Sources of radionuclides

 

Sources of radionuclides[edit]

See also: Radiopharmacology

^99mTc is normally supplied to hospitals through a radionuclide generator containing the parent radionuclide molybdenum-99. ⁹⁹Mo is typically obtained as a fission product of ²³⁵U in nuclear reactors, however global supply shortages have led to the exploration of other methods of production. About a third of the world's supply, and most of Europe's supply, of medical isotopes is produced at the Petten nuclear reactor in the Netherlands. Another third of the world's supply, and most of North America's supply, was produced at the Chalk River Laboratories in Chalk River, Ontario, Canada until its permanent shutdown in 2018.^[16]

The most commonly used radioisotope in PET ¹⁸F, is not produced in any nuclear reactor, but rather in a circular accelerator called a cyclotron. The cyclotron is used to accelerate protons to bombard the stable heavy isotope of oxygen ¹⁸O. The ¹⁸O constitutes about 0.20% of ordinary oxygen (mostly oxygen-16), from which it is extracted. The ¹⁸F is then typically used to make FDG.

Common isotopes used in nuclear medicine ^[17][18][19]

isotope	symbol	Z	T1/2	decay	gamma (keV)	Beta energy (keV)
Imaging:
fluorine-18	18F	9	109.77 m	β+	511 (193%)	249.8 (97%)[20]
gallium-67	67Ga	31	3.26 d	ec	93 (39%), 185 (21%), 300 (17%)	-
krypton-81m	81mKr	36	13.1 s	IT	190 (68%)	-
rubidium-82	82Rb	37	1.27 m	β+	511 (191%)	3.379 (95%)
nitrogen-13	13N	7	9.97 m	β+	511 (200%)	1190 (100%)[21]
technetium-99m	99mTc	43	6.01 h	IT	140 (89%)	-
indium-111	111In	49	2.80 d	ec	171 (90%), 245 (94%)	-
iodine-123	123I	53	13.3 h	ec	159 (83%)	-
xenon-133	133Xe	54	5.24 d	β−	81 (31%)	0.364 (99%)
thallium-201	201Tl	81	3.04 d	ec	69–83* (94%), 167 (10%)	-
Therapy:
yttrium-90	90Y	39	2.67 d	β−	-	2.280 (100%)
iodine-131	131I	53	8.02 d	β−	364 (81%)	0.807 (100%)
lutetium-177	177Lu	71	6.65 d	β−	113 (6.6%), 208 (11%)	497 (78.6%), 384 (9.1%), 176 (12.2%)
Z = atomic number, the number of protons; T1/2 = half-life; decay = mode of decay photons = principle photon energies in kilo-electron volts, keV, (abundance/decay) β = beta maximum energy in mega-electron volts, MeV, (abundance/decay) β+ = β+ decay; β− = β− decay; IT = isomeric transition; ec = electron capture * X-rays from progeny, mercury, Hg

A typical nuclear medicine study involves administration of a radionuclide into the body by intravenous injection in liquid or aggregate form, ingestion while combined with food, inhalation as a gas or aerosol, or rarely, injection of a radionuclide that has undergone micro-encapsulation. Some studies require the labeling of a patient's own blood cells with a radionuclide (leukocyte scintigraphy and red blood cell scintigraphy). Most diagnostic radionuclides emit gamma rays either directly from their decay or indirectly through electron–positron annihilation, while the cell-damaging properties of beta particles are used in therapeutic applications. Refined radionuclides for use in nuclear medicine are derived from fission or fusion processes in nuclear reactors, which produce radionuclides with longer half-lives, or cyclotrons, which produce radionuclides with shorter half-lives, or take advantage of natural decay processes in dedicated generators, i.e. molybdenum/technetium or strontium/rubidium.

The most commonly used intravenous radionuclides are technetium-99m, iodine-123, iodine-131, thallium-201, gallium-67, fluorine-18 fluorodeoxyglucose, and indium-111 labeled leukocytes.^{[citation needed]} The most commonly used gaseous/aerosol radionuclides are xenon-133, krypton-81m, (aerosolised) technetium-99m.^[22]