Stable
isotope
162
Er
164
Er
166
Er
167
Er
168
Er
170
Er
Relative
atomic mass
161.928 79
163.929 21
165.930 30
166.932 05
167.932 38
169.935 47
Mole
fraction
0.001 39
0.016 01
0.335 03
0.228 69
0.269 78
0.149 10
Erbium isotopes in biology
Radiolabeled 171Er tablets have been used to study bowel movements of individuals using
external scintigraphy. These tablets are made using enteric coated (coating that delays the
release of medication until after it has passed through the stomach) tablets that contain small
amounts of stable erbium oxide (170Er ) and irradiating them in a small neutron flux to produce
radioactive labeled 171 Er tablets, via the 170Er (n, γ) 171Er reaction. This method is a noninvasive
approach for determining gastric emptying rates and visualizing segments of the digestive system
in an individual [484, 485].
Erbium isotopes in medicine
169
Er is used in radiosynovectomy, which is a regularly practiced radiotherapy, on rheumatoid
arthritis patients whose condition is resistant to standard methods of treatment (Figure 1).
Rheumatoid arthritis is a chronic, inflammatory, autoimmune disease of the joint capsule
(synovial sac), which is lined with a thin membrane called the synovium, of an individual’s
moveable joints (synovial joints). In radiosynovectomy, the radiopharmaceutical called 169 Ercitrate colloid, which contains colloidal particles that are labeled with β-emitting 169Er, is directly
injected into the synovial cavity of the affected joint. These radioactive-colloid particles are then
phagocytized (engulfed) by macrophage-like synoviocytes as well as other phagocytizing
inflammatory cells in the patient’s synovium. Necrosis (tissue death) and the inhabitation of cell
proliferation (increase in number of cells) result from the radiation of the synovium and
therefore, temporarily halts synovitis (which is the condition of when the synovium thickens with
inflammation) and improves synovial joint function [486-489].
Fig. 1: Normal joint (top) vs. joint affected by rheumatoid arthritis (bottom) modified from
[490]).
Glossary
atomic number (Z) – The number of protons in the nucleus of an atom.
electron – elementary particle of matter with a negative electric charge and a rest mass of about
9.109 × 10–31 kg.
element (chemical element) – a species of atoms; all atoms with the same number of protons in
the atomic nucleus. A pure chemical substance composed of atoms with the same number of
protons in the atomic nucleus [703].
gamma camera (scintillation camera or Anger camera) – instrument used to track the
distribution in body tissue of radioactive isotopes (tracers) that emit gamma radiation (high
energy photons), a technique known as scintigraphy.
gamma rays (gamma radiation) – a stream of high-energy electromagnetic radiation given off
by an atomic nucleus undergoing radioactive decay. The energies of gamma rays are higher
than those of X-rays; thus, gamma rays have greater penetrating power.
half-life (radioactive) – the time interval that it takes for the total number of atoms of any
radioactive isotope to decay and leave only one-half of the original number of atoms.
isotope – one of two or more species of atoms of a given element (having the same number of
protons in the nucleus) with different atomic masses (different number of neutrons in the
nucleus). The atom can either be a stable isotope or a radioactive isotope.
neutron – an elementary particle with no net charge and a rest mass of about 1.675 × 10–27 kg,
slightly more than that of the proton. All atoms contain neutrons in their nucleus except for
protium (1H). [return]
proton – an elementary particle having a rest mass of about 1.673 × 10–27 kg, slightly less than
that of a neutron, and a positive electric charge equal and opposite to that of the electron. The
number of protons in the nucleus of an atom is the atomic number.
radioactive decay – the process by which unstable (or radioactive) isotopes lose energy by
emitting alpha particles (helium nuclei), beta particles (positive or negative electrons), gamma
radiation, neutrons or protons to reach a final stable energy state.
radioactive isotope (radioisotope) – an atom for which radioactive decay has been
experimentally measured (also see half-life).
radiolabeled – a mixture of an isotopically unmodified compound with one or more analogous
radioactive isotopically substituted compound(s). [return]
radiopharmaceutical – radiolabeled compound used for diagnostic or therapeutic purposes.
[return]
radiotherapy (radiation therapy) – the treatment of disease by means of radiation from
radioactive substances or X-rays. [return]
radiosynovectomy – a procedure using radioactive isotopes therapeutically to provide relief
from a condition in which the synovial membrane, which encloses each joint and secretes a
lubricating fluid to enable ease of joint motions, has become inflamed and irritated. [return]
scintigraphy – see gamma camera. [return]
stable isotope – an atom for which no radioactive decay has ever been experimentally measured.
tracer - substance used for tracking purposes.
X-rays – electromagnetic radiation with a wavelength ranging from 0.01 to 10 nanometers—
shorter than those of UV rays and typically longer than those of gamma rays.
References
484. A. Parr, Beihn, R.M., and Jay, M. International Journal of Pharmaceutics. 32 (2-3 ), 251
(1986).
485. M. C. Theodorakis. American Physiological Society, Gastrointestinal and Liver
Physiology. 239 (1), G39 (1980).
486. F. M. van der Zanta, Jahangierb, Z.N., Gommansa, G.G.M., Moolenburghc, J.D., and
Jacobsb, J.W.G. Applied Radiation and Isotopes. 65 (6), 649 (2007).
487. S. J. Kim, and Jung, K.A. Clinical Medicine & Research. 5 (4), 244 (2007).
488. M. E. A. McNeil. The first year rheumatoid arthritis: an essential guide for the newly
diagnosed. Marlowe & Company, New York, NY (2005).
489. G. Prabhakar, Sachdev, S.S., and Sivaprasad, N. Pharma Times. 41 (6), 11 (2009).
490. (N. J. V. J. A. b. R. Arthritis, ed.). National Institute of Arthritis and Musculoskeletal and
Skin Diseases, National Institutes of Health (2005).
703. I. U. o. P. a. A. Chemistry. Compendium of Chemical Terminology, 2nd ed. (the "Gold
Book"). Blackwell Scientific Publications, Oxford (1997).