1

Common Lab Sources

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Radioactive Sources

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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 – 99mHalf-life t1/2=6.02 hrsDecay scheme

Which is (are) the medically useful gamma(s)?

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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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Nanotargeted Radionuclides

Use monoclonal antibodies to carry a radionuclide payload

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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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Brachytherapy

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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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Nuclear Fission

Fission of 236U* yields two fission nuclei plus several fast neutrons

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Nuclear Reactors

Nuclear reactor schematic

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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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Cyclotrons

We will cover accelerator physics later in the course

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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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Cyclotron Production

18F in PET/CT

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Cyclotron Production

Alzheimer’s diagnosis

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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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Radionuclide Generators

Technetium cow

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Radionuclide Generators

Generator schematic

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Radionuclide Generators

Generally shipped weekly and milked daily

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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

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Gamma CameraA schematic of a standard gamma

camera