1

Common Lab Sources

2

Radioactive Sources

3

Radionuclides in the AZ Particle Lab

Gamma60Co @ 1uC241Am, 133Ba, 137Cs, 60Co, 88Y, 22Na, 64Mg, 203Hg, 57Co @ 10 uC

X-ray55Fe

5.90 keV (24.4%) and 6.49 keV (2.86%)

Beta90Sr/90Y @ 50 mCi, 5 mCi, 2mCi, 0.5mCi

Alpha241Am @ 5 mCi

4

Radionuclides in MedicineNuclear medicine

Diagnostic Permits functional imaging (biochemistry and metabolism versus anatomical structure)>80% of all procedures use 99mTc

RadiotherapyTherapeutic

Primarily for cancer treatmentExternal beam – teletherapy using 60Co unitsInternal – brachytherapy using small, encapsulated sources

Notes90% of all radionuclide use in medicine is diagnosticUse of term “radioisotope” is commonWill there be a shortage of radionuclides in the future?

5

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

6

Radionuclides for Diagnosis

What are the characteristics of an ideal radionuclide for diagnosis?

Half-life?Effective half-life 1/τeff = 1/τradioactivity + 1/τbiological

Type and energy of radiation?Production and expense?Purity?Target area to non-target ratio?

7

Radionuclides for Diagnosis

The ideal gamma energy (for gamma camera use) is between 100 and 250 keV

8

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 functionSkeletal and bone marrow imagingPulmonary perfusionLiver and spleen functionCerebral perfusionMammographyVenous thrombosisTumor location

9

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

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

10

Technetium – 99mA closer look

There is no γ1emission, it IC’sIC competes with γ2

IC competes with γ3

X-ray and Auger electron emission can also occur

11

Radionuclides for TherapyBrachytherapy

Brachys = shortBrachytherapy uses encapsulated radioactive sources to deliver a high dose to tissues near the source

Provides localized delivery of doseBut the tumor must be well localized and small

Proposed by Pierre Curie and, independently, Alexander Graham Bell shortly after the discovery of radioactivityInverse square law determines most of the dosimetric effect

12

Brachytherapy

Used to treat a variety of cancers ProstateGynecologicalEyeSkin

Only ~10% of radiotherapy patients are treated via brachytherapy

13

BrachytherapySources

Most of the sources used emit gammasLower gamma energies are preferred for radioprotection

14

Brachytherapy

SourcesBut a few emit betas

90Sr/90Y for eye lesions90Sr/90Y , 90Y, 32P for preventing restenosis after angioplasty

In general, alphas and betas are absorbed by encapsulation to avoid tissue necrosis around the source

15

Nanotargeted Radionuclides

Use monoclonal antibodies to carry a radionuclide payload

16

BrachytherapySources

226Ra -> 222Rn + α -> … -> 206PbAlthough rarely used now, it’s a good reaction to know given its historical significance

17

BrachytherapySources

226Ra -> 222Rn + α -> … -> 206PbWhich equilibrium is achieved (t1/2(226Ra) = 1600 years)?222Rn is a radioactive gasAbout 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 MeVThe exposure rate constant (assuming 0.5 mm of Pt) is Γ = 8.25 R-cm2/hr-mCi

18

BrachytherapySources

More modern replacements for 226Ra are 137Cs

Familiar gamma ray spectrum with E=0.662 MeVt1/2=30 yrs and Γ=3.26 R-cm2/hr-mCi

and 192IrMore complicated gamma ray spectrum with <E> = 0.38 MeVt1/2=73.8 days and Γ=4.69 R-cm2/hr-mCi

19

Brachytherapy

Methods of deliveryLDR (0.4-2 Gy/hr) versus HDR (> 12 Gy/hr)Temporary versus permanentIntracavity versus interstitial

Also surface, intraluminal, intravascular, intraoperative

Seeds, needles, tubes, pellets, wire

20

Brachytherapy

21

Radionuclide Production

How are radionuclides made?Primary sources

Nuclear reactors235U fission produced Neutron activatedBoth produce neutron rich radionuclides

CyclotronsUses charged particle beams (p, d, t, α)Produces proton rich radionuclides

Secondary sourceRadionuclide generators

22

Nuclear Fission

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

23

Nuclear Reactors

Nuclear reactor schematic

24

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 interestSome negatives are the potential proliferation of HEU targets and radioactive waste

25

Neutron ActivationAn alternative use of reactors is to produce radionuclides via neutron activation

Two drawbacks of this method areSmall activation fractionChemically similar carrier that cannot be separated

( )( ) ( )( ) IXenXe

PnPMonMo

XnX AX

AX

12553

12554

12454

3215

3115

9942

9842

1

,

, ,,

,

→

+

γ

γγ

γ

26

Cyclotrons

We will cover accelerator physics later in the course

27

Cyclotron ProductionCyclotron energies can be a few MeV to a few GeV

Laboratory/university or hospital basedBeam currents of 40-60 uAProduces Ci-level radioisotopes

FnpO

OnpN

NpO

CpN

189

188

158

157

137

168

116

147

),(

),(

),(

),(

α

α

Siemens Eclipse

28

Cyclotron ProductionThe reactions shown on the previous page

Are proton rich -> decay by e+ emission or EC18F 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

29

Cyclotron Production18F in PET/CT

30

Cyclotron Production

Alzheimer’s diagnosis

31

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 pharmaceuticalDeveloped at BNL, a particle and nuclear physics labOther generators also exist (69Ge to 68Ga, 82Sr to 82Rb, …)

32

Radionuclide GeneratorsProcedure

A glass column is filled with aluminum oxide that serves as an adsorbentAmmonia molybdenate attaches to the surface of the resinA sterile saline (the eluant) solution is drawn through the columnThe chloride ions exchange with the TcO4

- but not the MoO4-

The elute is thus Na+TcO4- (sodium

pertechnetate)

33

Radionuclide Generators

Technetium cow

34

Radionuclide Generators

Generator schematic

35

Radionuclide Generators

Generally shipped weekly and milked daily

36

Gamma CameraThese images are made using gamma cameras

We will cover the details of these (and similar detectors) in upcoming lectures

37

Gamma CameraA schematic of a standard gamma camera