Physics of radiation therapy

Physics of radiation therapy
أستاذ المادة : المدرس ناهدة حمود الجراح
-Brachy therapy
-LD50
-Rad
-Roentgens
-Gray
Brachy therapy:-
A short distance therapy .Radium source is put into or on
the surface of tumors.
Advantage: - of brachy therapy is that gives a very
large dose to the tumors with minimum radiation
to the surrounding tissue.
Disadvantage:-is the non-uniformity of the dose
since the radiation is much more intense near the
source .Concerns radiation safety .The therapist is
close to the source and to the patient(another
source).
Physics of radiation therapy:-
There is evidence that an error of (5-10)% in
radiation dose to tumor can have a significant
effect on the results of the therapy .Too little
radiation does not kill the entire tumor;while too
much can produce serious complications in normal
tissue.
The basic principle of radiation therapy is to
maximize damage to the tumor while minimizing
damage to normal tissue.This is generally
accomplished by directing a beam of radiation at
the tumor from several directions, so that the
maximum dose occurs at the tumor.
Physics of radiation therapy
أستاذ المادة : المدرس ناهدة حمود الجراح
Some normal tissues are more sensitive to radiation
than others. Ionizing radiation ,such as x-rays and
?-rays, tearing electrons off atoms to produce
(+ve)and (-ve)ions.
It also breaks up molecules; the new chemicals
formed are no use to the body and can be
considered a form of poison.
The units are used to measure the amount of
radiation to the patient:-
1-Erythematic dose :- the quantity of x-rays that
caused redding of the skin.
2-Exposure (Roentgens (R) ),see ch16.4
1R=2.58?10-4 c/kg of air.
3-Absorbed dose (rad).The (rad) is defined as 100
ergs/g. that is a radiation beam that gives 100ergs
of energy to 1g of tissue an absorbed dose of 1(rad)
or gray =100(rad).
The (rad) can be used for any type of radiation
in any material;the roentgen ( R ) is defined only
for x-rays and ?-rays in air.
RBE(Relative Biological Effect)
The ratio of the number of gray of 250 KVp x-rays
needed to produce a given biological effect to the
number of grays of the test radiation needed to
produce the same effect.
LD50:-
The quantity of radiation that will kill half of the
organisms in a population (cells,mice,people,……etc)
is called the lethal dose for 50% or LD50.
Physics of radiation therapy
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LD50/30 Kill 50%in 30days
LD50 kill 50%
Surviving %
LD50
Oxygen effect:-tumor cell is high resistance to radiation
without oxygen and it is more sensitive to radiation with
oxygen. So that if you treat the cancer cell by radiation
you should treat it by oxygen firstly to become sensitive
to radiation and this reduce the does is used.
100
Dose(Gy)
1 2 3 4 5 6 7
5
1
0.2
X?rays or ??
rays
? ?particles
50
Physics of radiation therapy
أستاذ المادة : المدرس ناهدة حمود الجراح
Summary:
Brachy therapy is short distance therapy and it has
advantages and disadvantages. LD50 is the lethal does to
killfifty percent of cells exposed to radiation.