breaking a bond in the molecule, whether it's a nucleotide bond that's broken or a phosphate bond or otherwise damaging the molecule, we call it direct damage. The damage to the DNA molecule may or may not be repairable depending on the severity of the damage. In indirect damage, the radiation doesn't interact with the DNA molecule itself, but rather the radiation interacts with other molecules in the cell. Cells are 80% water, so it's most likely that the radiation will interact with a water molecule and break it into two parts, a positively charged hydrogen ion (H+), and a negatively charged hydroxide(OH- ) ion. When this occurs, the free radical hydroxide molecule may go on to interact with the DNA molecule. In order for an indirect action to take place and for the DNA to be damaged by this, the reaction with the water has to take place very close to the DNA molecule.

What is the effect on relative biologic effectiveness (RBE) as linear energy transfer (LET) increases? a) As LET increases, RBE increases b) As LET increases, RBE stabilizes c) LET has no effect on RBE d) As LET increases, RBE decreases

a) As LET increases, RBE increases

Which cells are most sensitive to radiation? a) Cells in an oxygen rich environment (aerobic.) b) Cells in a zero oxygen environment (anaerobic.) c) Cells in a low oxygen environment (hypoxic.) d) Oxygen does not affect a cell's sensitivity to radiation.

a) Cells in an oxygen rich environment (aerobic)

_____ is a measure of the rate that energy is transferred from ionizing radiation to soft tissue. a) LET b) RBE c) MeV d) OER

a) LET

When are cells most sensitive to radiation? a) Mitosis b) Hormesis c) Interphase d) Cytokinesis

a) Mitosis

Linear energy transfer: a) is a measurement of the amount of energy absorbed per unit dose b) is a measurement of the ratio of standard dose to test subject dose c) is a measurement of the tissue weighting factor d) is a measurement of the ratio of hypoxic dose to aerobic dose

a) is a measurement of the amount of energy absorbed per unit dose

A _____ response to radiation is directly proportional to the dose received. a) linear b) nonlinear c) curvilinear d) non-threshold

a) linear

Radiation induced genetic damage follows a _____ dose-response relationship. a) linear-nonthreshold b) linear-threshold c) nonlinear-nonthreshold d) nonlinear-threshold

a) linear-nonthreshold

If a response to radiation is expected, no matter how small the dose, then that dose-response is _____. a) non-threshold b) linear c) non-linear d) threshold

a) non-threshold

A protracted dose of radiation is given _____. a) over a long period of time b) all at one short exposure c) in a series of separate doses d) in two large doses

a) over a long period of time

Linear energy transfer (LET) is: 1) a method of expressing radiation quality 2) a measure of the rate at which radiation energy is transferred to soft tissue 3) Absorption of polyenergetic radiation a) 1, 2 and 3 b) 1 and 2 only c) 1 and 3 only d) 1 only

b) 1 and 2 only

Which of the following may be used as a "standard" for calculating RBE? More than one answer is possible; check all that apply. 1) Co-60 gamma rays 2) 100 MeV Alpha particles 3) 90 keV protons 4) 250 kVp x-rays a) 1 and 2 only b) 1 and 4 only c) 1, 2, 4 only d) 1, 2, 3 and 4

b) 1 and 4 only

As LET increases, what happens to the ability of ionizing radiation to cause biological damage? a) There is no relationship between LET and biological damage. b) Biological damage increases c) Biological damage decreases d) Biological damage does not increase or decrease; it remains constant.

b) Biological damage increases

The idea that although high doses of radiation can be harmful or lethal, small doses have the potential to be beneficial is known as: a) Oxygenation theory b) Hormesis c) Zero thesis d) Fractionation

b) Hormesis

Which of the following are parts of the law of Bergonie and Tribondeau? a) The more mature a cell, the more radiosensitive it is b) Stem cells are radiosensitive c) A fetus is less radiosensitive than an adult d) When metabolism is high, radiosensitivity is low

b) Stem cells are radiosensitive

The human application of radioprotective agents would _____. a) double radiation damage b) be fatally toxic c) reduce radiation effects by half d) reduce radiation effects by one fourth

b) be fatally toxic

The human dose-response relationship at low ranges of radiation is calculated using _____. a) known responses from low doses b) extrapolation from high ranges c) human experiments d) all of the above

b) extrapolation from high ranges

A dose of 10 Gy given to a patient in 5 doses of 2 Gy per day is a _____ dose. a) protracted b) fractionated c) diagnostic d) fatal

b) fractionated

The possible beneficial effect of a small amount of radiation is called _____. a) radiosensitizing b) hormesis c) radioprotection d) protraction

b) hormesis

Tissues that are _____ with a _____ metabolic rate are more radiosensitive. a) immature, low b) immature, high c) mature, low d) mature, high

b) immature, high

LET is measured in which of the following? a) rad/µm b) keV/µm c) keV/rad d) Gray

b) keV/µm

The LET of diagnostic x-rays is _____ keV/um. a) 0.2 b) 0.3 c) 3.0 d) 50

c) 3.0

How are health effects of radiation at low doses determined? a) Human experiments b) All of the above c) Extrapolation from high doses d) Known responses from low doses

c) Extrapolation from high doses

Which of the following does not affect RBE? a) Radiation quality b) Total dose c) None of the above d) Tissue type e) Biological end point

c) None of the above

Which of the following describes quantitatively the ability of radiation to cause damage? a) Protraction b) OER c) RBE d) LET

c) RBE

How are RBE and LET related? a) There is no relationship between LET and RBE b) LET and RBE are equivalent c) RBE and LET are directly related d) LET and RBE are inversely related

c) RBE and LET are directly related

A chemical present when a cell is irradiated that makes the cell more susceptible to DNA damage and cell death is known as a: a) Carcinogen b) Radioprotector c) Radiosensitizer d) OER

c) Radiosensitizer

Agents that enhance the effect of radiation are called: a) Radioprotectors b) Radioshields c) Radiosensitizers d) Radiointensifiers

c) Radiosensitizers

OER is ________ for ______ LET radiation. a) lowest, low b) highest, high c) highest, low d) none of the above

c) highest, low

As LET _____, the RBE _____. a) increases, remains the same b) decreases, remains the same c) increases, increases d) increases, decreases

c) increases, increases

If a response to radiation is expected, no matter how small the dose, then that dose-response is _____. a) linear b) nonlinear c) nonthreshold d) threshold

c) nonthreshold

The effects of radiation to biologic material are dependent on several factors. If a quantity of radiation is delivered to a body over a long period of time, the effect: a) will be greater than if it were delivered all at one time b) has no relation to how it is delivered in time c) will be less than if it were delivered all at one time d) is solely dependent on the radiation quality

c) will be less than if it were delivered all at one time

_____ is a measure of the rate that energy is transferred from ionizing radiation to soft tissue. a) OER b) RBE c) MeV d) LET

d) LET

When a radiation dose is given continuously at a lower rate, over a longer period of time, it is known as: a) Hormesis b) Fractionation c) Pulsed d) Protraction

d) Protraction

The radiation effect that kills cell before its next division is known as: a) sublethal radiation damage b) hormesis c) threshold dose d) interphase death

d) interphase death

High LET

ionizations occur frequently, increasing the probability of interaction with the target molecule

serving to protect or aiding in protecting against the injurious effect of radiations

radioprotectors