Radiation Biology: Principles and Laws

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Questions and Answers

Which type of cells are classified as most radiosensitive?

Erythroblasts (correct)

Endothelial cells

Parenchymal cells

Some nerve cells

What characteristic best describes the radiosensitivity of fibroblasts?

Most radioresistant

Intermediate in radiosensitivity (correct)

Most radiosensitive

Relatively radiosensitive

Which organ has the same radiation weighting factor in both Sherer’s textbook and the new ICRP recommendations?

Skin

Liver

Bladder

Red bone marrow (correct)

What property of ionizing radiation is assessed by Linear Energy Transfer (LET)?

Potential tissue damage from exposure Signup and view all the answers

Which of the following best describes cells that do not normally divide but have the capability to do so?

Bone and muscle cells Signup and view all the answers

What is the common feature of biological changes resulting from radiation-induced damage?

They have a defined latent period before being observable. Signup and view all the answers

What effect does ionizing radiation have at the atomic and molecular level?

It initiates chemical changes and energy deposition. Signup and view all the answers

Which of these tissues is categorized as the most radioresistant?

Spermatozoa Signup and view all the answers

What does LET stand for regarding radiation?

Linear Energy Transfer Signup and view all the answers

Which of the following is characterized as low LET radiation?

X-rays Signup and view all the answers

As the LET increases, what happens to the likelihood of biological damage?

It increases. Signup and view all the answers

In diagnostic imaging, what is the typical LET value for X-rays?

3 keV/µm Signup and view all the answers

Which type of radiation is likely to cause more sublethal damage to DNA?

Alpha particles Signup and view all the answers

What is one way that low LET radiation can cause damage to DNA?

Inducing free radicals Signup and view all the answers

Which of the following particles travels further with fewer interactions?

Gamma rays Signup and view all the answers

Which radiation type is NOT considered as high LET?

X-rays Signup and view all the answers

What does RBE stand for in radiation biology?

Relative Biologic Effectiveness Signup and view all the answers

How does the oxygen enhancement ratio (OER) change with increasing LET radiation?

OER decreases with increasing LET. Signup and view all the answers

Which of the following statements about high-LET radiations is true?

They deposit more energy per unit of biological tissue traversed. Signup and view all the answers

What is the RBE of diagnostic x-rays?

1 Signup and view all the answers

Why is biologic tissue more sensitive to radiation in an oxygenated environment?

Oxygen enhances the formation of free radicals. Signup and view all the answers

What is the significance of the Radiation Weighting Factor (WR)?

It is used to calculate the equivalent dose (EqD). Signup and view all the answers

What phenomenon occurs when free radicals combine with oxygen in biological tissues?

Oxygen fixation hypothesis Signup and view all the answers

Which type of radiation is likely to have an RBE greater than 1?

High-LET radiation Signup and view all the answers

What is defined as the total dose of radiation administered in such a short period of time that biological recovery is impossible?

Acute dose Signup and view all the answers

What typically results from irradiation in the dose range of 1-10 Gy?

Reproductive death Signup and view all the answers

Which of the following describes apoptosis?

Programmed cell death before mitosis Signup and view all the answers

What dose is associated with instant death due to irradiation?

1000 Gy Signup and view all the answers

What happens during mitotic death caused by ionizing radiation?

Cells die post-division Signup and view all the answers

Which effect of irradiation occurs when a dose of 0.01 Gy causes failure to start dividing on time?

Mitotic delay Signup and view all the answers

Damage to the cell's nucleus can lead to which of the following?

Chromosome breakage Signup and view all the answers

In what scenario is a cell considered 'dead' even though it may still metabolize?

Reproductive death Signup and view all the answers

What phase of cell division may be used to view radiation-induced chromosome breaks microscopically?

Metaphase Signup and view all the answers

Which of the following is NOT a possible outcome of chromosome breakage?

Form a stable chromatin structure Signup and view all the answers

When do chromosome aberrations occur that lead to chromatid aberrations?

After DNA synthesis Signup and view all the answers

What type of aberration occurs when damage is replicated in DNA synthesis?

Chromosome aberration Signup and view all the answers

Which of the following is an example of a chromosome aberration that can occur in the G1 phase?

Ring formation Signup and view all the answers

What is required for the visual representation of structural radiation damage to chromosomes?

Photomicrograph Signup and view all the answers

At what radiation dose is multi-hit aberrations more likely to happen?

Above 1 Gyt Signup and view all the answers

What type of chromosome aberration represents severe damage to a cell?

Reciprocal translocation Signup and view all the answers

Which type of tissue is characterized by continuous regeneration through mitosis?

Epithelial Tissue Signup and view all the answers

What happens to nerve cells in adults if the nucleus is destroyed?

They die and cannot be restored. Signup and view all the answers

At what point during gestation are developing nerve cells particularly radiosensitive?

8 to 15 weeks Signup and view all the answers

Which dose of radiation may cause temporary sterility in males?

2 Gy Signup and view all the answers

How does radiosensitivity of ova change with age?

It varies and is higher in immature ova. Signup and view all the answers

What is the risk percentage of mental retardation associated with a dose of 0.1-Sv to a fetus?

4% Signup and view all the answers

Which of the following statements about spermatogonia is true?

Immature spermatogonia are radiosensitive and rapidly dividing. Signup and view all the answers

What dose is likely to cause genetic mutations in future offspring?

0.1 Gyt Signup and view all the answers

Study Notes

Fundamental Principles of Radiation Biology

X-ray energy is absorbed by tissue, causing cellular damage.
Two main types of ionizing interactions in diagnostic imaging are photoelectric effect and Compton scatter.
Both interactions remove electrons from atoms, leading to ionization and biological damage.

Law of Bergonie and Tribondeau

Radiosensitivity depends on the cell's metabolic state and reproductive activity.
Mature, fully differentiated cells are less radiosensitive than immature, actively dividing cells.
Younger tissues and organs, with high metabolic activity and high proliferation rates, are more radiosensitive than older, more stable tissues.

Cellular Radiosensitivity Classification

This classification is not required to memorize, focusing instead on Law of Bergonie and Tribondeau.
Rapidly dividing, undifferentiated cells are most radiosensitive. Examples include erythrocytes, spermatogonia, crypt cells of intestines, basal cells of epidermis, intermediate spermatogonia, myelocytes.
Actively dividing, somewhat differentiated cells are relatively radiosensitive (e.g. endothelial cells, fibroblasts).
Irregularly dividing, differentiated cells are relatively radioresistant (e.g. parenchymal cells of the liver and adrenal glands, lymphocytes, bone and muscle cells).
Non-dividing, differentiated cells are most radioresistant (e.g. some nerve cells, erythrocytes, spermatozoa).

Tissue Weighting Factors

Used to calculate the Radiation Weighting Factor (WR) for various organs/tissues.
Values vary between organs, reflecting their radiosensitivity.

Interaction of Radiation with Tissues

Energy deposition occurs very quickly (less than 10^-10 seconds) via excitation, ionization, and thermal heating.
Cellular damage starts with chemical changes at the atomic and molecular levels.
Damage from radiation impact takes time to appear.
Most radiation energy is deposited as heat, while only a fraction causes chemical damage.

Linear Energy Transfer (LET)

A measure of radiation quality, used for radiation weighting factors.
How much energy is transferred per unit length of track traversed.
X-rays and gamma rays have Low LET, traveling further with few interactions, while alpha particles have High LET, traveling shorter distances but with many interactions.
Higher LET radiations are more damaging per unit distance.

Relative Biological Effectiveness (RBE)

Comparing radiation types with different LETs related to a specific biological effect.
Higher LET radiations often have higher RBE values, causing more damage than low LET at an equivalent dose.
RBE varies with radiation type, total dose, and dose rate.

Oxygen Enhancement Ratio (OER)

The ratio of radiation doses in an oxygen-deficient (hypoxic) environment to an oxygen-rich (aerobic) one to achieve the same biological response.
Tissues are more sensitive to radiation when present in an oxygenated environment.
High OER values indicate a strong oxygen dependence, while lower values indicate less effect.

Radiolysis of Water

Water is a major component of the human body.
Ionizing radiation interactions with water can produce highly reactive free radicals (H⁺ , OH^-, H^•, OH^•).
These radicals can damage biological molecules, such as DNA, leading to cellular damage.
The indirect effect of radiation occurs primarily through free radicals produced by water.

Effects of Radiation on DNA and Chromosomes

DNA is considered the primary target molecule.
Direct action involves the radiation interacting directly with the DNA molecule.
Indirect action involves the radiation interacting with water to produce free radicals which then damage the DNA.
Ionizing radiation can cause single-strand and double-strand breaks in DNA which can result in mutations.

Cytogenetic Effects

Radiation-induced damage to chromosomes can lead to various abnormalities, like structural changes (deletions, breaks) and numerical changes (aneuploidy).
The damage can occur in cells during different stages of the cell cycle with varying potential for repair or consequences.
Chromosome damage is possible in all cells; most significant in reproductive cells, affecting future generations directly.

Cell Types and Radiosensitivity

Different cell types exhibit variations in their radiosensitivity, largely dependent on cell division rate, differentiation state, and oxygen content.
Undifferentiated cells, dividing rapidly, are more radiosensitive.
Highly differentiated cells, dividing slowly, are less radiosensitive.
Tissues with high metabolic activity and high proliferation rate tend to be more sensitive.

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Description

This quiz covers fundamental principles of radiation biology, focusing on X-ray energy absorption and its effects on tissue. It also explores the Law of Bergonie and Tribondeau, detailing how radiosensitivity varies among different cell types based on metabolic activity and cell division. Understand the classification of cellular radiosensitivity and its implications in diagnostics.