Molecular and Cellular Radiation biology
Ionizing Radiation and the Human body

From x-rays, gamma, or high energy
particulate radiation
◦ ALPHA, BETA
◦ Alpha=two protons and two neutrons attracts
negatively charged electrons

Ionized atoms will not bond properly in
molecules

LET

RBE

OER




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
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X-ray/gamma rays
Streams of particles
with no mass or charge
Penetrating
Sparsely ionizing
Interacts randomly
Damage via indirect
action
Sublethal damage



Particles of mass and
charge
Alpha, neutrons
What other
characteristics?

Low


High

◦ Risk of damage to
DNA/Probability of
interaction with DNA
◦ What radiations are
considered low LET?
◦ Risk of damage to
DNA/ DNA/Probability
of interaction with
DNA
◦ Internal contamination
◦ What radiations are
considered high LET?

250 kVp of known
radiation (usually xray) over dose of test
radiation=biologic
effect (Box 5-2)
Used in animals
Weighting factor of
radiation used to
determine biologic
damage


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
DOSE REQUIRED TO PRODUCE AN EFFECT IN
AN OXYGEN DEPRIVED ENVIRONMENT VS A
NORMAL OXYGEN ENVIRONMENT
OER IS HIGH FOR LOW LET
THE OPPOSITE FOR HIGH LET
THE DIFFERENCE IS DUE TO DIRECT AND
INDIRECT EFFECT
BOTTOM LINE…..IF IONIZATION FROM EITHER EFFECTS
DISTURBS THE CHEMICAL BALANCE OF THE CELL, THE
CELLULAR ACTIVITY BECOMES ABNORMAL OR THE CELL
CAN EVEN CEASE TO FUNCTION


IMPACTS THE DNA
OCCURS MORE
OFTEN WITH HIGH
LET



INTERACTS WITH
WATER
OCCURS MORE
OFTEN WITH LOW
LET
RADIOLYSIS OF
WATER/FREE
RADICALS

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SINGLE STRAND BREAK figure 6.6
DOUBLE STRAND BREAK figure 6-7/IN SAME
RUNG figure 6-8
MUTATION figure 6-9
COVALENT CROSS LINKS figure 6-10
CHROMOSOME BREAKS
CHROMOSOMAL FRAGMENTS
CHROMOSOME ANOMALIES
Structural changes

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

HIGHLY MITOTITIC
ABNORMALLY DIVIDE
LARGE NUCLEUS
Relate this to Bergonie and Tribondeau (pg
102) and direct/indirect effects
THE MASTER MOLECULE
PG 125