Radiopharmaceuticals selection of an isotope

Good evening! In fact, many factors are taken into account when choosing a nuclide for a radiopharmaceutical. The main requirement: the energy of a decay must be absorbed locally, and the irradiation of the entire organ must be minimal. Almost always short-lived nuclides are taken (half-life is from several minutes to several days). When choosing a nuclide, attention is also paid to the type of decay, radiation energy, specific activity, natural abundance of the parent nuclide, radiochemical purity, etc. Nuclides that undergo alpha and beta decay are usually chosen for therapy. For diagnostics, gamma radiation is used, but its energy shouldn't be very high in order to minimize the negative impact on the body

@elizaveta-msu do you have any manuals or instructions how to do this? Maybe there is some software?

@morphism To be honest, I'm not sure if there is any specific instruction for choosing a radionuclide. It seems to me that hospitals and clinics have a list of used radiopharmaceuticals and a proven technology for obtaining and using such radiopharmaceuticals. In research laboratories, it's a little more complicated.
I personally worked in the laboratory for some time with radiopharmaceuticals, and we synthesized peptide complexes with various nuclides. First, we selected nuclides according to their nuclear-physical characteristics (type of decay, half-life and radiation energy). Then the complexes were synthesized, the methods of obtaining such complexes were evaluated, then such parameters as the stability of the complex in blood serum, stability at human body temperature and above, and so on. That is, it was a rather painstaking work, and for each nuclide it's necessary to do a large number of experiments

as far as I know, a specific radionuclide is chosen taking into account also the size of the tumor against which the radiopharmaceutical will be used

@_brauer_ could you please give an example? 

@elizaveta-msu ok, sounds much more complicated than I've expected 😀 

@morphism by trial and error 🙂

@elizaveta-msu The main process in the science 😀 

@morphism exactly 🙂

@elizaveta-msu radionuclides emitting high-energy beta particles are useful for fighting large tumors, because in this case the high mileage compensates for the poor penetration of the radiopharmaceutical molecule into the tumor mass. But high-energy beta particles are ineffective for destroying small tumors, since the main energy of radioactive decay is absorbed in healthy tissues surrounding the tumor. Therefore, in the fight against small pathological areas and metastases, preference is given to alpha-emitters, and in the fight against individual cancer cells - to emitters of Auger electrons

I see on this forum a lot of topics dedicated to radiopharm devices, apparently the researchers are developing a stormy interest in this topic. The question arose, what types of rays should these drugs have? what radioactive isotopes are used or are promising for their creation?

@argentum Radiopharmaceuticals are really developing rapidly, since, on the one hand, they can be used for diagnostics, including detecting diseases at very early stages, on the other hand, radiopharmaceuticals are very effective in therapy, since they affect malignant tumors, practically without affecting healthy tissues of the body. About the choice of the type of decay and radiation energy you can read above - in short, for diagnostics gamma radiation is chosen, and for therapy are alpha and beta radiation. If we talk about nuclides used in radiopharmaceuticals, their set is quite wide, several dozen, I think. Of particular note is the isotopes of iodine, which are used for the diagnosis and treatment of thyroid diseases, isotopes of radium, which is similar to calcium and can be effective against diseases of the skeleton, radionuclides of many metals are used - Co-60, Cs-137, Tc-99m, etc.

@_brauer_ really interesting, thanks! I haven't heard about emitters of Auger electrons in radiopharmaceuticals

@elizaveta-msu @_brauer_ thank you very much for your answers! it seems to me, that the choice of a radionuclide is a really very painstaking work 🙂