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Chapter 3: Production of Short Half-Life PET Radionuclides 69
Chapter 4
Production of
Radionuclides
Used in SPECT
Salma Jivan1 and Thomas J. Ruth
1
Biomedical Isotope Facility, Berkeley Lab, Helen Wills
Neuroscience Institute, University of California, Berkeley,
Berkeley, CA 94720, USA
2
Life Sciences Division, TRIUMF and BC Cancer Research Centre,
Vancouver, BC V6T 2A3, Canada
2
4.1 INTRODUCTION
This chapter describes the production and isolation methods for obtaining the radionuclides used in single photon emission computed tomography (SPECT). The radionuclides
used in SPECT are produced in reactors or from proton bombardment of targets at cyclo-
tron facilities. Table4.1 lists the radionuclides used in the majority of procedures. The
table also includes the half-life, major decay mode, as well as decay product for each of
these radionuclides.
The following sections present the radionuclide with a description of how it is pro-
duced along with typical separation/purication approaches presently used. However, it
should be noted that since these radionuclides are produced commercially, the exact pro-
cedures used by the various manufacturers are proprietary and thus may not reect what
is used by each producer.
Handbook of Radiopharmaceuticals: Methodology and Applications, Second Edition.
Edited by Michael R. Kilbourn and Peter J.H. Scott.
© 2021 John Wiley & Sons Ltd. Published 2021 by John Wiley & Sons Ltd.
Table 4.1 Table
ofSPECT
radionuclides.
Isotope Half-life Primary decay (keV) Decay product
99m
Tc 6 h 140
131
I 8 d 364, 637
201
Tl 7 2 h 70–80 (X-rays)
67
Ga 78 h 93, 185
111
In 67 h 245, 172
123
I 13 h 159
133
Xe 5 d 81
Source: Based on NRC (National Research Council). 2007. Advancing Nuclear Medicine Through Inno-
vation. Washington, DC: The National Academies Press. Available at https://doi.org/10.17226/11985.
99
Tc (2.1 × 105 yr)
131
Xe (stable)
201
Hg (stable)
67
Zn (stable)
111
Cd (stable)
123
Te (9.2 × 1016 yr)
133
Cs (stable)
4.2 TECHNETIUM-99m
SPECT imaging is dominated by
dures. Historically,
ssion products of
99
of the
Mo/
99m
Tc is derived from a 99Mo generator, which is extracted from the
235
U. The year 2018 marked the 60th anniversary of the development
99m
Tc generator at Brookhaven National Laboratory in New York (https://
www.bnl.gov/newsroom/news.php?a=213162).
The development of this generator opened the eld of nuclear medicine to a simple
source of radioactivity that could be supplied internationally. The 66-hour half-life of
99
Mo allowed for remote producers to produce the isotope and prepare a generator to
be shipped to hospitals or central pharmacies. Over the next several decades, chemists developed tracers that can be used in the diagnoses of various disease conditions.
Table4.2 provides some examples of the use of
The thermal neutron ssion of
Figure4.1 illustrates the ssion yield curve for various isotopes as a function of atomic
mass. Note that the yield in Figure4.1 shows that the two maxima are for atomic masses
at A=100 and 130.
As can be seen from the curve, the isotopes of interest to medicine (
produced in large abundance (3–5% of each ssion). For several decades, highly enriched
235
U (HEU; >93%) was the target of choice because the uranium targets could be made in the
form of pellets or compact plates for ease of dissolution. Such targets occupied a relatively
small space in a reactor’s core due to the high density of uranium and high enrichment.
More recently, there has been a push from the nuclear safeguards community for
removal of highly enriched ssile material from civilian use because a relatively small
quantity of enriched
235
U could be used to produce a nuclear bomb. As part of this eort,
a study performed by the US National Academy of Sciences indicated that conversion
from HEU to low enriched
within a reasonable cost structure[2]. At the time of this writing (2018), several of the
international producers have converted from HEU to LEU targets, and new facilities have
been designed from the start to use LEU[3]. The conversion has been challenging and
costly, resulting in some disruption of supply.
99m
Tc, which accounts for more than 80% of all proce-
235
U provides the most ecient source of 99Mo.
235
U (LEU; dened as <20%
99m
Tc.
99m
131
Tc,
235
U) could be technically achieved
133
I,
Xe) are
72 Handbook of Radiopharmaceuticals
99m
10
Atomic Mass Number
Fission Yield (%)
0
Tc radiopharmaceutical Primary use
Sestamibi (Cardiolite) Myocardial perfusion imaging
Tetrofosmin (Myoview) Myocardial perfusion imaging
Medronate (methylene diphos-
Bone imaging
phonate, MDP)
Tc-99m oxidronate (TechneScan;
Bone imaging
hydroxydiphosphonate, HDP)
Pyrophosphate Avid infarct imaging
Mebrofenin (Choletec) Hepatobiliary imaging
Mertiatide (MAG-3) Renal imaging
Gluceptate Renal imaging
Tc-99m pentatate (diethylene
Renal imaging and function studies
triamine pentaacetic acid, DTPA)
Pertechnetate Imaging thyroid, salivary glands, ectopic gastric mucosa,
parathyroid glands, dacryocystography, cystography
Macroaggregated albumin (MAA) Pulmonary perfusion
Exametazime, HMPAO (Ceretec) Cerebral perfusion imaging
Bicisate, ethyl cysteinate dimer
Cerebral perfusion imaging
(ECD) (Neurolite)
Source: Based on NRC (National Research Council). 2007. Advancing Nuclear Medicine Through Innovation.
Washington, DC: The National Academies Press. Available at https://doi.org/10.17226/11985.
Table 4.2
Exam-
ples of radiopharmaceuticals
labelled with
99m
along with their
primary usage.
Tc
1
0.1
0.01
0.001
60 80 10 0120
140160 18
Figure 4.1 Fission
yield for thermal
neutron ssion of
235
U. Source: Data
from Handbook
of Nuclear Data
for Safeguards:
Database Extensions, August
2008. Prepared
by A.L.
Nichols,
D.L. Aldama, and
M. Verpelli. INDC
International
Nuclear Data
Committee.
International
Atomic Energy
Agency 2008.
Retrieved from:
https://www-
nds.iaea.org/
sgnucdat/c1.htm.
Chapter 4: Production of Radionuclides Used in SPECT 73
However, a larger disruption in the 2008–2009 period, with the two largest producers
lasting more than one year, caused great concern for the nuclear medicine community[4].
Subsequently, several initiatives began to explore alternative routes to
99m
Tc[5]. These included building new reactors or repurposing existing reactors as well as
99
Mo and/or
developing new technologies to produce these radionuclides. Again, as of this writing,
only two new approaches have demonstrated the ability to produce useful quantities.
NorthStar Medical Technologies, LLC has made use of an old technology,
produce low-specic-activity
99
Mo. However, this product is not compatible with existing
generator systems because of the large mass of Mo in the product (
98
Mo(n,γ)99Mo, to
98
Mo and 99Mo). Thus,
a new generator approach had to be built. Such a new generator system (Radiogenix) was
designed to supply
99m
Tc of suciently high concentration to be compatible with exist-
ing pharmaceutical kits to be used in the clinic (https://www.northstarnm.com/products/
northstar-solutions-radiogenix-system). It is too early to determine how successful this
99
approach will be in supplementing the supply of
Mo/
99m
Tc.
The other approach developed by two Canadian consortia makes use of small medical cyclotrons (16–24 MeV protons) to produce
99m
Tc directly via the
100
Mo(p,2n) reac-
tion[6,7]. While this approach has been demonstrated to produce sucient quantities
for regional distribution, it has not been adopted for clinical use as of this writing.
It is beyond the scope of this chapter to provide a more in-depth discussion of this
aspect of
99m
Tc availability.
4.3 IODINE-131
131
While
more ecient to produce via the
for a neutron source[5]. I-131 decays by beta emission and has two primary gamma rays
at 364 and 637 keV.
However, with an eight-day half-life and relatively high photon energies, an alternative
iodine isotope was sought. The best candidate was
With the introduction of
be seen from Figure4.2,
I is a ssion product that can be extracted during the processing for 99Mo, it is
For many years,
130
Te(n,γ) →
131
I–radiopharmaceuticals were used in diagnosing various diseases.
123
I radiopharmaceuticals, the use of
131
I is used primarily for therapeutic purposes.
131
I reaction. In either case, there is a need
123
I (discussed in a later section)[8].
131
I has diminished. As can
4.4 XENON-133
Xenon-133 (5d; photon at 81 keV) is also a
released upon the dissolution of the uranium target. Thus, the
in the gas stream during dissolution. The demand for
Other jurisdictions use
74 Handbook of Radiopharmaceuticals
235
U ssion product. As a noble gas, it is
133
99m
Tc tracers for ventilation studies[5].
133
Xe needs to be trapped
Xe is primarily in North America.