Effects of Ionizations on Cells

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.