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Radiation Biology. Cellular Level Cell Sensitivity Radiolysis of Water Direct Effect/Indirect Effect Target Theory Radiation Effect Early Effects Prodromal/Latent period/Manifest Illness Hematopoietic Syndrome GI Syndrome CNS Syndrome Local tissue damage Late Effects

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radiation biology

Radiation Biology

Cellular Level

Cell Sensitivity

Radiolysis of Water

Direct Effect/Indirect Effect

Target Theory

Radiation Effect

Early Effects

Prodromal/Latent period/Manifest Illness

Hematopoietic Syndrome

GI Syndrome

CNS Syndrome

Local tissue damage

Late Effects

Local Tissue Effect

Life Span shortening

Radiation Protection

Time Distance Shielding

Shield Types



Cell Sensitivity

  • Early Effect:
  • radiation response occurs within minutes/days after exposure
  • acute radiation syndrome
  • local tissue damage
  • Late Effect:
  • radiation response not observable for months or years
  • leukemia
      • cataracts
  • other cancers
  • local tissue damage
  • Life span shortening
  • genetic damage

Linear Response to radiation:

  • Non-threshold
    • Assumes no dose is safe
  • Threshold assumes
    • Minimum dose needed to produce a response



A dose response relationship is produced by extrapolating high dose experimental

data to low doses.

cell sensitivity2

Diagnostic radiology is almost exclusively concerned with the late of effects for radiation exposure. This assumes a linear non-threshold dose-response relationship. However, no dose is considered safe.

Cell Sensitivity
basic cell structure
Basic Cell Structure
  • Two parts:
    • Nucleus- contains DNA
    • Cytoplasm is 80% water
  • DNA is at risk when a cell is exposed to ionizing radiation

Radiolysis of Water

Ionization radiation interacts with a water (H2O). Water dissociates into

2 ions. This process creates free radicals. These are uncharged molecules

containing as single unpaired electron in outer shell.

radiolysis of water

H 2 O molecules -

  • Ejection of electron = free radical
  • H2 0 2 = hydrogen peroxide
Radiolysis of Water

Target Theory

Target theory suggests that a key molecule must be

inactivated. The key molecule is assumed to be DNA.

  • When interaction occurs between radiation and target molecule, it is
  • considered a “hit”
  • An indirect hit has a larger target area because of the mobility
  • of the free radicals
  • Radiation acts randomly.
acute radiation syndrome

Three different levels of exposure effects:

  • Hematologic syndrome
  • GI syndrome
  • CNS syndrome

Acute Radiation Syndrome – full body exposure given in a few minutes.

early effects

Each syndrome has 3 main sub-stages

prodromal stage

latent stage

manifest illness

cell death/repair

Early Effects
total body response to radiation

Acute Radiation Syndromes – full body exposure given in a few minutes.

  • 3 stages of response:

1. Prodromal -NVD stage (nausea, vomiting, diarrhea)

2. Latent Period-Feels well while undergoing biological changes

3. Manifest Illness-Full effects felt, leads to recovery or death

Total Body Response to Radiation
3 radiation syndromes

Hematologic : results in infection, hemorrhage & anemia

  • Gastrointestinal : results in diarrhea, nausea & vomiting, fever
  • Central Nervous System : results in convulsions, coma, & eventual death from increased intracranial pressure.

CNS least sensitive in ADULTS –

MOST sensitive in the FETUS

3 Radiation Syndromes
exposure in soil water

For Chernobyl:

  • 11,000 mrem- current background in red zones
  • 12 mrem is your average background radiation.
  • This is a thousand times greater than the normal background level of radiation
  • Approximately 15-20% of babies are born healthy.
Exposure in soil & water
late effects

Late Effects

    • Local Tissue Effect
      • Erythema
      • Cataracts
    • Life Span Shortening
    • Cancers/Malignancies
    • Genetic Effects
Late Effects
late effects of radiation

Somatic Effects: develop in the individual who is exposed

    • Most common:
      • Skin Damage, Cataract formation & Carcinogenesis
  • Genetic Effects: develop in future generations as a result of damage to germ cells.
Late Effects of Radiation
fukushima japan

Fukushima 50 occupational exposure due to rescue work

After reading this article, write your thoughts on the rescue workers in Japan.

Include allowable exposures to workers, possible acute affects, their prognosis

for long term health.

Fukushima, Japan
cardinal principles of protection

Triad of Radiation Safety

1. Time

2. Distance

3. Shielding

*Apply to the patient & Technologist

Cardinal Principles of Protection
over radiation to skin too much time under beam


Skin burns from 30 min of beam on time

Over Radiation to SkinToo much time under beam

Acute Localized Radiation Effects

The Table 2-2 provides examples of possible radiation effects to skin caused by typical fluoroscopy exposures. Note that patient and technique factors can substantially increase exposure rates, significantly reducing the time necessary for the subsequent effect.

Table 2-2: Dose and Time to Initiate Localized Radiation Effects

.7 of an hour is approximately 42 miutes


This is an actual arm tatoo. Now that’s dedication !

Inverse square law

Inverse square law

Inverse square law


A lead protective shield is placed

  • Between the x-ray tube and the individuals exposed
  • Absorbs unnecessary radiation


  • Lead apron
  • Gloves
  • Thyroid shield
  • Glasses

2. PATIENT – . 5 mm LEAD

  • Gondal Shielding


As Low As Reasonably Achievable