1 Common Lab Sources. 2 Radioactive Sources 3 Radionuclides in the AZ Particle Lab Gamma 60 Co @...
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Transcript of 1 Common Lab Sources. 2 Radioactive Sources 3 Radionuclides in the AZ Particle Lab Gamma 60 Co @...
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Radionuclides in the AZ Particle Lab
Gamma 60Co @ 1uC 241Am, 133Ba, 137Cs, 60Co, 88Y, 22Na, 64Mg,
203Hg, 57Co @ 10 uC
X-ray 55Fe
5.90 keV (24.4%) and 6.49 keV (2.86%)
Beta 90Sr/90Y @ 50 mCi, 5 mCi, 2mCi, 0.5mCi
Alpha 241Am @ 5 mCi
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Radionuclides in Medicine Nuclear medicine
Diagnostic Permits functional imaging (biochemistry and
metabolism versus anatomical structure) >80% of all procedures use 99mTc
Radiotherapy Therapeutic
Primarily for cancer treatment External beam – teletherapy using 60Co units Internal – brachytherapy using small, encapsulated
sources
Notes 90% of all radionuclide use in medicine is diagnostic Use of term “radioisotope” is common Will there be a shortage of radionuclides in the
future?
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Radionuclides in MedicineGeorge de Hevesy
Nobel in 1943 for use of isotopes as tracers for chemical processes A failed experiment to separate Radium-
D (210-lead) from lead (206-lead) The landlady’s leftovers
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Radionuclides for Diagnosis
What are the characteristics of an ideal radionuclide for diagnosis? Half-life?
Effective half-life 1/eff = 1/radioactivity + 1/biological
Type and energy of radiation? Production and expense? Purity? Target area to non-target ratio?
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Radionuclides for Diagnosis
The ideal gamma energy (for gamma camera use) is between 100 and 250 keV
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Nuclear Medicine99mTc is used in ~ 80% of diagnostic
procedures 99mTc pertechnetate (TcO4
-) is mixed with an appropriate pharmaceutical (biological construct) for use for Cardiac imaging and function Skeletal and bone marrow imaging Pulmonary perfusion Liver and spleen function Cerebral perfusion Mammography Venous thrombosis Tumor location
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Technetium – 99mA closer look
There is no 1 emission, it IC’s
IC competes with 2
IC competes with 3
X-ray and Auger electron emission can also occur
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Radionuclides for TherapyBrachytherapy
Brachys = short Brachytherapy uses encapsulated
radioactive sources to deliver a high dose to tissues near the source Provides localized delivery of dose But the tumor must be well localized and small
Proposed by Pierre Curie and, independently, Alexander Graham Bell shortly after the discovery of radioactivity
Inverse square law determines most of the dosimetric effect
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Brachytherapy
Used to treat a variety of cancers Prostate Gynecological Eye Skin
Only ~10% of radiotherapy patients are treated via brachytherapy
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BrachytherapySources
Most of the sources used emit gammas Lower gamma energies are preferred for
radioprotection
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Brachytherapy
Sources But a few emit betas
90Sr/90Y for eye lesions 90Sr/90Y , 90Y, 32P for preventing restenosis
after angioplasty
In general, alphas and betas are absorbed by encapsulation to avoid tissue necrosis around the source
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BrachytherapySources
226Ra -> 222Rn + -> … -> 206Pb
Although rarely used now, it’s a good reaction to know given its historical significance
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BrachytherapySources
226Ra -> 222Rn + -> … -> 206Pb Which equilibrium is achieved (t1/2(226Ra) =
1600 years)? 222Rn is a radioactive gas About 50 gamma energies are possible
ranging from 0.184 to 2.45 MeV, though on average there are 2.2 gammas emitted for each decay
The average energy (filtered by 0.5 mm of Pt) is 0.83 MeV
The exposure rate constant (assuming 0.5 mm of Pt) is = 8.25 R-cm2/hr-mCi
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BrachytherapySources
More modern replacements for 226Ra are 137Cs Familiar gamma ray spectrum with
E=0.662 MeV t1/2=30 yrs and =3.26 R-cm2/hr-mCi
and 192Ir More complicated gamma ray spectrum
with <E> = 0.38 MeV t1/2=73.8 days and =4.69 R-cm2/hr-mCi
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Brachytherapy
Methods of delivery LDR (0.4-2 Gy/hr) versus HDR (> 12
Gy/hr) Temporary versus permanent Intracavity versus interstitial
Also surface, intraluminal, intravascular, intraoperative
Seeds, needles, tubes, pellets, wire
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Radionuclide Production
How are radionuclides made? Primary sources
Nuclear reactors 235U fission produced Neutron activated Both produce neutron rich radionuclides
Cyclotrons Uses charged particle beams (p, d, t, ) Produces proton rich radionuclides
Secondary source Radionuclide generators
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Fission ProductionNuclei such as 99Mo, 131I, and 133 Xe are
produced in the fission products using an enriched 235U target (HEU – 90%)
Complex chemical processing (digestion or dissolution) and purification separates the 99Mo from chemically similar elements and radiocontaminents The result is a high specific activity (Bq/kg),
carrier free nuclide This means there is no stable isotope of the
element of interest Some negatives are the potential proliferation of
HEU targets and radioactive waste
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Neutron ActivationAn alternative use of reactors is to produce
radionuclides via neutron activation
Two drawbacks of this method are Small activation fraction Chemically similar carrier that cannot be
separated
IXenXe
PnPMonMo
XnX AX
AX
12553
12554
12454
3215
3115
9942
9842
1
,
, ,,
,
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Cyclotron ProductionCyclotron energies can be
a few MeV to a few GeV Laboratory/university or
hospital based Beam currents of 40-60 uA Produces Ci-level
radioisotopes
FnpO
OnpN
NpO
CpN
189
188
158
157
137
168
116
147
),(
),(
),(
),(
Siemens Eclipse
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Cyclotron ProductionThe reactions shown on the previous
page Are proton rich -> decay by e+ emission or EC
18F is the most common radionuclide in PET oncology
Are important elements of all biological processes hence make excellent tracers 18F is used to label FDG (18F-fluorodeoxyglucose) Useful because malignant tumors show a high
uptake of FDG because of their high glucose consumption compared with normal cells
Have short lifetimes (O(minutes)) Except t1/2 for 18F = 110 minutes
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Radionuclide GeneratorsGenerates a radionuclide by exploiting
transient equilibrium Most important application are moly
generators 99Mo (67 hours) decaying to 99mTc (6 hours)
Sodium pertechnetate (NaTcO4) results which can then be combined with an appropriate pharmaceutical
Developed at BNL, a particle and nuclear physics lab
Other generators also exist (69Ge to 68Ga, 82Sr to 82Rb, …)
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Radionuclide GeneratorsProcedure
A glass column is filled with aluminum oxide that serves as an adsorbent
Ammonia molybdenate attaches to the surface of the resin
A sterile saline (the eluant) solution is drawn through the column
The chloride ions exchange with the TcO4
- but not the MoO4-
The elute is thus Na+TcO4-
(sodium pertechnetate)
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Gamma CameraThese images are made using
gamma cameras We will cover the details of these (and
similar detectors) in upcoming lectures