Radiation Biology - Cellular Damage and Effect

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Questions and Answers

Explain the Law of Bergonie and Tribondeau.

The Law of Bergonie and Tribondeau states that cells with high mitotic rate, higher nuclear-cytoplasmic ratio, and high metabolic activity are more sensitive to radiation.

What is the process of Radiolysis of water?

Radiolysis of water is the breakdown of water molecules into hydrogen and hydroxyl radicals when exposed to ionizing radiation.

Define Point Lesions in the context of radiation biology.

Point Lesions are single breaks in the DNA caused by the direct action of ionizing radiation.

What are Indirect Effects of ionizing radiation?

Indirect Effects refer to damage caused by free radicals produced by ionizing radiation rather than direct interaction with the DNA molecule. Signup and view all the answers

Explain Cross-Linking in the context of radiation biology.

Cross-Linking refers to the process where ionizing radiation causes bonds to form between different parts of a DNA molecule or between DNA and other cellular molecules. Signup and view all the answers

Describe the biological significance of Linear Energy Transfer (LET) in radiation therapy.

LET is a measure of how effectively radiation transfers energy to tissue, impacting the biological damage caused by radiation. Signup and view all the answers

What is the main target for the biologic effect of radiation?

DNA Signup and view all the answers

What is the result of cross-linking in DNA molecules?

Increases the viscosity of the macromolecular solution Signup and view all the answers

What is the process by which water molecules surrounding DNA are ionized by radiation, leading to the formation of ions and free radicals?

Radiolysis of water Signup and view all the answers

What type of damage to DNA molecules results in a change or loss of a base, leading to minor modifications of the molecule and abnormalities in the cell?

Point lesions Signup and view all the answers

What percentage of a cell is composed of water, making indirect effects the most common type of radiation damage?

Approximately 80% Signup and view all the answers

What is the term for the reduction of a long, single molecule into smaller molecules, resulting in a decrease in the viscosity of the solution?

Main-chain scission Signup and view all the answers

What are the prerequisites for a suitable lightweight immobilization device?

Fully supported in a comfortable and relaxed position, conforms to patients' contour, sturdy and maintains its shape over time Signup and view all the answers

What is a common material used for head immobilization?

Thermoplastic mesh Signup and view all the answers

Describe the working principle of the Alpha cradle for thorax and breast immobilization.

Mixed foaming agent sealed inside a polyvinyl bag, patient conforms to body contour when positioned in treatment Signup and view all the answers

Explain the purpose of the Vac-lock bag filled with Styrofoam beads.

Retains the shape and contours of the patient when air is removed from the bag Signup and view all the answers

Why are imaging artifacts undesirable in immobilization devices?

Imaging artifacts can interfere with accurate treatment planning and delivery Signup and view all the answers

How do shoulder straps contribute to head and neck immobilization?

They pull the shoulders out of the treatment field for the neck Signup and view all the answers

Study Notes

Immobilization Systems

Pelvic immobilization systems, such as hip-fix systems, vacImmobilization locks, and belly boards, are used during treatments of the pelvic region.
Belly boards are used when the patient is treated prone, allowing the small bowel to drop below the lateral field to avoid severe side effects of irradiation.

Radiation Oncology

Physical Basis of Radiation

Ionizing radiation is used in radiation therapy.
External beam photons or electrons bundles of energy are the most common form of irradiation.
X-rays are produced by machines, such as X-ray machines and linear accelerators (LINAC).
𝛾-rays are emitted from radioactive isotopes, such as Cobalt-60, Cesium-137, and Iridium-192.

Biological Effects of Radiation

The biologic effectiveness of ionizing radiation in living tissue depends on the amount of energy deposited within the tissue and the condition of the biologic system.
Linear Energy Transfer (LET) measures the rate at which energy is transferred from ionizing radiation to soft tissue, expressed in electron volts per micron of tissue (keV/um).
Relative Biologic Effectiveness (RBE) is the ratio of the dose of standard radiation necessary to produce a given effect to the dose of test radiation needed for the same effect.

Cellular Damage and Death

Cellular kill occurs when critical targets within the cell are damaged by radiation and the cell is unable to repair that damage.
DNA is the main target for the biologic effect of radiation.

Types of DNA Damage

Main-chain scission: the breakage of the thread or backbone of the long chain macromolecules, reducing the size of the macromolecules and decreasing the viscosity of the solution.
Cross-linking: produces small spur-like molecules extending off the main chain, increasing the viscosity of the macromolecular solution.
Point lesions: molecular lesions of DNA, resulting in a change or loss of a base, causing minor modification of the molecule, malfunction within the cell, and abnormal gene expression.

Indirect Effects of Radiation

Ionizing of water creates hydroxyl radicals, hydrogen peroxide, hydrated electrons, and other oxygen free radicals capable of interacting with DNA and causing damage.

Immobilization Devices

Immobilizing devices should be strong, durable, and not cause imaging artifacts or affect the treatment beam.
Prerequisites for immobilization include fully supporting the patient in a comfortable and relaxed position, conforming to the patient's contour, and being sturdy and maintaining its shape over time.

Head & Neck Immobilization

Current methods include a variety of masks, molds, and frame systems, with shoulder straps used to pull the shoulders out of the treatment field for the neck.

Thermoplastic Mesh

A polymer that becomes soft and flexible when heated in a water bath, providing a customizable material for reproducible immobilization, commonly used for immobilizing the head but may be used at other sites such as the abdomen or extremities.

Thorax & Breast Immobilization

Cradle-type devices, such as alpha cradle, are used to provide a reproducible positioning system, with a mixed foaming agent sealed inside a polyvinyl bag that conforms to the patient's body contour.

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Description

Test your knowledge on cellular damage and effects of radiation in radiation biology. Learn about the different types of damage that can occur in DNA, including main-chain scission, cross-linking, and point lesions. Understand how cellular kill occurs when critical targets within the cell are damaged by radiation.