Radiation Attenuation and Biological Effects in Radiology

Lecture Purpose: To provide an overview of concepts related to radiation, specifically focusing on attenuation, interactions in radiography, dose measurements, and biological effects of radiation.

Definition: Attenuation refers to the process wherein radiation travels through the body and experiences a change in energy and direction.
- Radiation can lose energy and possibly change direction depending on how it interacts with body tissues.

Key Concept: The interaction responsible for radiographic contrast in imaging.
Important Interaction: Photoelectric effect.
Key Point: KVP (kilovolt peak) is an exposure factor that affects the contrast but is not itself an interaction. KVP alters the quality of the X-rays but does not describe how the interaction occurs.
- Example: KVP is directly linked to the photoelectric effect, which is crucial for creating contrasts in radiographic images.

Five main interactions of X-rays with matter are discussed, with emphasis on which interactions affect radiographer dose and patient imaging.
- Photoelectric Effect: Responsible for contrast because it involves total energy absorption of X-rays, leading to brighter areas on images.
- Compton Scattering: The interaction responsible for higher radiation doses to radiographers, as it involves scattering that does not result in the total absorption of X-rays.

Important Units: SI units for measuring radiation doses include Gray (Gy) and milligray (mGy).
Definitions:
- Gray: SI unit of radiation dose; equivalent to 1 joule of energy absorbed per kilogram of matter.
- Milligray: A smaller unit; 1 Gy = 1,000 mGy.
Radioactivity Units:
- Becquerel (Bq): Represents one disintegration per second.
- Curie (Ci): Traditional unit of radioactivity.

Measurement of Ionization: Defined as the production of positive and negative particles when radiation ionizes atoms in the air.
Unit of Exposure in Air: Measured in coulombs per kilogram.

Definition: The measure of the energy deposited by radiation per unit length of tissue.
Significance: Higher LET values indicate greater biological effects due to increased energy deposition in living tissues as radiation travels through them.

Definition: A graph that indicates the relationship between the dose of radiation and the biological response.
- X-axis represents the dose, while the Y-axis reflects the biological response.
- Shapes can vary: linear, curvilinear, sigmoid, or quadratic.
Threshold vs. Non-threshold:
- Threshold Effects: Require a certain dose to produce effects (e.g., cataracts).
- Non-threshold Effects: Any amount of radiation can contribute to the probability of effects (e.g., cancer).

Stochastic Effects: The probability of occurrence increases with dose, where severity of the effect is independent of the dose.
- Example: Cancer risk associated with radiation.
Non-stochastic Effects: The severity of the effect increases with the dose, ensuring a threshold exists.
- Example: Radiation-induced cataracts.

Somatic Effects: Effects observed in the irradiated individual (e.g., skin burns).
Genetic Effects: Effects that can manifest in future generations, such as mutations.
Understanding Threshold: Some effects (like cataracts) have a threshold, meaning they require a certain dose before they appear.

Radiolysis: The chemical breakdown of water resulting from radiation, leading to the production of free radicals which may damage cellular components.
Oxygen Enhancement Ratio (OER): Cells in the presence of oxygen are more susceptible to radiation damage due to increased sensitivity.

The information discussed covers key concepts in radiation science and its implications for medical imaging and radiological safety, crucial for examinations and practical applications in the field.