2. • Definition
• Units associated with measurement of
radiation
• Harmful effect of radiation on human body
3. Radiation
• Radiation is the emission or transmission
of energy in the form
of waves or particles through space or through
a material medium.
• Packet of energy
5. Ionizing radiation
• Radiations that carries enough energy to
free electrons from atoms or molecules,
thereby ionizing them.
• Causes change in the chemical bond or
formation of charged particle
6. NON IONIZING RADIATION
• Radiations that does not carries
enough energy
to free electrons from atoms or molecules.
• It has sufficient energy only for excitation, the
movement of an electron to a higher energy
state.
10. RADIOBIOLOGY
• The branch of biology concerned with the
effects of ionizing radiation on organisms and
the application in biology of radiological
techniques.
11.
12. G1 phase (growth)
• The first phase - From the end of the previous
M phase until the beginning of DNA synthesis
is called G1.
• The duration of G1 is highly variable, even
among different cells of the same species.
13. S PHASE
• starts when DNA synthesis commences;
• when it is complete, all of
the chromosomes have been replicated, i.e.,
each chromosome has two chromatids.
14. G2 phase
• G2 phase occurs after DNA replication and is a
period of protein synthesis and rapid cell
growth to prepare the cell for mitosis.
• Second most sensitive phase to radiation
15. MITOSIS
• Mitosis is the process by which a eukaryotic
cell separates the chromosomes in its cell
nucleus into two identical sets in two nuclei
• The cells are most sensitive to radiation during
mitosis.
16. Radiation damage
• 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.
17. There are two mechanism by which
radiation causes cellular damage
• DIRECT EFFECT –Ionizing radiation interact
with the DNA and causes damage
• INDIRECT EFFECT-interact initially with water
molecule and as a result free radicals are
formed, causing cellular damage.
19. Indirect Action in Detail
• H2O -> H2O+ + e-
• H2O+ 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
20.
21. DNA DAMAGE
• 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.
22. • If repair does not take place, the DNA chains
can separate, with serious consequence to the
life of the cell.
24. Double strand brake
•VERY DIFFICULT
FOR THE CELL TO
BE REPAIRED.
•CAN LEAD TO
CELL KILLING.
• SERIOUS
CONSEQUENCE
TO CELL LIFE.
25. Base damage
• The loss or a change of a base on the DNA
chain results in the alteration of the base
sequence.
• Base sequence stores and transmits genetic
information.
• It has major consequences. Loss or change of
base is considered a type of mutation
28. We quantify radiation in terms of
three category
1. RADIATION IN AIR(EXPOSURE)
2. RADIATION IN TISSUE
3. EFFECT IN TISSUE
29. Radiation in air
• Exposure-it is defined as the number of ions
created by photons in air.
• Unit is Roengten.
• International unit is coulomb/kilogram (C/kg)
30. How much radiation is entering our
body?
Radiation absorbed dose
• Absorbed dose indicates the amount of energy deposited
by interacting ionization radiation (X-rays, gamma rays,
electrons, beta, neutrons, alpha, protons, all radiation) with
unit mass of matter.
• Absorbed dose = Amount Mass of energy deposited
mass of matter
• The unit of absorbed dose is Joule per Kilogram (J kg–1) and
a special name has been given to this in SI unit is Gray.
• Traditional unit is called RAD
31. Effect in human body
Equivalent Dose
• Equivalent dose may also be called radiation protection
unit as it takes into account the potential of the
radiation to cause biological damage .
• The ability to cause biological damage (effectiveness)
varies with the type of radiation and is closely related
with its ionizing capability .
• The traditional unit for equivalent dose is Rem and the
SI unit is Sievert (Sv).
33. Biological effects of ionizing radiation divided into 2 major
categories:
Deterministic effects:
• This type of radiation damage is related to high dose, short
period exposure
• The basic properties of deterministic radiation are:
• The severity of the effect depends on absorbed dose
• There is a threshold dose below which effects do not occur
• eg-cataract, infertility, burns, radiation sickness etc
34. Stochastic effect
• This type of radiation damage is related to low-level, long
term exposure to radiation.
The basic properties of stochastic radiation are:
• The probability of the effect occurring depends on the
absorbed dose
• The severity of the effect is independent of the absorbed
dose
• There is no dose threshold
• This means that if you are exposed to large doses it makes the
effect more likely to occur but does not increase the severity
of the effect.
35. 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)
36. • This also means that a developing embryo is most sensitive to radiation during the
early stages of differentiation, and an embryo/fetus is more sensitive to radiation
exposure in the first trimester than in later trimesters
• Blood-forming organs
• Reproductive organs
• Skin
• Bone and teeth
• Muscle
• Nervous system
sensitivity
37. Factors Influencing Biological Effect
• Total absorbed energy (dose)
• Dose rate
– Acute (seconds, minutes)
– Chronic (days, years)
• Type of radiation
• Source of radiation
– External
– Internal
38. • Time since exposure
• Area or location being irradiated
• Age at exposure
39. Acute Radiation Syndrome
A collection of signs and symptoms
experienced by persons after acute whole-
body exposure to radiation.
• Acute Radiation Syndromes include
– Hematopoietic Syndrome
– Gastrointestinal Syndrome
– Cardiovascular and Central Nervous System
Syndrome
40. Hematopoietic Syndrome
• Whole-body exposures of 2 to 7 Gy cause injury
to the hematopoietic stem cells of the bone
marrow and spleen.
• Bone marrow is a highly radiosensitive tissue due
to the high mitotic activity of these cells & the
presence of many differentiating cells.
• Doses in this range cause a rapid and profound
fall in the numbers of circulating granulocytes,
platelets, and finally erythrocytes
41. • Mature circulating granulocytes, platelets, and
erythrocytes themselves are very radioresistant
• However, since they are nonreplicating cells, paucity in
the peripheral blood after irradiation reflects the
radiosensitivity of their precursors
• Rate of fall in the circulating levels of a cell depends on
the life span of that cell in the peripheral blood
• Granulocytes, short lives in circulation, fall off in a
matter of days,
• Red blood cells, long lives in circulation, fall off only
slowly
42. • Clinical signs of the hematopoietic syndrome
include infection (in part from the lymphopenia
and granulocytopenia), hemorrhage (from the
thrombocytopenia),and anemia (from the
erythrocyte depletion).
• Individuals may survive exposure in this range if
the bone marrow and spleen recover before the
patient dies of one or more clinical complications.
• Death results from the hematopoietic syndrome,
usually occurs 10 to 30 days after irradiation
43. GASTROINTESTINAL SYMPTOMS
• Whole-body exposures in the range of 7 to 15
Gy cause extensive damage to the
gastrointestinal system.
• Such exposure causes injury to rapidly
proliferating basal epithelial cells of the
intestinal villi and leads to a loss of the
epithelial layer of the intestinal mucosa.
• Turnover time for cells lining the small
intestine is normally 3 to 5 days.
44. • Because of the denuded mucosal surface, plasma
and electrolytes are lost therefore efficient
intestinal absorption cannot occur. Ulceration
also occurs, with hemorrhaging of the intestines.
• All these changes are responsible for the
diarrhea, dehydration, and loss of weight.
• Endogenous intestinal bacteria readily invade the
denuded surface, producing septicemia.
• Death occurs before the full effect of the
radiation on hematopoietic systems can be
evidenced
45. • The combined effects on these stem cell
systems cause death within 2 weeks from a
combination of factors that include :
fluid and electrolyte 'loss' infection
possibly nutritional impairment
46. CARDOVASCULAR AND CNS
SYMPTOMS
• Exposures in excess of 50 Gy usually cause death
in 1 to 2 days.
• The few human beings who have been exposed at
this level showed collapse of the circulatory
system with a precipitous fall in blood pressure in
the hours preceding death.
• Autopsy revealed necrosis of cardiac muscle
• Victims also may show intermittent stupor,
incoordination , disorientation, and convulsions
suggestive of extensive damage to the nervous
system.
47. CANCER ASSOCIATED WITH RADIATION
• Radiation causes cancer by modifying DNA.
• Radiation induced gene mutation.
• Radiator acts as initiator (it induces change in
the cells so that it no longer undergoes
terminal differentiation) and also promoter (
stimulating cells to multiply ).
48. LEUKEMIA
• The most common cancer
• The incidence of leukaemia rises after
exposure of the bone marrow to radiation.
• Leukaemia's appear sooner than solid tumors
because of the higher rate of cell division and
differentiation of hematopoietic stem cells
compared with the other tissues.
• Persons younger than 20 years are more at
risk than adults.
49. • Brain and nervous system CA
• Thyroid CA
• Esophageal CA
• Salivary gland CA
