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Radionuclides in Medicine and Research212
Table 1: Radionuclides for Diagnostic Radiopharmaceuticals in Clinical Nuclear Medicine and Medical
Research
(I) Gamma Emitters
Radionuclide T
Decay mode Main E keV(%) Method of Production
1/2
(i) ‘Versatile’ Tracers
99m
Tc 6h IT 140.5 (89)
111
In 2.8d EC 171 (90) Cd (p, xn);
245 (94)
123
I 13.3h EC 159 (83)
(ii) Tracers of ‘Specific’ Utility
67
Ga 78h EC 93 (37) Zn (p,xn);
185 (20)
131
I 8d
-
364 (81);
637 (7)
201
TI 73h EC 69-80(95)
Hg X-rays
135(3) & 167(11)
(II) Positron (+) Emitters for PET
99
99m
Mo-
Tc Gen.
109
Ag (,2n)
124
Xe (p,2n)
123
’
123
Te (p,n);
65
Cu (, 2n)
130
Te (n,);
235
U (n,f)
203
TI (p,3n)
123
Cs(5.9 m; +/EC)
Xe(2.08 h; +/EC)’;
124
Te (p,2n)
131
Te(25 m; –)’;
131
I
201
Pb(9.33 h; +/EC)’
Radionuclide T
11
C 20.4 m 0.96 200
13
N 10 m 1.19 200
15
O 2 m 1.72 200
18
F 110 m 0.635 194
64
Cu 12.7 h 0.656 38.6
68
Ga 68 m 1.899 178
75
Br 96.7 m 1.721 151
82
Rb 1.3 m 3.4 192
86
Y 14.7 h 3.141 68
124
I 4.18 d 2.138 50
1/2
E+ MeV 511 keV rays % Method of production
14
N (p,)
16
O (p,)
14
N (d,n);16O (p,pn)
18
O (p,n); 20Ne (d,)
64
Ni(p,n);
69
Ge(p,2n);
65
Cu(p,pn)
nat
Ge(p,xn); 68Ge 68Ge (288
d; EC)68Ga gen.
76
Se(p,2n)75Br
82
Sr (25.55 d; EC)82Rb Gen.
Zr, Mo (p, Spallation)82Sr
88
Sr(p,3n)86Y
124
Te(p,n);
125
Te(p,2n)
Radionuclides in Medicine and Research 213
Table 2: Important Radionuclides for Therapy
(a) Alpha emitters
RN T
211
At 7.2h 6.76
212
Bi 60.5 min 7.8
213
Bi 45.6 min 5.87
255
Fm 20.1h 7
1/2
E (mean), MeV Method of Production
209
224
212
225
225
255
(b) ‘Pure’ beta emitters
RN T
32
P 14.3d 1.71
33
P 25.3d 0.25
89
Sr@ 50.5d 1.46
90
Y 2.67d 2.27 –Decay of 90Sr (28.3y); 90Sr-90Y gen.
143
Pr 13.6d 1
1/2
E- (mean), MeV Method of Production, % nat. abun.;
32
S (n,p); 95; (n,p) = 0.53 b
33
S (n,p); 0.75; (n,p) = 0.002 b
88
Sr (n,); 82.6; 0.0058 b
89
Y (n,); 100; 1.3 b
142
(c) Beta emitters with ‘low abundance’ gamma emission
RN T
1/2
E- (max.), E/keV (%) Method of production, % nat. abun.;
MeV
105
Rh 35.5h 0.57 319 (19)
104
306 (5)
153
Sm 46.3h 0.81 103 (28)
166
Ho 1.1d 1.85 81 (6.33)
175
Yb 4.18 d 0.48 282(3.1)
152
165
174
396(6.5)
177
Lu 6.7d 0.49 113 (6.4)
176
208 (11)
186
Re 3.7d 1.07 137 (9)
188
Re 17h 2.11 155 (15)
185
187
188
186
Bi (, 2n)
213
212
Pb
Bi
Ra(3.63d)3 successive s
Pb(10.6 h; –) -
212
Bi gen
Ac(10d) 3 successive s
213
Ac-
Bi gen
Es (39.8 d; –)
143
Ce(n,)
Ru (n,)
255
Fm
Ce(33 h; –); 11; 0.95 b
105
Ru(4.44h; –)18.7; 0.5 b
Sm (n,); 26.7; 206 b
Ho (n,); 100; 58 b
Yb (n, ); 31.6; 69 b
Lu (n,); 2.6; 2100 b
Re (n,); 37.4; 106 b
Re (n,); 62.6; 73.2 b; - Decay of
188
W-
Re gen.
W (n,)
187
W(n,)
188
W; 28.6; 37.8 b; 70 b
188
W(69.4d);
(d) Beta emitters with ‘high abundance’ gamma emission
Radionuclides in Medicine and Research214
RN T
1/2
E- (max.), E/keV (%) Method of production, % nat. abun.;
MeV
47
Sc 3.35d 0.6 160 (73) Spallation reaction on Ni
67
Cu 62h 0.57 184 (49)
68
Zn(p,2p); 19
92 (16) Spallation reaction on As
131
I 8d 0.6 364 (81)
130
235
131
Te(n,)
Te(25 m; –); 33.8;0.23 b
U (n,f); ~6% fission yield; 540b
(e) Auger E- and other particulate emitters
RN T
1/2
Decay characteristics Method of Production % nat. abun.;
and major energy, keV
103
Pd 17d EC; IC e- 16, 36, 39; E/X 20
103m
Rh 56.1 min IT; IC e-; E 40
117m
Sn 13.6 d IT; IC e- 130, 160, E 159
124
I 4.15d +, EC; Auger e-;E 603
125
I 60d EC; IC & Auger e-; E 35
169
Er @ 9.4d - ;IC e- 340;
@ Gamma emission of 909 keV of 89Sr and 110 keV of
103
Rh (p,n); 100;
102
Ru (n,)
103
Ru/
116
Sn (n,); 14.7; 0.006 b
124
Te (p,n); 4.82;
125
Te (p, 2n); 7.14;
124
Xe(n,)
168
Er (n,); 26.8; 2 b
169
Er of very low abundance has been ignored in this
103m
103
Rh gen;
125
classification.
Ru(39.3 d; –); 31.6;1.2 b
Xe(16.9 h; EC); 0.1;110b
Table 3: Important radionuclides for therapy in terms of the nature of particulate emission
Particulate emission Examples
Beta emitters
(Range: 1-12 mm)
Hard betas (E max over 1.5 MeV)
Medium betas (E max 0.5-1.5 MeV)
Soft betas (E max less than 0.5 MeV)
‘Pure’ beta emitters
Beta emitters with ‘minor’ gamma emission
32
131
33
32/33
153
188
P, 90Y,
153
I,
Sm,
169
P,
Er,
P, 89Sr, 90Y,
166
Sm,
Ho,
Re,
186
177
166
Re, 89Sr
Lu
143
177
Lu,
Ho
Pr,
186
169
Re,
Er
188
Alpha emitters
211
212
213
(40-80 m range for E = 5-8 MeV)
At,
Bi,
Bi,
256
Fm
Auger electrons/Conversion electrons emitters
124
125
(Range : nm to m)
I,
I,
117m
Sn
Re
Radionuclides in Medicine and Research 215
Early generation radionuclides
131
I, 32P and 51Cr belonging to this group continue to be of relevance, while the others such as
24
Na, 32P, 82Br,
for therapy of thyrotoxicosis and differentiated thyroid cancer. The neutron irradiation of tellurium
targets remains the method of choice for production of
235
of
U is also done in facilities dealing with large scale production of fission-produced 99Mo.
Dry distillation of iodine has become the preferred method for radiochemical separation from
irradiated tellurium. This has been mainly due to reduced quantity of waste generation and
increased chemical purity of
systems are available for deploying in shielded plants/hot cells.
Molybdenum-99
99
Mo, the parent nuclide of
classified under early generation radionuclides. There have been considerable efforts over the
years to improve upon the production capacity as well as technology for 99Mo (apart from the
generator systems for
column chromatography generators.
In order to sustain over 20 million studies annually performed using
importance to assure access to appropriate technologies for continued, reliable availability of
99m
Tc generators and in turn, that of the raw material radionuclide 99Mo estimated to be of the
order of 10000 to 12000 Ci per week at reference time (usually 6 days after the end of reactor
irradiation) and throughout the year (4).
The parent radionuclide 99Mo for
targets in a nuclear reactor with a fission yield of about 6.1%. There are only a limited number of
production centers of fission product 99Mo. Currently well over 95% of the fission product 99Mo
is obtained using highly enriched uranium (HEU) targets. The Nuclear Energy Commission of
Argentina (CNEA) produces 99Mo using low enriched uranium (LEU) plate targets (<20%
while the Australian Nuclear Science and Technology Organisation (ANSTO), will be using
LEU plate targets for larger quantities of fission 99Mo production in the new research reactor
called OPAL.
198
Au etc have lost regular clinical utility.
131
I obtainable by this procedure. Safe, reliable, automated processing
99m
Tc, the most important in vivo diagnostic tracer, can also be
99m
Tc (3,4). The fission route is essential in order to have user-friendly
99m
Tc generators is mostly prepared by the fission of
131
I continues to occupy a vital position
131
I, while isolation from fission products
99m
Tc, it is of utmost
235
235
U
U),
There are two main methods of production of fission 99Mo; one involving acidic dissolution
of the targets, while the other originating from Karlsruhe group, involves alkaline digestion of
the targets. Two publications of the IAEA are notable, one on fission produced 99Mo released in
1989 based on a meeting held in Germany and the other subsequently in 1998 following a
meeting held in South Africa; the latter is a review of the field including a look at the alternate
routes covering accelerator based methods (including accelerator driven systems (ADS) route)
for the production of 99Mo, as well as at the technologies of
pure 99Mo from the fission products of
235
U is a very complex process and industrial/corporate
99m
Tc generators. The separation of
efforts have been far more dominant in this area. It is a capital intensive technology and practice
and hence volume/scale of operation is another crucial factor. This is the main reason for most
Radionuclides in Medicine and Research216
countries to follow the soft option of purchasing commercially available fission 99Mo in bulk for
99m
Tc generator production. It is however necessary that major production centers of fission
99
Mo are well spread throughout the world, in order to render better transport logistics and
economy in freight costs.
Technetium-99m
99m
Tc holds the pivotal position in diagnostic nuclear medicine due to its versatility for imaging
the skeletal, renal, hepatobiliary, pulmonary system, in addition to tracing the blood flow to vital
organs like brain and myocardium, by virtue of its facile complexation with a variety of specific
molecules and ligands. The assured commercial availability of fission product 99Mo, a product of
a high technology process, has led to local production of the user friendly alumina column
chromatography generators in several countries including in the developing nations. There is a
choice of proven technology for adaptation, wet generators versus dry generators and aseptic
charging of 99Mo on pre-sterilized alumina columns versus steam sterilization of loaded alumina
columns, with well-known merits and demerits of each option. Alternate technology using solvent
(methylethylketone, MEK) extraction of
producible with relatively much more ease and at low cost by neutron activation of molybdenum
trioxide targets in nuclear reactors [called (n,)99Mo], has been adopted in many other places;
mostly units are operated at a centralized or national radiopharmacy and the separated
distributed to medical users. In India, the unique status of hospital based individual solvent
extraction units has been in vogue for over 35 years now, thanks to the early bold approaches of
the radiopharmacists of Department of Atomic Energy (DAE) and willing user physicians, under
the watchful eyes of the hospital pharmacists and medical physicists. Due to stringent
pharmaceutical regulatory needs, the concept of commercially run licensed radiopharmacies
distributing ready-to-use
99m
Tc formulations, to the extent of individual doses specific for each
patient, is being followed in a number of countries around the world.
99m
Tc from 99Mo of low to medium specific activity,
99m
Tc is
Based on the initial efforts of scientists from Australia, another approach called gel generator
99m
for
Tc has been adopted by a number of countries interested to make use of (n,)99Mo for
column
99m
Tc generators. In this method, one tries to combine the advantages of the ease,
simplicity and reliability of a column type generator with easy to produce inexpensive (n,)99Mo
of medium specific activity of 15-37 GBq/g (0.4-1 Ci/g). However, the processing is quite
complex due to several factors influencing the gel characteristics and in turn its final performance.
The processing of the 99Mo gel is not manufacturer-friendly and hence the early promise of gel
system was not realizable for a long time. The developments in automated modules for
radiochemical processing and better understanding of the gel manufacture process are driving a
re-look at this technology option for interested countries having research reactors (RR) with
suitable features such as adequate neutron flux and number of irradiation positions and regular
weekly operational schedules.
An important beginning has been made in India in this regard at the Board of Radiation and
Isotope Technology (BRIT) (5). An assembly line consisting of a series of four shielded units has
been set up for medium scale production of zirconium molybdate 99Mo gel and the generators
are now being supplied on regular basis every fortnight, to some users who need
99m
Tc in
Radionuclides in Medicine and Research 217
moderate amounts. Similar successful results have been achieved by China too and it is believed
that regular supply of zirconium molybdate based gel generators were made by the Chinese
laboratory some years ago. A few other countries are also aspiring to follow this route to be
indigenously self sufficient in production of
99m
Tc.
An independent development coming from Oak Ridge National Laboratory (ORNL), USA,
(6) involving concentration of perrhenate and pertechnetate eluates by passage through a tandem
cation–anion exchanger column system will strengthen the possibility to prepare larger bed
alumina column generators to hold 99Mo of medium specific activity of 37-74 GBq/g (1-2 Ci/g)
and yet obtain
99m
Tc of acceptable radioactive concentration for regular medical use. The utility
of this strategy is especially significant in the context of a large/centralised radiopharmacy, as
well as in nations with reactor capability for production of (n,)99Mo of such specific activity.
Development of alternate adsorbent materials (to replace alumina) capable of taking up
much larger quantities of molybdenum was another strategy to prepare column based generators
using the (n,)99Mo. The Japanese work on an inorganic polymeric compound called poly
zirconium compound (PZC) has been in the reports for some years and more recently pursued as
a project under the FNCA scheme (Forum for Nuclear Cooperation in Asia; web link: www.fnca.jp/
english/newsletter/fnca_news_no10.pdf).
Other reactor based radionuclides
125
I finds extensive use as the ideal radiolabel for antigens and antibodies in immunoassays, apart
from its use as sealed sources for intra-ocular and prostate cancer therapy and some industrial
applications.
for production of
system for use with enriched
avoidance of the
125
I is a good candidate for internalized cytotoxicity too (Table 2). The technology
125
I has matured to the point of commercial availability of the loop irradiation
126
I impurity are thus achieved.
124
Xe targets. Reliable re-use of the expensive target as well as
There has been revival of interest in the radionuclide 32P. Its relatively longer half-life of
14.3 days and ease of production have contributed to its widespread availability. This radionuclide
finds increased application in biotechnology and molecular biology e.g. as 32P labelled nucleotides,
as well as in radionuclide therapy (RNT). There are many other reactor based radionuclides
useful for RNT and are covered later in this Chapter.
Cyclotron based radionuclides - Gamma emitters
The cyclotron produced
myocardial perfusion imaging and imaging of many lesions (soft tissue tumors, abscesses),
respectively, despite the well-known drawbacks in their nuclear and biological properties (Table
111
1).
In has been an adjuvant to
negative ion acceleration, leading to a much higher extracted beam current (350-500A), mastered
by a Belgian Company (IBA, Belgium) (7), is widely deployed for industrial scale production of
many radionuclides (e.g. model Cyclone-30). The choice of 30 MeV protons is dictated by the
production parameters needed for the most important product, namely,
The early attempts to harness the merits of
201
Tl and 67Ga have continued to play their useful clinical role in
99m
Tc, for studies requiring delayed imaging. The technology of
201
TI (Table 1) (8).
123
I as diagnostic tracer were hampered by the
Radionuclides in Medicine and Research218
unacceptable levels of
124
I contaminant, apart from logistic problems of distribution due to its
limited shelf life. Development of appropriate technology in terms of production through precursors
123
of
I viz.
utilization of this ideal tracer (8). The commercial availability of high purity
123
123
Xe/
Cs, use of highly enriched gas target of
124
Xe etc. have helped practical
123
I despite its high
cost, has revived the interest in radioiodinated products for imaging tumors, mapping receptors
and studies in blood flow to brain and myocardium. The
123
I production technology described
above is very expensive due to both the price for the technology as well as the very highly
enriched target of
124
Xe. For reasons of economy, alternate means of accessing to
lower shelf-life) would merit attention e.g.
123/124
Te target route (Table 1) (8).
123
I (of even
Using the Variable Energy Cyclotron (VEC) facility of DAE at Kolkata, limited quantities of
67
Ga have been made since 1991 at the Radiopharmaceutical Laboratory of BRIT located at VEC
Centre (VECC), Kolkata and utilized mainly at Regional Radiation Medicine Centre, VECC,
Calcutta. Feasibility of production of clinically useful quantities of
demonstrated. Currently,
201
Tl is being imported by many users in India and about 70-110 GBq
111
In has also been
is used every week. A 30 MeV cyclotron with capacity to have four beam lines is expected to be
commissioned soon at Kolkata, India. This would be a multi-purpose machine operated by both
BRIT and VECC and a significant number of important medical isotopes such as 64Cu, 67Ga,
103
111
123
Pd,
In,
201
I,
Tl, are expected to be available in future.
Among the cyclotron-based radionuclides used in medicine, the recent emergence of
Palladium-103 (
103
Pd, T1/2=17d, EC decay mode, E=40 keV) for brachytherapy of prostate
cancer and the consequent design and development of a high current, medium energy (2-3 mA,
18 MeV proton) cyclotron called “palladium making cyclotron” (also of IBA, Belgium) deserve
a special mention. A discussion on radionuclides for brachytherapy is beyond the scope of the
present article. The considerable potential of radionuclide therapy (RNT) and products for RNT
are described later in this Chapter.
Cyclotron based radionuclides - Positron emitters
Radioisotope production for Positron Emission Tomography (PET) is currently accomplished
using cyclotrons producing 11 to 18 MeV protons. The major group of positron emitter tracers of
biological elements, viz., 11C, 13N, 15O and their analog 18F, are important for PET studies of in
vivo biochemistry (Table 1) (8). In view of considerable advances in 18F based
radiopharmaceuticals, mainly 2-fluoro-2-deoxyglucose (FDG), ‘18F-FDG - PET pair’ has become
analogous to ‘
A medical cyclotron facility can normally cater to the requirements of more than one
PET centre, typically 4 or 5 PET centres in the vicinity. The largest growth in production and
clinical utilisation has been in 18F-based products, with 2.5 million PET studies estimated in
2005 amounting to 10% of all nuclear medical imaging procedures done that year. Protons
bombarding water targets enriched with 18O produce 18F of 110 minutes half-life and requires
rapid production and distribution cycles and adequate target inventories. The R&D efforts in the
past few years focused on maximizing the beam power deposited per unit target mass while
maintaining pressures and temperatures at levels acceptable to conventional beam window materials
and led to automated, reliable large-scale production technologies. Daily large-scale production
99m
Tc - SPECT pair’ in clinical nuclear medicine.
Radionuclides in Medicine and Research 219
of 18F followed by rapid synthesis of 18FDG [batch sizes as large as 185 GBq (5 Ci) of 18F and
74-111 GBq (2-3 Ci) of 18FDG] for distribution over a few hundred kilometres and involving up
to several hours of road travel are routine activities in many countries now. Multiple runs of 18F
production as well as use of large volume water targetry for 18F production are feasible to cater
to the increasing demands for clinical and research applications. Recycling of the enriched water
for several runs is quite common, while a patented method of recovery along with equipment is
also available from the Institute of Nuclear Chemistry, Research Centre of Juelich, Germany.
The installation of a medical cyclotron - PET system in 2002 by Department of Atomic
Energy (DAE) at Tata Memorial Centre (TMC), Parel, Mumbai was an important milestone in
the growth of nuclear medicine in India. Currently there are 7 medical cyclotrons in operation in
India with over 12 PET and/or PET-CT units in regular service.
The spare time of many medical cyclotrons available is tapped to produce other non-standard
PET tracers such as 64Cu (12.7 h) and
124
I (4.18 d), which have shown promise for few applications.
They need ~12 MeV protons for their production which can be feasible with most of the medical
cyclotrons (8). However, use of highly enriched targets is necessary, for production of these
radionuclides. There are several other radionuclides of similar interest.
In view of the huge growth in the number of PET centres all over the world, there is also an
increasing interest to use generator-produced positron emitters (Table 4), in particular, 68Ga (68.3
min) available from 68Ge-68Ga generator. The merits of PET imaging and ease of PET accessibility
have triggered a re-look at the prospect of regular use of 68Ga radiopharmaceuticals. The progress
in chemistry of separation of gallium as well as preparation of lesion specific tracers is an
additional factor helping the revival of interest in development and use of 68Ga-based products. A
TiO2-based generator is commercially available, but the large-scale production of 68Ge is currently
almost a monopoly of a company in Russian Federation.
The potential of radionuclides of copper for both diagnosis and therapy has also driven an
interest in 62Cu (9.67 min) available from a 62Zn-62Cu generator (based on ion exchange
chromatography over Dowex-1 or CG-120 Amberlite), although the short half-life of 62Zn (9.2 h)
precludes wider exploration. 82Rb (1.3 min) availed from 82Sr-82Rb generator is useful for PET
imaging of myocardial perfusion. The parent nuclide 82Sr (25.5 d) can be produced in high
energy cyclotrons, by spallation of Mo/Nb targets with >200 MeV protons or by Rb(p,xn)
reaction with 70 MeV protons (Table 4).
Table 4: Generator-Produced PET Radionuclides
Part I: Systems in use or under development
Daughter T
nuclide Positron nuclide production energy, MeV
62
Cu 9.7 min 98
68
Ga 68.3 min 90
82
Rb 1.3 min 96
1/2
Daughter Parent T
yield (%) method
62
Zn 9.2 h
68
Ge 271 d
82
Sr 25.5 d Rb(p,xn) 70 50
1/2
Common Projectile
63
Cu(p,2n) 25 15
69
Ga(p,2n) 25 15
As/Br/Rb(p,spall) >200
Mo/Nb(p,spall) >200
Part II: Products of potential interest
Radionuclides in Medicine and Research220
Daughter T
1/2
Daughter Parent T
1/2
nuclide Positron yield (%) nuclide
52m
Mn 21.1 min 98
122
I 3.6 min 77
118
Sb 3.6 min 83
128
Cs 3.6 min 61
44
Sc 3.9 h 95
72
As 26 h 77
52
Fe 8.27 h
122
Xe 20.1 h
118
Te 6.0 d
128
Ba 2.43 d
44
Ti 47 y
72
Se 8.4 d
Radionuclides of biological elements emitting positrons have enabled not only the tracing of
biochemical pathways in vivo using PET in nuclear medicine, but also led to reliable screening
of candidate molecules for drug development through sophisticated metabolic studies in animal
models. The use of 11C and 18F labelled compounds in conjunction with small animal PET units
has proved a powerful tool in such investigations for drug development. The value of such
studies to pharmaceutical industries is immense on account of the enormous savings from
evidence-based objective screening to restrict the number of molecules to be taken further for
development, as well as to decide on dropping out the unsatisfactory ones.
The emerging need for some PET tracers, such as 86Y,
94m
Tc (Table 5) for reliable internal
dosimetry calculations, is covered at the end of the next section.
Table 5 : Surrogate Radionuclides for Dosimetry Estimates for Therapy
Therapy T
RN for imaging emitter/ RN E/keV (%) + emitter
E/keV (%) Surrogate T
1/2
SPECT PET
1/2
Surrogate Surrogate T
1/2
67
Cu 2.58 d 91.27(7) Self
93.31(16.1)
62
Cu 9.74 m
64
Cu 12.7 h
188.58(48.7)
89
Sr 50.5d —
90
Y 2.7d —
85
Sr 64.9d 514 — —
87m
Sr 2.8h 388
111
In 2.8d 171 (90)
86
Y 14.7h
245 (94)
125
I 60d —
131
I 8d 364 (81) Self/
153
Sm 1.9d 103 (28) Self/
123
I 13.3h 159 (83)
123
I 13.3h 159 (83)
99m
Tc 6h 140.5 (89)
124
I 4.15d
124
I 4.15d
94m
Tc 52 min
(EDTMP) (MDP) (MDP)
186
Re 3.7d 137 (9) Self/
188
Re 17 h 155 (15)
99m
Tc 6h 140.5 (89)
94m
Tc 52 min
Radionuclides in Medicine and Research 221
Radionuclides for therapy
Radionuclides have provided extra ammunition to the physicians to combat some diseases since
early times. The efficacious treatment of thyroid disorders, one benign (thyrotoxicosis) and
another malignant (thyroid cancer), with radioiodine,
over. There are several large centres in India offering the radioiodine treatment services e.g.
Radiation Medicine Centre (RMC), BARC, Mumbai; AIIMS, New Delhi, just to cite a few.
The therapeutic radionuclides could be classified on the basis of their half-lives as well as on
the type of particulate emissions (Table 2 and 3). The large variety of nuclides with varied
energies of the emitted particles, and hence penetration in tissues, offer a choice to select the
isotope depending on the volume of lesion to be irradiated. The criteria for selection of the
therapeutic radionuclide would depend upon whether there is internalization of the administered
product in a lesion or surface uptake on the lesion. The concept of tailored therapy has also been
advocated. From practical point of view, it is convenient to classify the radionuclides as alpha
emitters, Auger/conversion electron emitters, hard beta emitters and soft beta emitters (Table 3).
It is possible to confine the delivery of dose over a range of few micrometers to several millimeters
(Table 3 and 6). Usually an index called, range for 90% of energy loss (‘X90’), is cited in the case
of beta particles, rather than the maximum or mean range in tissue.
Table 6: Salient features of the more important Therapeutic Radionuclides
RN T½ E (max.), Range in Tissue Major chemical characteristics/General remarks
MeV Max./mm.
32
P 14.3d 1.71 9 Versatile; organic/inorganic forms possible
33
P 25.3d 0.25 1
89
Sr 50.5d 1.46 8 Calcium analogue
90
Y 2.67d 2.27 12# M+3; versatile; 90Sr content limit problems.
153
Sm 46.3h 0.8 3 $ M+3; versatile, ease of production
166
Ho 1.1d 1.85 8 M+3; versatile, ease of production
169
Er 9.4d 0.34 1 M+3; soft beta; specific utility
177
Lu 6.73 d 0.49 1.5 M+3; versatile, ease of production
186
Re 3.7d 1.07 4.6 Tc analogue; Versatility
188
Re 17h 2.11 11 Tc analogue; Versatility, ‘nca’ form and generator
#X90 for 90Y is 5 mm $ X90 for
153
Sm is 1 mm
131
I, is a well established field the world
route possible.
Radioisotope generator (RIG) serves as the source for a few short-lived radionuclides used in
therapy {e.g. 90Sr (28.6y) - 90Y (64h);
225
Ac (10d) -
213
Bi (45.6 min)}. Unlike the RIG used for diagnostic applications, the separation
188
W (69.4d) -
188
Re (17h);
224
Ra (3.66d) -
212
Pb/
212
Bi (1h);
of the daughter nuclide and formulation of the therapeutic product will have to be invariably
carried out at the manufacturers’ end or in a centralized radiopharmacy. The stringent quality
control tests applicable in this case, especially tests to ensure that the breakthrough of parent
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