Effects of Ionizations on Cells

Study Notes

Overview of Radiation-Induced Ionizations

Ionizations from radiation can directly target cellular molecules or indirectly affect water molecules, generating water-derived radicals.
Radicals quickly react with nearby molecules, leading to bond breakage or oxidation.
The primary consequence of radiation damage in cells is the occurrence of DNA breaks.

DNA Damage Mechanisms

Double-strand breaks in DNA complicate repair processes, often resulting in erroneous rejoining of broken ends.
Misrepair can lead to:
- Mutations within the DNA sequence.
- Chromosome aberrations, affecting genetic stability.
- Potential cell death due to extensive damage.

Characteristics of DNA Damage by Radiation

Deletion of DNA segments is the main form of radiation damage in surviving cells.
This may occur due to:
- Misrepair where two separate double-strand breaks lead to joining of outer DNA ends, causing loss of the central fragment.
- An enzymatic process that digests nucleotides at broken ends, complicating repair efforts.

Biological Effects of Different Radiation Types

Biological effects of radiation exposure vary based on the type and energy of the radiation.
High-linear-energy-transfer (high-LET) radiation, such as neutrons, causes dense ionizations along its path, resulting in significant biological damage.
Low-LET radiation, like X-rays and gamma rays, causes sparser ionizations that are more uniformly distributed throughout the cell.

Radiation Dose and Its Impact

Radiation dose is measured by the energy imparted per unit biological material, typically represented as the number of ionizations per target cell.
High-LET radiation is more destructive due to concentrated energy release in a small cellular region, leading to localized DNA damage that is harder to repair.
Low-LET radiation results in diffuse damage, making it easier for cells to manage and repair the induced ionizations.

Postero-anterior – Ulnar Deviation

Patient sits at the table with the affected side closest.
Arm extended across the table, elbow flexed, and forearm pronated.
Shoulder, elbow, and wrist ideally level with the tabletop.
Wrist positioned over one-quarter of the cassette with adduction (ulnar deviation).
Ensure radial and ulnar styloid processes are equidistant from the cassette.
Hand and lower forearm immobilized using sandbags.

Anterior Oblique – Ulnar Deviation

Hand and wrist rotated 45 degrees externally from the postero-anterior position.
The hand placed over an unexposed quarter of the cassette.
Hand remains adducted in ulnar deviation.
Support provided with a non-opaque pad under the thumb.
Forearm immobilized using a sandbag.

Posterior Oblique

From the anterior oblique position, hand and wrist rotated externally 90 degrees.
The posterior aspect of the hand and wrist positioned at 45 degrees to the cassette.
Wrist placed over an unexposed quarter of the cassette.
Supported on a 45-degree non-opaque foam pad.
Forearm immobilized using a sandbag.

Lateral

Hand and wrist rotated internally 45 degrees from the posterior oblique position.
Medial aspect of the wrist in contact with the cassette.
Hand adjusted to superimpose the radial and ulnar styloid processes.
Hand and wrist immobilized using non-opaque pads and sandbags.

Postero-anterior

Patient seated with the affected side nearest the table.
Elbow flexed at 90 degrees and arm abducted, resting on the cassette.
Shoulder height aligned with the forearm if patient mobility allows.
Wrist placed on half of the cassette to include the lower radius, ulna, and proximal metacarpals.
Fingers flexed slightly to maintain anterior wrist contact with the cassette.
Wrist adjusted for equidistance of radial and ulnar styloid processes from the cassette.
Forearm immobilized using a sandbag.

Oblique (Anterior Oblique)

Patient positioned similarly as in previous setups with the affected side nearest.
Elbow flexed 90 degrees and arm abducted, resting palm down on the tabletop.
Shoulder height aligned with forearm if feasible for mobility.
Wrist adjusted on the cassette to include lower radius, ulna, and proximal metacarpals.
Hand externally rotated 45 degrees and supported with a non-opaque pad.
Forearm immobilized using a sandbag.

Description

This quiz explores how radiation-induced ionizations affect cellular components and the mechanisms that lead to DNA damage. Understand the direct and indirect impacts of radicals generated by ionizations and the implications for DNA integrity. Delve into the challenges of repairing double-strand breaks and the potential consequences for cell function.