10 2.ppt, Fizyka jądrowa, Dozymetria
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of maximum energy loss of radiation, the
number of secondary ionizations products peaks which in turn
At the position
d
max
max
of maximum energy loss of radiation, the
At the position
number of secondary ionizations products peaks which in turn
maximizes the dose at that location.
maximizes the dose at that location.
The dose is denned (see section on dosimetry) as total energy loss of
radiation per mass. It can be formulated in terms of the activity
The dose is denned (see section on dosimetry) as total energy loss of
radiation per mass. It can be formulated in terms of the activity
A(t)
A(t)
(number of
(number of
incident particles/second in cases of external beam treatment
N(t)
N(t)
)
)
and energy loss
and energy loss
incident particles/second in cases of external beam treatment
or stopping power
dE/dx.
of irradiation
is expressed in terms of number of particles N(t), total amount of energy lost
dE/dx.
The total absorbed dose
The total absorbed dose
D(t)
D(t)
after a period
after a period
t
t
of irradiation
or stopping power
is expressed in terms of number of particles N(t), total amount of energy lost
E
R
,
,
and irradiated area A:
with m, V, and
as mass, volume, and density of the exposed organs. This
as mass, volume, and density of the exposed organs. This
results in a absorbed dose
with m, V, and
results in a absorbed dose
D(t,d)
D(t,d)
after an irradiation period
after an irradiation period
t
t
at a certain depth
at a certain depth
d:
d:
The absorbed dose at a certain depth
d
d
is directly
is directly
The absorbed dose at a certain depth
proportional to the stopping power
1/
1/
dE/dx
dE/dx
!
!
proportional to the stopping power
100%
A
A
75%
75%
Within the area
A
A
each point at a certain depth
each point at a certain depth
d
d
receives
receives
Within the area
the same dose
ISODOSE.
ISODOSE.
the same dose
The average dose due to energy loss of
radiation within
radiation within
The average dose due to energy loss of
a depth
d
d
over a period
over a period
t
t
is:
is:
a depth
The dose is directly proportional to the transfer
and absorption coefficients which change with depth.
The dose is directly proportional to the transfer
and absorption coefficients which change with depth.
[cm
2
2
/g]
[cm
/g]
The dose distribution is less well defined compared to particle beams.
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