37406246 radioactivity radioisotopes
TRANSCRIPT
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Dr Saurabh
Samdariya
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I. IntroductionII. Historical aspects
III. Sources
IV. Ionising radiations
V. Decay constant
VI. activity
VII. half life
VIII. radioactive seriesIX. radioactive equilibrium
X. modes of radioactive decay
XI. Introduction to radioisotopes
XII. radioisotopes in clinical medicine
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the property of an element wherein atom gives off
radiation in terms of particle, electromagneticradiation or both in order to achieve stability is
called as radioactivity & the process is called as
radioactive decay/disintegration.
Total 118 elements discovered till now
Most of them are stable
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Naturally occuring radioactive elements
Uranium
grouped into 3 series Actinium
Thorium
U238 4.51 x 109
yr Pb206
U235 7.13 x 108 yr Pb207
Th23 21.39 x 1010 yr
Pb208
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HISTORICAL ASPECTS
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William
ConradRoentgen
Discoveryof x
Rays - 1895
Nobel prize-1901
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Ernest Rutherford
Discovery of alpha
particles
(1897)
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Sir Joseph john
Thomson
Discovery of electrons
Nobel prize-1906
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Paul ulrich vilard
Discovery of
gamma rays-1900
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Sir James Chadwick
Discovery of neutron
Nobel prize-1932
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1.naturally occuring-Radon
Pottasium
Carbon-14
2. manmade - Medical uses
Consumer products( smoke
detectors)
Fall out from nuclear testing
Emissions (nuclear plants)
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POSITIVECHARGE
PROTONS
NEUTRALCHARGE
NEUTRONS
NUCLEUS
NEGATIVE CHARGE
ELECTRONS
ATOM
Most of the atoms mass.
NUCLEUS ELECTRONS
PROTONS NEUTRONS NEGATIVE CHARGE
POSITIVECHARGE
NEUTRALCHARGE
ATOM
QUARKSAtomic Number
equals the # of...
equal in a
neutral atom
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Atomic Mass Unit (amu)is defined as exactly 1/12 of the mass of the atom
of Carbon-12. It is a very small number.
Isotopes An atom of an element that has the same atomic number butdifferent mass number is called an isotope.
Ions When an atom loses or gains electrons, the species formed is calledan ion and carries a net charge
The atomic massof an element is the average of the isotopic masses,
weighted according to the naturally occurring abundances of the isotopesof the element.
The molecular weight is the sum of amu for all elements, in the molecule,
times Avogadros number (a very large number, 6.02*1023), in grams
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Four Primary Types Of Ionising Radiations-
1. Alpha particles
2.Beta particles3.Gamma rays (or photons)
4.X-Rays (or photons)
5.Neutrons
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Composed of two protons and twoneutrons
Particle radiation (largest and mostmassive of all the ionizing particles)
Least penetrating of all ionizing radiationand can be shielded by a few inches ofair, penetrating power can be stopped by
a piece of paper or the outer layer ofskin.
It has a very short range and it has greatdestructive power within its short range.
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Alpha emission ctdIt is not suitable forradiation therapy since
its range is less than atenth of a millimeterinside the body.
Its main radiation hazardcomes when it is ingestedinto the body it ispositioned for maximumdamage when in contact
with fast-growingmembranes and livingcells
BETA RADIATION
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BETA RADIATION
Particle radiation Beta particles are just electrons from the nucleusThe high energy electrons have greater range ofpenetration than alpha particles, but still much less than
gamma rays. The radiation hazard from betas isgreatest if they are ingested. can be shielded by several inches of plastic, thin
plywood and sheet metal. Can penetrate up to 1/4 in. into the tissue
G di i i
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Gamma radioactivity
is composed of
electromagnetic rays; hasno mass
distinguished from x-raysonly by the fact that itcomes from the nucleus
Most gamma rays aresomewhat higher in energythan x-rays and therefore
are very penetrating.
G di i i
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thick concrete can reduce
the effect of gamma raysto permissible levels.
It is the most usefultype of radiation formedical purposes, but atthe same time it is themost dangerous becauseof its ability to penetratelarge thicknesses of
material
Gamma radioactivity
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Fraction of total no of atoms that decay per unit of
time
Radioactive decay is a stastical phenomenon
No of atom disintegrating per unit time-no ofradioactive atoms present
N N
T
N = No e-t
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Radioactivity of radioactive elements
A = - N
A = Ae- t
units - curiebecqurel(SI)
1 ci =3.7x10 dps
1 Bq = 1 dps=2.7x 10-11 ci
y
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Time required for either the activity or no of radioactive
atom to decay to half of the initial value
N = Noe- t
T1/2 =
.693
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Physical Half-Life
Time (in minutes, hours, days or years) required for the activity of a radioactive material to decrease by one half due
to radioactive decay
Biological Half-Life Time required for the body to eliminate half of the radioactive
material (depends on the chemical form)
Effective Half-Life
The net effect of the combination of the physical & biological
half-lives in removing the radioactive material from the body
Half-lives range from fractions of seconds to millions of years
1 HL = 50% 2 HL = 25% 3 HL = 12.5%
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Avg life time for decay of radioactive atoms
Time period that a hypothetical source would need if it
retained its original activity for the time period and then
suddenly decayed to zero activity to produce the same no
of disintegration as produced over an infinite time period
by the source if it decayed exponentially
ta = 1/
ta = 1.44 t1/2
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Activity per unit mass of radionuclide
Uses -
1.Tracer studies are done using high
sp. activity elements.2.Teletherapy source(Co-60 is preferred
overCs-137)
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parent nuclei daughter nucei
(t1/2)p> (t1/2)d {Transient eq.}
(t1/2)p>>>>>(t1/2)d {Secular eq. }
examples-
- Mo generator producing Tc99m for
diagnostic purposes (transient)
- Ra source in a sealed tube or needle
in order to keep radon gas (secular)
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A = A1 x y2 [ ( 1-e-y2-y1 ) t ]y2-y
1
A2 / A1 = Y2 / Y2-Y1 = T1 / T1-T2
A2 = A1 (1- e-y2
t )
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An unstable releases energy to become morestable(RADIOACTIVE DECAY)
decay
primay decay processes decay
e capture
emission
Secondary decay processes iso metastbleinternal conversion
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3000 known nuclei, but only266 stable ones!
Z > 83 elements not stable!
Tendency forN Z, for smallZ, but N > Z for larger Z.
(due to proton repulsion)
Unusual stability formagic numbers.Z, N = 2, 10, 18, 36, 54
(analogous to electronic shells
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Radioactivity
decays with time
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particles are monoenegertic and have 4 to 8 Mevenergy.
ZXA
Z- 2YA-4 + 2He
4 + Q
Q = Disintegration energy(K.E. of alpha particle
and daughter nuclei)
Ex- elements having high Z (Ra216 Rn222 Po218
U235 Pu239 Am241)
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1.
-
(negatron)
decay- high n/p ratioEx.- H, C, P, Co, Sr, Mo, I,
Cs, Au
0n1 1p1 + -1 0 + + Q
ZX
A
Z- 1Y
A
+ -1
0
+ +Q
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2 . + (positron)decay- low n/p ratio( )
1p
10n
1 + +10 + + Q
Z
XA
Z- 1
YA ++1
0 +
+Q
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Similar to + decay
nucleus captures e- from its orbit (usually K shell )
It increases nuclear mass by .511 Mev
From p to n
Occur for not sufficient energy for b+decay(1.22Mev)
Ex - Na, K, Cr, Co, Ir
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Secondary decay processes-
1. emission
. excitation energy given off by
photon = rays
. fast process
E = EP - ED
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Ionizing Radiation
alpha particle
beta particle
Radioactive Atom
X-ray
gamma ray
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if two atoms of an element are having same atomic no
(p) but differ in their their atomic mass(A) then those two
atoms are called as isotope of each other and if atom is
having property of radioemission it is called as
RADIOISOTOPES.
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DIAGNOSIS THERAPY
in vitro in vivo internal external
Systemic sources tele radio
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14C
3H
125I
201Tl123I
111In
67Ga
81Rb-81mKr
others
+ emitters
for PET
18F, 11C,13N,15O
86Y, 124I
68Ge-68Ga
82Sr-82Rb
131I,90Y153Sm,186Re
188W-188Re
166Ho,177Lu,
Others
a-emitters:225Ac-213Bi
211At,223Ra
149Tb
e--emitters:125I
sealed sourcesand
applicators:
192Ir,
182Ta,
137Cs
Others
needles for
brachytherapy:
103Pd,
125I
microspheres
90Sr or 90Y,
others
60Co
Gamma
Knife
137Cs
blood
cell
irradi-ation
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Radioactive traccers which emmit gamma rays
within the body are given by injection inhalation or
orally
Radioactive tracers are short lived isotopes linked
to chemical compounds which permit speciic
physiological processes to be scrutinised
Emitted gamma rays are detected by gamma
camera & build image from the point from whichradiationis emitted.image is enhanced by computer
& viewed on monitor..
thus a organ can be viewed from
several angles
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now a days PET & PETCT are also used instead of gamma
camera.. They detects positrons emitted from
radionucleides
FUNCTIONAL imaging
Mean effffective dose is 4.6 mSv per diagnostic procedure
Advantage over routine x ray imaging-
1.both bone & soft issue can be imaged successfully
2.functional status of organ is determined
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2 forms
teletherapy/EBRT
(external RNT)
brachytherapy
(internal RNT)
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The imaged property is the distribution of radionuclide-
labeled agents injected in the body: radiopharmaceuticals
Produce functional images of tracer concentrations relatedto pathophysiological Process
Radioisotope- An unstable isotope of an element thatdecays or disintegrates spontaneously, emitting radiation
Radioactive decay of radioisotopes leads to the emission of-, -, -, and x radiation depending on the radionuclideinvolved
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The range of-, -particles is small
for in vivo imaging using external
Radioisotope imaging is restricted to the use of radionuclides emitting photons with energies > 50 keV
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Anger camera (1960s)
Radioisotope imaging is restricted to the useof radio nuclides emitting photons
with energies > 50 keV
Lead collimator (incidence orientationselection)
Scintillation camera of NaI (sodium iodide) Photomultipliers (PMT)
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Static planar scintigraphy
Dynamic planar scintigraphy
Emission Computed Tomography (ECT)
Single Photon Computed Tomography (SPECT) Positron Emission Tomography (PET
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Single Photon Computed Tomography (SPECT) Same principle of Gamma camera but with 2 or 3 rotating
cameras to record projection data more efficiently
In CT we know the position of the emitting source and thedetection point; in SPECT only the detection point
In CT absorption is the essence of the imaging process; inSPECT attenuation degrades the images
Attenuation must be compensated for (single scan-line of
photons to estimate transmission coefficient)
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Gated SPECT particularly useful in cardiacperfusion studies
Some systems with slip ring technology
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Radiotracer produces positrons, which areannihilated within around 1mm from their origin
After annihilation 2 -ray photons are emittedalong a Line Of Response (LOR)
Electronic coincidence detectors (12ns), which
eliminates lead collimators and allows higherefficiency
In PET it is easier to correct for attenuation
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AUGER electron emitters for therapy
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+ emitters
for
in vivo dosimetry
Scintigraphic abdominal
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images 5 & 24 h p.i.
affected by
carcinoid with
extensive hepatic and
paraaortal metastases
Patients:
3 patients with metastases of
carcinoid tumor (histologicallyconfirmed)
. No therapy with unlabeled
somatostatin > 4 weeks
Age: 46 67 years, male
All were candidates for a
possible 90Y-DOTATOC therapy
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PhysicalRadionuclide Half-Life Use__________________Americium-241 432 yrs Smoke Detectors
Bismuth-213 46 min TAT(targeted alpha therapy)
Cesium-137 30 yrs Food Irradiator
Cobalt-60 5.27 yrs EBRT,sterilising
Cromium-51 28 days label RBC & quantify GI protein loss
Dysprosium-165 2hr aggregated OH in synovectomy
Erbium-169 9.4 days arthritis pain-synovial joints
Holmium-166 26 hr liver tumors(,Rx)
Hydrogen-3 12 yrs Exit Signs
Iridium-192 74 days Industrial Radiography,BT wires
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Physical
Radionuclide Half-Life UseIodine-125 60 days Brachtherapy(prostate,brain)
- DVT leg, GFR kidney
Radioimmunoassys
Iodine-131 8 days Imaging & treating throid cancer,- abnormal liver function ,
renal blood flow
urinary tract obstruction
Iron-59 46 days Study Fe metabolism in spleen
Lutetium-177 6.7 days Rx of small endocrine tumors
Molybdenum-99 66 hr PARENT in generator for Tc99m
Palladium-103 17 days prostate ca-BT permanent seed implant
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Physical
Radionuclide Half-Life Use______________________Phosphorus-32 14 days Rx of Polycythemia vera
Plutonium-239 24,000 yrs Nuclear Weapon
Pottasium-42 12 hr Detemination of exchangeable
pottasium in coronary blood flow
Radon-222 4 days Environmental Level
Rhenium-186 3.8 days pain reief in bone caner
Rhenium-188 17 hr -iradiate coronary arteries from
an angioplasty baloon
Samarium-153 47 hr pain relief in metastatic bone 20
Selenium-75 120 days study production of digestive
enzymes (Selenomethionine)
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Physical
Radionuclide Half-Life Use______________Sodium-24 15 hrs study electrolytes in body
Strontium-89 50 days relief from pain of prostate
& bone cancerStrontium-90 29 yrs Eye Therapy Device
Technetium-99m 6 hrs Diagnostic Imaging
(skeleton,myocardium,lung)
Xenon-133 5 days lung ventilation studiesYtterbium-169 32 days CSF studies
Ytterbium-177 1.9 hrs progenitor ofLu-177
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Physical
Radionuclide Half-Life Use_________________________
Fluorine-18 PET(brain,heart physiology,pathology)
Cobalt-57 272 days marker to estimate organ size
Gallium-67 78 hr tumor imaging, localisation of
inflammatory leison(infective)
Gallium-68 68 min positron emitter(PET)
Iodine-123 13 hr of thyroid function .
Thallium-20173 hr of CAD , MI
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allow to separate chemically short-lived radioactive daughter nuclei with
good characteristics for medical
imaging from long-lived radioactive
parent nuclei. Typical techniques used
are chromatographic absorption,
distillation or phase separation
This method is in particular applied forthe separation of the rather short-lived99Tcm (T1/2=6 h) from the long lived
99Mo
(T1/2=2.7 d).
Milking cow analogy
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Applying the radioactivedecay law the growth of
activity of the daughter
nuclei A2 with respect of
the initial activity of themother nucleusA1
0can
be expressed in terms of
their respective decay
constants 2 and 2 with
2 >> 1:
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52-year old female breast cancer
ANT POST
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Phosphorus-32
Rhenium-186
Samarium-153
Strontium-89
Rhenium-188
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Gadolinium enhanced
SPECT imageRadioisotope
cisternography
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