Radiobiology 2 MCQ

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Questions and Answers

What is the primary reason cancer cells are more radiosensitive than normal cells?

They are less affected by antioxidants.

They have more stable organic compounds.

They have unusually high mitotic rates. (correct)

They have less DNA present during mitosis.

Which interaction occurs when radiation interacts with cellular water?

Direct interaction

Hydrolytic interaction

Indirect interaction (correct)

Radical interaction

What compound is formed when two hydroxyl molecules recombine?

Hydrogen peroxide (correct)

Ozone

Water

Hydrogen

What type of cellular injury results in a dose-dependent delay in cell division?

Division delay Signup and view all the answers

At what radiation dose is division delay observed to begin?

0.5 Gy Signup and view all the answers

Which of the following scenarios is NOT associated with cellular injury from ionizing radiation?

Increased mitotic activity Signup and view all the answers

What is the role of antioxidants in relation to indirect radiation interactions?

They prevent recombination into hydrogen peroxide. Signup and view all the answers

Which of the following best describes interphase death?

Immediate cell death through apoptosis. Signup and view all the answers

What can result from the formation of stable organic hydrogen peroxide in cells?

Loss of essential enzymes in the cell Signup and view all the answers

Which cellular mechanism is most commonly associated with apoptosis after radiation exposure?

Lymphocyte response Signup and view all the answers

At what dose level does reproductive failure transition from random to linear and nonrandom?

1.5 Gy Signup and view all the answers

Which type of radiation requires a higher absorbed dose to produce the same biological effect as X-rays?

Neutrons Signup and view all the answers

What type of cell typically experiences interphase death at lower doses due to rapid division?

Undifferentiated cells Signup and view all the answers

What is the unit of measure for the absorbed dose?

Grays Signup and view all the answers

What is the main factor that affects the energy loss effects of radiation?

Radiation type Signup and view all the answers

What mechanism might cause cell death many generations after initial radiation exposure?

Aging process Signup and view all the answers

How does cell reproduction influence the likelihood of interphase death after radiation exposure?

Higher reproduction increases interphase death Signup and view all the answers

Which particles are set in motion when X-rays are absorbed?

Electrons Signup and view all the answers

What effect does the density of ionization have on radiation's interaction with DNA?

Increases the probability of direct interaction Signup and view all the answers

In comparing different types of radiation, which one is typically used as the standard?

X-ray radiation Signup and view all the answers

What phenomenon occurs when high LET radiation kills more cells than actually available?

Overkill effect Signup and view all the answers

How does RBE change as LET increases beyond a certain point?

RBE initially increases and then decreases Signup and view all the answers

Which type of radiation is associated with a low RBE due to low probability of causing double-strand breaks?

Sparsely ionizing X-rays Signup and view all the answers

What does the linear–no threshold dose-response model propose about radiation exposure?

Any amount of radiation exposure can be harmful Signup and view all the answers

Which dosage-response model is characterized by the idea that low-dose radiation exposure could be beneficial?

Radiation hormesis Signup and view all the answers

In the context of RBE, what does sparsely ionizing radiation imply?

It produces fewer ionizations per unit distance. Signup and view all the answers

Which dose-response model is most likely to be used to extrapolate high-dose effects to low-dose ranges?

Linear quadratic Signup and view all the answers

What is a key impact of densely ionizing radiation on RBE when calculated?

Decreases RBE because of overkill effect Signup and view all the answers

What key concept explains the inefficiency of high LET radiation in producing RBE?

Overkill effect Signup and view all the answers

What can be considered a limitation when using the linear–threshold model in radiation biology?

Neglects beneficial effects at low doses Signup and view all the answers

Which factor does not influence the Linear Energy Transfer (LET) of radiation?

Type of biological effect Signup and view all the answers

What is the optimal LET value for producing significant biological effects?

100 keV/μm Signup and view all the answers

Which type of radiation generally has the highest relative biological effectiveness (RBE)?

Alpha particles Signup and view all the answers

What does the acronym RBE stand for in radiation biology?

Relative Biological Effectiveness Signup and view all the answers

How is Linear Energy Transfer (LET) expressed mathematically?

dE/dx Signup and view all the answers

What type of energy deposition is associated with low LET radiation?

Low energy sparsely distributed Signup and view all the answers

What are double strand breaks (DSBs) in biological contexts often caused by?

High LET radiation Signup and view all the answers

Which of the following best describes the energy loss effect of alpha particles compared to gamma rays?

Alpha particles impart energy in a short distance while gamma rays are more penetrating. Signup and view all the answers

What is a significant characteristic of high LET radiation in terms of biological effects?

It causes a greater likelihood of DSBs. Signup and view all the answers

How is the dose from different radiation types normalized in terms of RBE?

By the ratio of doses from 250 keV X-rays to another radiation source Signup and view all the answers

Study Notes

Cell Cycle Phases

The cell cycle is a series of events that lead to cell growth and division
The cell cycle has several phases: G0, G1, S, G2, and mitosis.
G0: Cell cycle arrest; the cell is not actively dividing.
G1: Cellular contents, excluding the chromosomes, are duplicated.
S: Each of the 46 chromosomes is duplicated by the cell.
G2: The cell "double checks" the duplicated chromosomes for error, making any needed repairs.
Mitosis: Cell division
Cytokinesis: The splitting of the cell.

Cell Cycle Times

CHO hamster cells have a cell cycle time ranging from 11 hours to 24 hours.
HeLa human cells have a cell cycle time ranging from approximately 24 hours to 48 to 72 hours.

Radiosensitivity

More DNA is present in one area at the S phase.
Increased chromatin in cancer cells makes them more radiosensitive than normal cells.
The S phase is considered the most radiosensitive time in the cell cycle, as more DNA is present in one area at that point in the cycle. Increased chromatin in cancer cells, as a result of unusually high mitotic rates, also leads to increased radiosensitivity.

Indirect Interaction

Radiation interacts with water molecules rather than the macromolecules in the cell.
This water interaction results in the hydrolysis of water.
The products of this interaction are hydrogen atoms and hydroxyl radicals.
Hydroxyl molecules recombine to form hydrogen peroxide, which in the cell readily combines with other organic compounds to form stable organic hydrogen peroxide molecules.
This process may result in the loss of essential enzymes, leading to cell death or future mutations.

Antioxidants

Antioxidants block the recombination of hydroxyl radicals, preventing stable organic hydrogen peroxide compounds from forming.
This process by which the body can defend itself from indirect radiation interactions is why antioxidants have received so much attention lately as a potential cancer prevention agent.

Hydrolysis of Water

Ionizing radiation interacting with water results in the formation of hydrogen ions and hydroxyl radicals.
Antioxidants can recombine to create water, or a stable compound, but without them, unstable hydrogen peroxide molecules can be formed from hydroxyl free radicals.
If these molecules combine with an organic molecule, permanent damage can occur.
The resulting damage leads to the lack of essential enzymes or eventual cell death.

Cellular Injury

Ionizing radiation exposure can cause three types of cellular injury: division delay, reproductive failure, and interphase death.
Division delay involves a temporary delay in cell division, with the delay dependent on the dose.
Reproductive failure appears when cells stop successful mitosis completion.
Interphase cell death is a fast, relatively prompt cell death event initiated by apoptosis.
Some cancer cells also show apoptosis in response to radiation.

RBE (Relative Biological Effectiveness)

A measure of the effectiveness of different radiation types in producing a biological effect.
Lower LET radiation (like gamma rays, X-rays) have a lower RBE because they deposit energy more sparsely in the cell.
Higher LET radiation (like alpha particles) have a higher RBE because they deposit energy more densely in the cell.
To adjust for differences in radiation quality, radiation dose is often adjusted using equivalent doses.
Equal doses of different radiation types do not produce equal biologic effects.
For low LET radiation RBE is approximately equivalent to LET

Linear Energy Transfer (LET)

The rate at which energy is deposited as a charged particle travels through matter.
LET depends on differing qualities of radiation type.
LET is determined by quality of radiation, its quantity, the dose of radiation, and the exposure conditions. For example alpha, neutrons, protons, and electrons have significantly different LETs, thereby indicating different energy transfer capabilities. The units for LET are typically keV/µm (kilo electron volts per micrometer).
The type of particle and energy determine the amount of energy deposited per unit path length.
This is related to the probability of producing a double strand break, and to biological effects.

Dose-Response Models

There are different theoretical dose-response models to explain radiation effects.
These range from a linear-no-threshold model (where any dose of radiation is harmful), to a linear-threshold model (where some threshold dose is needed before cell injury occurs); or to a linear quadratic model (that introduces a quadratic component to cell damage).
These models are used to extrapolate the effects from high-dose radiation to low-dose radiation exposure to estimate outcomes and to quantify the probability of harmful effects.

Optimal LET

The optimal or most effective LET for causing biological effects is about 100 keV/µm.
At this density, ionizing events occur roughly equal to the DNA double helix diameter.
This causes damage in the form of double-strand DNA breaks, which is the basis of many biological effects.
An X-ray's lower LET would have a lower RBE, resulting in less cell damage with equal dose as a higher LET particle.

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Description

Explore the different phases of the cell cycle, including G0, G1, S, G2, and mitosis, as well as the time it takes for CHO and HeLa cells to complete their cycles. Understand the concept of radiosensitivity during these phases, particularly focusing on the S phase. This quiz will deepen your knowledge about cellular processes and their implications in cancer cells.