1. Biological effects of radiation
RAFEEQ

2. Ionizing radiation absorbed by human tissue has
enough energy to remove electrons from the
atoms that make up molecules of the tissue.
When the electron that was shared by the two
atoms to form a molecular bond is dislodged by
ionizing radiation, the bond is broken and thus,
the molecule falls apart. This is a basic model for
understanding radiation damage.

4. Radiation Causes Ionizations of:
cells
which may affect
MOLECULEs
which may affect
TISSUES
which may affect
ORGANS
which may affect
THE WHOLE BODY

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 DNA is the most important material making up the
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chromosome and serve as the master blue print of
the cell.
DNA takes the form of twisted ladder
Sides of ladder are alternating sugar and phosphate
groups
Branching off from each sugar group is four nitrogen
bases,cytosine ,thymine ,adenine and guanine.
Information carried by DNA is detrmined by the
order of the base.

9. Relative Sensitivity of
Cell and Tissue Types
 Lymphocytes
 Hematopoietic (Blood Forming)
 Reproductive cells
 Intestinal Epithelium
 Skin
 Nerve Cells
 Muscle Tissue
 Bone
 Collagen

10. Cells tend to be radiosensitive if they have three
properties:
» Cells that have high division rate
(the time between divisions)
» Cells that have long dividing future
(immature cells in early cellular life)
» Cells that are unspecialized
(cells which have a widely diverse future)

11. Because the human bodyis contains 80%
water molecules, radiation interaction
with water is the principal radiation
interaction in the body.
The ultimate damage occurs to the
target molecule, DNA, which controls
cellular metabolism and reproduction.

12. INTER ACTION WITH ATOM
 When radiation interact with target atoms energy is
deposited resulting ionisation or excitation
 There are two interactions
1. DIRECT ACTION
2.INDIRECT ACTION
Direct action :in this radiation directly interact with DNA and cause
DNA damage.
Indirect action:radiation interacts with water molecules causing
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radiolysis and hence the formation of free radicals,which
is toxic to the tissues

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Indirect Action in Detail
H2O -> H2O+ + eH2O+ is an ion (electrically charged)
H2O+ is also a free radical
 unpaired electron in outer shell
 very reactive
 H2O + H2O +-> H3O+ + OH·
 OH· (hydroxyl radical) is very reactive
 OH * + OH * -------------------- H2O2


16. Radiation Induced Decomposition of
Water Within a Cell
Most abundant molecule within humans: Water
H 2O
+
H2
Incoming
Radiation
H
H 2O
+
OH
eWATER
-
Ho
HO2
H2O2
OH
o
Production of free radicals within the cell can result in indirect effects

18. DNA damage
 Radiation and ions from irradiation can alter the order of
the base ,therefore causing the mutation or cell death.
 When DNA is broken hydrogen bonds between the bases
are broken and they may rejoin in different orders.
 In human cells, we can have as many as a million individual
instances of damage to DNA per cell per day.
 It is remarkable that DNA contains codes that check
whether the DNA is damaged or can repair itself.
 It is like an auto check and repair mechanism. This repair
ability of DNA is vital for maintaining the integrity of the
genetic code and for the normal functioning of the entire
organism.

19. Single strand break
 Most likely efficiently repaired, with little, if
any , long term consequences to the cell.
Double strand break
Difficult for the cell to repair. They show
reasonable corelaiton with cell killing. If repair
does not take place, the DNA chains can separate,
with serious consequence to the life of the cell.

20. SINGLE STRAND BRAKES
RELATIVELY
INCONSEQUENTIAL IN
TERMS OF CELL
KILLING. WILL BE
EFFICIENTLY REPAIRED
, WITH LITTLE, IF ANY,
LONG TERM
CONSEQUENCES TO
THE CELL

21. DOUBLE STRAND BRAKES
VERY DIFFICULT FOR THE
CELL TO BE REPAIRED.
CAN LEAD TO CELL
KILLING. IF REPAIR
DOESN’T TAKE PLACE,
THE DNA CHAINS CAN
SEPARATE. SERIOUS
CONSEQUENCE TO CELL
LIFE.

22. Base damage
 The loss or a change of a base on the DNA
chain results in the alteretion of the base
sequence. Base sequence stores and
transmits genetic information. It has
nmajor consequences. Loss or change of
base is considered a type of mutation.

23. EXAMPLES OF MUTATIONS

25. Radiation syndrome
 Hematopoietic Syndrome
 •Prodromal Stage: Mild symptoms appear
within a few hours and last for several days
 •Latent Period: May last up to 4 weeks
 •Manifest Illness: Vomiting, diarrhea,
fatigue and fever – Decline in blood cells –
Recovery in 2 to 4 weeks…May last up to 6
months
 •Possible death due to infection,
dehydration or hemorrhage

26. Gastrointestinal Syndrome
•Prodromal Stage: Vomiting and diarrhea occur
within hours and last up to one day
•Latent Period: Lasts 3-5 days
•Manifest Illness: Nausea, vomiting and diarrhea –
Worsens to bloody stools
•Death within 4 to 10 days after exposure primarily
due to intestinal cell damage – Also damage to
blood-forming tissue results in hemorrhaging and
dehydration.

27. Central Nervous System Syndrome
•Prodromal Stage: Severe nausea and vomiting within a few
minutes – Nervousness, confusion, burning skin, vision loss,
possible loss of consciousness
•Latent Period: May last up to 12 hours, or not at all
•Manifest Illness: Disorientation, loss of muscle control,
breathing problems, seizures, coma
•Death within a few days of exposure – due to increased fluid
in brain (pressure) – Death occurs before hematologic and
gastrointestinal symptoms appear

28. Total Body Response to
Radiation
 Acute Radiation Syndrome – full body exposure
given in a few minutes.
 3 stages of response:
1. Prodromal Stage: NVD stage
(nausea, vomiting, diarrhea)
2. Latent Period: Feels well while
undergoing biological changes
3. Manifest Stage: Full effects felt,
leads to recovery or death

29. 3 Acute Radiation Syndromes
Early Effects
•
•
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Bone marrow syndrome: results in infection,
hemorrhage & anemia
Gastrointestinal syndrome: results in diarrhea,
nausea & vomiting, fever
Central nervous syndrome: results in convulsions,
coma, & eventual death from increased intracranial
pressure.
CNS least sensitive in ADULTS –
MOST sensitive in the FETUS

30. 3 Acute Radiation Syndromes
Early Effects
•
•
•
Bone marrow syndrome: results in infection,
hemorrhage & anemia
Gastrointestinal syndrome: results in diarrhea,
nausea & vomiting, fever
Central nervous syndrome: results in convulsions,
coma, & eventual death from increased intracranial
pressure.
CNS least sensitive in ADULTS –
MOST sensitive in the FETUS

31. Total Body Response to
Radiation
 Acute Radiation Syndrome – full body exposure
given in a few minutes.
 3 stages of response:
1. Prodromal Stage: NVD stage
(nausea, vomiting, diarrhea)
2. Latent Period: Feels well while
undergoing biological changes
3. Manifest Stage: Full effects felt,
leads to recovery or death

32. DOSE LIMITS
 State Annual Limits
 Occupationally Exposed Workers 5 rem/yr
whole body, gonads
 15 rem/yr lens
 Non-occupationally exposed worker (and the
general public) 0.1 rem /yr (100 mrem)

33.  Limit embryo/fetus dose equivalent to 500
mrem (0.5 rem) total.
 2. Once a pregnancy becomes known limit
embryo fetus dose equivalent to 50 mrem per
month, excluding medical exposure

34. THANKS