Isotope Factoids Flashcards
In-111
Indium-111 is an isotope of indium with a radioactive half-life of 2.80 days, making it useful as a radioactive tracer. It is made for this use by the Nordion(Canada) Inc. unit of Nordion, Inc. as indium-111 chloride solution, and shipped to several firms which sterilize the pure solution, combine it with carrier compounds if needed, and repackage it for medical and industrial uses.
Among the medical applications of indium-111 are specialized diagnostic uses:
- indium-111 labeled antibodies;
- indium-111 oxine is also useful for isotopic labeling of blood cell components, specifically
- the labeling of platelets for indium-111 for thrombus detection and
- indium-111 labelled leukocytes for localization of inflammation and abscesses, and determination of leukocyte kinetics; [1]
- labeling of peptides and other proteins with indium-111 to determine their uptake by rare cancers (for example, the indium-111 octreotide scan is a highly specific and powerful tool for diagnosing carcinoid tumors, paragangliomas, some ectopic pheochromocytomas and other uncommon neuroendocrine tumors).[2]
Indium-111 decays by electron capture to cadmium-111, emitting a 0.1713 and 0.2454 MeV [3] gamma rays with a 2.8047 day radioactive half-life. The parent isotope of indium-111 is tin-111, with a decay mode of electron capture. Indium-111 also undergoes isomeric transition, emitting a 0.537 MeV gamma ray with a 7.7 minute half-life.[4]
Tc-99m
Technetium-99m when used as a radioactive tracer can be detected in the body by medical equipment (gamma cameras). It is well suited to the role because it emits readily detectable 140 keV gamma rays (these 8.8pm photons are about the same wavelength as emitted by conventional X-ray diagnostic equipment) and its half-life for gamma emission is 6.0058 hours (meaning 93.7% of it decays to 99Tc in 24 hours). The “short” physical half-life of the isotope and its biological half-life of 1 day (in terms of human activity and metabolism) allows for scanning procedures which collect data rapidly but keep total patient radiation exposure low. The same characteristics make the isotope suitable only for diagnostic but never therapeutic use.
Ga-67
Gallium-67 citrate is produced by a cyclotron. Charged particle bombardment of enriched Zn-68 is used to produce gallium-67. The gallium-67 is then complexed with citric acid to form gallium citrate. The half life of gallium-67 is 78 hours. It decays by electron capture, then emits de-excitation gamma rays that are detected by a gamma camera.
Gallium-67 photopeaks:
Energy Abundance 93 keV 40% 184 keV 20% 300 keV 17% 393 keV 5% The body generally handles Ga3+ as though it were ferric iron (Fe-III), and thus the free isotope ion is bound (and concentrates) in areas of inflammation, such as an infection site, and also areas of rapid cell division. Gallium (III) (Ga+3) binds to transferrin, leukocyte lactoferrin, bacterial siderophores, inflammatory proteins, and cell-membranes in neutrophils, both living and dead.
This relatively nonspecific gallium binding allows sites with tumor, inflammation, and both acute and chronic infection to be imaged by nuclear scan techniques.
I-123
odine-123 (123I or I-123) is a radioactive isotope of iodine used in nuclear medicine imaging, including single photon emission computed tomography (SPECT). The isotope’s half-life is 13.22 hours; the decay by electron capture to tellurium-123 emits gamma radiation with a predominant energy of 159 keV (this is the gamma primarily used for imaging). In medical applications, the radiation is detected by a gamma camera. The isotope is typically applied as iodide-123, the anionic form.
Iodine-123 is produced in a cyclotron by proton irradiation of xenon in a capsule.
The Auger electrons from the radioisotope have been found in one study to do little cellular damage, unless the radionuclide is incorporated chemically directly into cellular DNA, which is not the case for present radiopharmaceuticals which use I-123 as the radioactive label nuclide. The damage from the more penetrating gamma radiation and 127 keV internal conversion electron radiation from the initial decay of Te-123 is moderated by the relatively short half-life of the isotope.
123I is supplied as sodium iodide (NaI), sometimes in basic solution in which it has been dissolved as the free element. This is administered to a patient in capsule form, by intravenous injection, or (less commonly due to problems involved in a spill) in a drink. (131I is usually administered in a drink, due to the heavy radiation dose to local tissues which results before a capsule could dissolve).[6] The iodine is taken up by the thyroid gland and a gamma camera is used to functional images of the thyroid for diagnosis. Quantitative measurements of the thyroid can be performed to calculate the iodine uptake (absorption) for the diagnosis of hyperthyroidism and hypothyroidism. Dosing can vary; a small dose can start at 11.1 MBq [300 µCi],[5] while it is commonly an amount such as 2-4 mCi. There is a study that indicates a given dose can effectively result in effects of an otherwise higher dose, due to impurities in the preparation.[7] The dose of radioiodine 123I is typically tolerated by individuals who may be otherwise allergic to iodine, such as those who cannot tolerate contrast mediums containing larger doses of iodine such as used in CT scan, intravenous pyelogram (IVP) and similar imaging diagnostic procedures. Elsewhere it has been stated that iodine is not an allergen.[8]
Tl-201
201Tl (half-life 73 hrs), decays by electron capture, emitting Hg X-rays (~70–80 keV), and photons of 135 and 167 keV in 10% total abundance;[5] therefore it has good imaging characteristics without excessive patient radiation dose. It is the most popular isotope used for thallium nuclear cardiac stress tests.[8]
A thallium stress test is a form of scintigraphy, where the amount of thallium in tissues correlates with tissue blood supply. Viable cardiac cells have normal Na+/K+ ion exchange pumps. The Tl+ cation binds the K+ pumps and is transported into the cells. Exercise or dipyridamole induces widening (vasodilation) of normal coronary arteries. This produces coronary steal from areas where arteries are maximally dilated. Areas of infarct or ischemic tissue will remain “cold”. Pre- and post-stress thallium may indicate areas which will benefit from myocardial revascularization. Redistribution indicates the existence of coronary steal and the presence of ischemic coronary artery disease.[41]
Cs-137
Caesium-137 has a half-life of about 30.17 years.[1] About 95 percent decays by beta emission to a metastable nuclear isomer of barium: barium-137m (137mBa, Ba-137m). The remainder directly populates the ground state of barium-137, which is stable. Ba-137m has a half-life of about 153 seconds, and is responsible for all of the emissions of gamma rays in samples of caesium-137. One gram of caesium-137 has an activity of 3.215 terabecquerel (TBq).[3]
Accidental ingestion of caesium-137 can be treated with Prussian blue, which binds to it chemically and reduces the biological half-life to 30 days.[20]
Co-57
PHYSICAL CHARACTERISTICS: HALF-LIFE: 271 days. TYPE DECAY: e- capture gamma: 0.014 MeV (9.54 %). 0.122 MeV (85.6 %). 0.136 MeV (10.6 %).
Cobalt-57 (Co-57 or 57Co) is a radioactive metal that is used in medical tests; it is used as a radiolabel for vitamin B12 uptake. It is useful for the Schilling test.[2]
Co-60
Cobalt-60, 60Co, is a synthetic radioactive isotope of cobalt with a half-life of 5.2714 years. It is produced artificially by neutron activation of the isotope 59Co.[3] 60Co decays by beta decay to the stable isotope nickel-60 (60Ni). The activated nickel nucleus emits two gamma rays with energies of 1.17 and 1.33 MeV, hence the overall nuclear equation of the reaction is
Ba-133
Half Life: 10.51 years Radiation: Decay Mode: Electron Capture Gamma Constant: 2.4 mR/hr per 1 mCi at 30 cm Max. Beta Range in Air : N/A Max. Beta Range in Water : N/A cm Major Gammas: E(MeV). # per 100 Dis 0.081. 31.06 0.303. 18.33 0.356. 62.05 Average gamma E = 0.266 MeV
Y-90
90Y undergoes β− decay to zirconium-90 with a half-life of 64 hours and a decay energy of 2.28 MeV.[3] It also produces 0.01% 1.7 MeV[4] photons along the way. Interaction of the emitted electrons with matter can lead to Bremsstrahlung radiation.
TheraSphere®
• MDS Nordion, Canada
• Glass
• Yttrium-90
• Size = 25-35 microns
• doses = 3-20 GBq
• # spheres/tx = 1.2-8 mil
• Specific grav = >2
• FDA approved: HCC
• SIR-Spheres®
• Sydney, Australia
• Resin
• Yttrium-90
• Size = 20-40 microns
• dose = 3 GBq
• # spheres/tx = 40-80 million • Specific grav = < 1.8
• FDA approved: colorectal
There is no simple way to know precisely the radiation dose delivered to tumours and normal liver when SIR-Spheres microspheres are implanted because yttrium-90 only emits pure beta radiation with limited penetration range in tissue. The deposited dose is highly dependent on the distribution of microspheres and this cannot be known with any great precision other than by microscopic examination of tissue after implantation has occurred. Such analyses do confirm that tumours receive a lethal dose of radiation while the average dose to normal tissue is well below harmful levels. This approach, however, is clearly not appropriate for treatment planning purposes.
In general, 1 GBq (27 mCi) of yttrium-90/kg of tissue provides the equivalent of 50 Gy of radiation dose. However, because of the non-uniform distribution of the dose between the tumour and the normal liver tissue, a proportionally larger amount of radiation will be delivered to the tumour tissue.
The method used in clinical practice to calculate the patient-specific activity with SIR-Spheres microspheres is based on extensive clinical experience, both within and outside clinical studies. Please refer to the package insert or speak to your local Sirtex representative for further information on the appropriate method of dose calculation.
TV-MAA is injected in the liver to assess shunt patency to ensure y-90 is not delivered to stomach or bowel
I-131
I-131 decays with a half-life of 8.02 days with beta minus and gamma emissions. This nuclide of iodine has 78 neutrons in its nucleus, while the only stable nuclide, 127I, has 74. On decaying, 131I most often (89% of the time) expends its 971 keV of decay energy by transforming into the stable 131Xe (Xenon) in two steps, with gamma decay following rapidly after beta decay:
The primary emissions of 131I decay are thus electrons with a maximal energy of 606 keV (89% abundance, others 248–807 keV) and 364 keV gamma rays (81% abundance, others 723 keV).[11] Beta decay also produces an antineutrino, which carries off variable amounts of the beta decay energy. The electrons, due to their high mean energy (190 keV, with typical beta-decay spectra present) have a tissue penetration of 0.6 to 2 mm.[12]
Iodine-131 can be “seen” by nuclear medicine imaging techniques (i.e., gamma cameras) whenever it is given for therapeutic use, since about 10% of its energy and radiation dose is via gamma radiation. However, since the other 90% of radiation (beta radiation) causes tissue damage without contributing to any ability to see or “image” the isotope, other less-damaging radioisotopes of iodine are preferred in situations when only nuclear imaging is required.
Most I-131 production is from nuclear reactor neutron-irradiation of a natural tellurium target. Irradiation of natural tellurium produces almost entirely I-131 as the only radionuclide with a half-life longer than hours, since most lighter isotopes of tellurium become heavier stable isotopes, or else stable iodine or xenon.
Ra-223
Radium-223 (Ra-223) is an isotope of radium with an 11.4-day half-life, in contrast to the common isotope radium-226, discovered by the Curies, which has a 1601-year half-life. The principal use of radium-223, as a radiopharmaceutical to treat metastatic cancers in bone, takes advantage of its chemical similarity to calcium, and the short range of the alpha radiation it emits.
The use of radium-223 to treat metastatic bone cancer relies on the ability of alpha radiation from radium-223 and its short-lived decay products to kill cancer cells. Radium is preferentially absorbed by bone by virtue of its chemical similarity to calcium, with most radium-223 that is not taken up by the bone being cleared, primarily via the gut, and excreted. Although radium-223 and its decay products also emit beta and gamma radiation, over 95% of the decay energy is in the form of alpha radiation.[1] Alpha radiation has very short range in tissues, around 2-10 cells, compared to beta or gamma radiation. This reduces damage to surrounding healthy tissues, producing an even more localized effect than the beta-emitter strontium-89, also used to treat bone cancer. Taking account of its preferential uptake by bone and the alpha particles’ short range, radium-223 is estimated to give targeted osteogenic cells a radiation dose at least 8 fold higher than other non-targeted tissues[2]
Radium-223 has been developed by the Norwegian company Algeta ASA, in a partnership with Bayer, under the trade name Xofigo (formerly Alpharadin), and is distributed as a solution containing radium-223 chloride (1000 kBq/ml), sodium chloride, and other ingredients for intravenous injection. The recommended regimen is six treatments of 50 kBq/kg (1.3 uCi per kg), repeated at 4-week intervals.[2]
