Common Lab Sources
1
Radioactive Sources
2
Radionuclides in the
AZ Particle Lab
 Gamma
Co @ 1uC
241Am, 133Ba, 137Cs,
57Co @ 10 uC
 60

60Co, 88Y, 22Na, 64Mg, 203Hg,
 X-ray
 55
Fe
 5.90 keV (24.4%) and 6.49 keV (2.86%)
 Beta

90Sr/90Y
@ 50 mCi, 5 mCi, 2mCi, 0.5mCi
 Alpha
 241
Am @ 5 mCi
3
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?
4
Radionuclides in Medicine
George 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
5
Radionuclides for Diagnosis
What are the characteristics of an ideal
radionuclide for diagnosis?

Half-life?
 Effective half-life 1/teff = 1/tradioactivity +
1/tbiological




Type and energy of radiation?
Production and expense?
Purity?
Target area to non-target ratio?
6
Radionuclides for Diagnosis
The ideal gamma energy (for gamma
camera use) is between 100 and 250
keV
7
Nuclear Medicine
 99mTc is used in ~ 80% of diagnostic
procedures
Tc pertechnetate (TcO4-) is mixed with an
appropriate pharmaceutical (biological construct)
for use for
 99m
 Cardiac imaging and function
 Skeletal and bone marrow imaging
 Pulmonary perfusion
 Liver and spleen function
 Cerebral perfusion
 Mammography
 Venous thrombosis
 Tumor location
8
Technetium – 99m
Half-life t1/2=6.02 hrs
Decay scheme

Which is (are) the medically useful
gamma(s)?
9
Technetium – 99m
A closer look




There is no g1
emission, it IC’s
IC competes
with g2
IC competes
with g3
X-ray and Auger
electron
emission can
also occur
10
Radionuclides for Therapy
 Brachytherapy


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
11
Brachytherapy
Used to treat a variety of cancers




Prostate
Gynecological
Eye
Skin
Only ~10% of radiotherapy patients are
treated via brachytherapy
12
Brachytherapy
Sources

Most of the sources used emit gammas
 Lower gamma energies are preferred for
radioprotection
13
Brachytherapy
Sources

But a few emit betas
 90Sr/90Y for eye lesions
 90Sr/90Y ,
90Y, 32P
angioplasty

for preventing restenosis after
In general, alphas and betas are absorbed
by encapsulation to avoid tissue necrosis
14
around the source
Nanotargeted Radionuclides
Use monoclonal antibodies to carry a
radionuclide payload
15
Brachytherapy
Sources

226Ra
->
222Rn
+ a -> … ->
206Pb
 Although rarely used now, it’s a good reaction
to know given its historical significance
16
Brachytherapy
Sources

226Ra
->
222Rn
+ a -> … ->
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 G = 8.25 R-cm2/hr-mCi
17
Brachytherapy
Sources

More modern replacements for
137Cs
226Ra
are
 Familiar gamma ray spectrum with E=0.662
MeV
 t1/2=30 yrs and G=3.26 R-cm2/hr-mCi

and
192Ir
 More complicated gamma ray spectrum with
<E> = 0.38 MeV
 t1/2=73.8 days and G=4.69 R-cm2/hr-mCi
18
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
19
Brachytherapy
20
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, a)
Produces proton rich radionuclides
Secondary source
 Radionuclide generators
21
Nuclear Fission
Fission of 236U* yields two fission nuclei
plus several fast neutrons
22
Nuclear Reactors
Nuclear reactor schematic
23
Fission Production
 Nuclei 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
24
Neutron Activation
 An alternative use of reactors is to produce
radionuclides via neutron activation
A
X
98
42
X n, g 
A1
X
X
Mon, g  Mo, Pn, g  P
124
54
99
42
31
15
Xen, g  Xe I
125
54
32
15
125
53
 Two drawbacks of this method are


Small activation fraction
Chemically similar carrier that cannot be separated
25
Cyclotrons
We will cover accelerator physics later
in the course
26
Cyclotron Production
 Cyclotron 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
14
7
N ( p, a ) C
16
8
O( p, a )137N
15
7
N ( p, n)158O
18
8
Siemens Eclipse
11
6
18
9
O ( p, n) F
27
Cyclotron Production
The 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
28
Cyclotron Production
18F in PET/CT
29
Cyclotron Production
Alzheimer’s diagnosis
30
Radionuclide Generators
 Generates 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, …)
31
Radionuclide Generators
 Procedure





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 MoO4The elute is thus Na+TcO4- (sodium
pertechnetate)
32
Radionuclide Generators
Technetium cow
33
Radionuclide Generators
Generator schematic
34
Radionuclide Generators
Generally shipped weekly and milked
daily
35
Gamma Camera
These images are made using gamma
cameras

We will cover the details of these (and
similar detectors) in upcoming lectures
36
Gamma Camera
A schematic of a standard gamma
camera
37