Isotopes are atoms with the same number of protons but different numbers of neutrons from each other. Both stable and unstable isotopes exist, of which the latter shows characteristic radioactive decay through electromagnetic (gamma) or particle (α, β, Auger, etc.) emission.
Nuclear medicine includes imaging techniques single-photon emission computed tomography (SPECT) and positron emission tomography (PET), as well as therapeutic interventions brachytherapy, radioembolization and target-in radionuclide therapy (TIRT).Medical isotopes are also used for some types of external beam radiotherapy (EBRT) .Nuclear medicine physicians rely on the use of a dozen different isotopes that are matched to different applications based on their chemical and radioactive decay characteristics.
Radioisotopes can be prepared by means of nuclear reactors, accelerators, separation and extraction from nuclear fuel treatment waste streams, generators, etc. Currently, more than 80% of medical radioisotopes are produced by research reactors. Other medical isotopes can be prepared by particle accelerators, mainly cyclotron, linear accelerator or other methods.
Radioactive radiation of some isotopes can be used for treatment, especially cancer treatment. For example, radioisotopes that emit intense α or β- ion radiation can be used to destroy tumors.
Medical isotopes and generators under research:
225Ac is a high energy α Emission of radioisotopes has attracted more and more attention in the clinical research of targeted radiopharmaceutical therapy (RPT). RPT combines selected molecules with therapeutic radioisotopes (such as 225Ac) to directly target and deliver therapeutic dose of radiation to destroy cancer cells of cancer patients. 225Ac carries enough radiation to cause cell death in local areas of target cancer cells, and its half-life characteristics reduce additional radiation damage to patients. Due to the limitation of current production technology, the clinical research and commercial use of 225Ac have been restricted by insufficient supply for a long time.
The radionuclide, 213Bi, is a decay product of another promising alpha emitter 225Ac.
In general 225Ac/213Bi generators based on AG MP-50 cation exchange resin are most established and have been used for all patient studies with 213Bi to date. Other Single or multiple columns generators based on extraction chromatographic, ion exchange, and inorganic sorbents are also available.
212Pb is a member of the uranium-232 (232U) and thorium-232 (232Th) decay chain, and is commonly produced by the decay of 228Th (t1/2=1.9y) and radium-224 (224Ra, t1/2=3.64days).
Many 228Th generators exploit the chemical or physical separation of the daughters 224Ra and radon-220 (220Rn, t1/2=55.6s) by using cation exchange columns or chamber walls, and glass bubblers, respectively. 212Pb has been collected using nitric or hydrochloric acid or water to give yields of 85–90%. However, many of the 228Th generators reported to date have difficulty providing practical quantities of 212Pb due to the radiolytic damage to the generator matrix material when higher levels of activity are included.
To circumvent this, 224Ra generators have been used to produce 212Pb by separating 224Ra from 228Th on an anion exchange resin , followed by loading onto a cation exchange resin, actinide resin, or Pb-selective extraction resin, from which 212Pb is eluted using HCl or a complexing agent.