9.1 International Consensus
Nomenclature Guidelines – Summary1
1Consensus nomenclature rules for radiopharmaceutical
chemistry — setting the record straight, Coenen, H.H., Gee A.D. et al., Nuclear
Medicine and Biology, Volume 55, v – xi (2017)
9.2 Measures of Radioactivity
(1) Unit of activity
- “Radioactivity” is a physical phenomenon, defined
as the property of certain nuclei to spontaneously fragment or rearrange, resulting
in the emission of radiation.
- “Activity”
is the quantitative measure of
radioactivity: The number of nuclear decays, occurring
in a given quantity of material over a certain time interval, divided by that
time interval.
- “Becquerel”
(Bq) is the agreed SI derived unit
for the quantity of activity.
- Pre-SI units
(e.g. imperial units) (e.g. mCi, Ci) can also be used, but must be placed in
parentheses after the stated SI units.
* N.B.: The correct terms “radioactive” and
“non-radioactive” must not be replaced by the lab-jargon “hot” and “cold”,
respectively, in public or official documents.
(2) Molar activity (Am) and specific activity (As)
- Molar
activity is the measured activity per
mole of compound; measured in Bq/mol (GBq/µmol).
- Specific
activity is the measured
activity per gram of compound;
measured in Bq/g (GBq/µg).
- Due to
radioactive decay, the instant of time of measurement must be stated; for
example: “The molar activity was 50 GBq/µmole 2 h after the end of synthesis”.
- Apparent molar activity and apparent specific
activity
The
terms apparent molar activity and apparent specific activity take
into account the amounts of the
labelled and non-radiolabelled
impurities present (using moles, or weight, respectively).
- Effective
molar activity and effective specific activity
The
terms “effective molar activity” and “effective specific activity” address the
chemically, biologically or pharmacologically ‘active’ fraction of radioactive
and non-radioactive materials in a sample, competing with the labelled product
in its chemical or biological reactions. In this case, the “effectivity” must
be determined by an additional analytical process; e.g. receptor or enzyme
binding assay, side-product analysis, etc. Other terms like “pseudo-specific activity”
etc. must not be used.
- ‘No-carrier-added’,
‘carrier added ’and ‘carrier-free’
The
non-quantitative terms, “no-carrier-added” (n.c.a.) and “carrier-added” (c.a.)
can be used as a practical, qualitative indication of specific or molar
activity. The term “carrier-free” (c.f.) can only be used in the rare case
where the theoretical maximum specific or molar activity is unambiguously
proven.
- Measures
involving determination of amounts of material (e.g. molar activity or
radiochemical purity), should be accompanied by a clear description of the
method of detection.
9.3 Radionuclide and Radioisotope Descriptors
The
enrichment of a chemical compound with an isotope (stable or radioactive) of
one or more of the elements, of which it is constituted, is indicated by the
symbol of the element (E) together with its mass number (A) (as a superscript
in front) within square brackets, [AE], immediately preceding the
compound’s name or chemical formula.
(1) For example, [2H,14C]benzene, or [2H,14C]C6H6,
represent the compound benzene,
enriched or labelled, with stable deuterium and radioactive carbon-14,
respectively.
(2) For rules designating labelling positions (e.g. L-[methyl-11C]methionine or L-[carboxyl-11C]methionine): see http://goldbook.iupac.org/pages/about.html.
(3) These rules apply equally to organic, inorganic and
organometallic compounds and complexes: e.g. [223Ra]RaCl2,
[99mTc]NaTcO4, [99mTc]Tc-MDP, [68Ga]Ga-DOTA-TATE,
etc.
(4) As square brackets are also used to denote
metal complexes, care should be taken to avoid confusion with radionuclide
descriptors: e.g. [99mTc][Tc(CO)3(OH2)3]+,
[111In][In(DTPA)]2-, etc.
* N.B.: The
symbol for isotopic enrichment [AE] should be treated like a
syllable, and thus only be hyphenated at the end of a line of text. Conversely,
do not use nuclide symbols in square brackets in combination with nouns and
verbs.
(5) Examples of the use of
square brackets and hyphens
- Correct - Incorrect
L-[13N]alanine,
(S)-[13N]alanine [13N]L-alanine,
(S)-13N-alanine, L-[13N]-alanine
[18F]fluorobenzene [18F]benzene
(no fluorine atom in benzene)
[99mTc]TcDTPA2- [99mTc]DTPA2-,
99mTc-DTPA2- (no Tc in chelator)
11C-compound, 125I-substitution, [11C]compound, [125I]-substitution,
18F-derivative, 68Ga-conjugate [18F]-derivative, [68Ga]conjugate (no
chemical compound names)
77Br-reagent
11C-labelling, 64Cu-labelling, [11C]labelling, [64Cu]-labelling,
18F-fluorination (with hyphen!) [18F]-(radio)-fluorination
(no chemical compound names)
- The terms ‘(radio)isotope’
and ‘(radio)nuclide’ are often used incorrectly in texts, inferring “isotope”
means “radioactive nuclide” or even “labelled compound”.
a) ‘Nuclide’
indicates an atom, characterised by its numbers of protons (identifying its
elemental nature) and of nucleons (indicating its mass).
b)‘Isotopes’ are nuclides of the same element (same proton number), but having
different numbers of neutrons (hence different atomic mass).
c) Isotopic
nuclides of different energy state are called isomeric nuclides, isomeric
isotopes or ‘isomers’, such as technetium-99g and -99m.
* N.B.: All (radio)isotopes are
(radio)nuclides, while the reverse is not true!
9.4 Radiochemical Yield (RCY)
(1) The “radiochemical yield” is
the amount of activity in the product expressed as the percentage (%) of
related starting activity utilized in the considered process (e.g. synthesis,
separation, etc.). The quantity of both must relate to the same radionuclide and be decay corrected to the same
point in time before the calculation is made (Reported
measures of RCY should indicate, whether a product was isolated or not.).
(2) Colloquial expressions for “radio-yield” found in
literature, e.g. ‘radiochemical conversion’, ‘analytical radiochemical yield’,
‘radio-HPLC yield’ must not be used as a surrogate for ‘radiochemical yield’ or
‘radiochemical purity’, respectively.
(3) The following text may serve as examples for good
practice, when describing a radiochemical yield:
- “The radiochemical yield was 67 % (based on HPLC analysis
of the crude product).”
- “The radiochemical yield* of “Y” was 67 %”, with the following as a footnote:
* “determined
by radio-HPLC analysis of the crude product” or
* “non-isolated, estimated by radio-HPLC”
- or, in the general experimental section: “All
radiochemical yields were determined by HPLC of the crude product, unless
stated otherwise.”
- or alternatively use: ‘The radiochemical purity of the
crude product was 67 %.”
- or: “The radiochemical yield of “Y” determined from an
aliquot of the reaction solution amounted to 67 %.”
- or: “The radiochemical yield of crude “Y” was 67 % based
on the amount of activity eluted from the HPLC column”
(4) Expressions such as ‘conversion’ or ‘incorporation’, however,
may be used in a semantic sense and even be indispensable in context of
mechanistic discussions. For example, “The ‘conversion’ (or ‘incorporation’)
proceeded with a 50 % yield. Here it is clear from the context, that the
radiochemical yield of the conversion is intended.
(5) Activity yield
- The “activity yield” is the amount of radioactive product
expressed in Bq (MBq, GBq), which is obtained from a
starting amount of activity (e.g. produced at a cyclotron) and is not corrected
for decay.
- This term is useful, or necessary to indicate the
efficiency of a labelling procedure. The activity yield is, of course, dependent on the
effectiveness and duration of all technical manipulations used, in addition to
the yield of the labelling reaction.
1For background and full discussion of these
recommendations, see source article:
Consensus nomenclature rules for radiopharmaceutical chemistry —
setting the record straight, Heinz
H. Coenen, Antony D. Gee, Michael Adam, Gunnar Antoni, Cathy S. Cutler, Yasuhisa
Fujibayashi, Jae Min Jeong, Robert H. Mach, Thomas L. Mindt, Victor W. Pike,
Albert D. Windhorst, Nuclear Medicine and Biology, Volume 55, v – xi
(2017)
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