Yttrium-90 () is a radioactive isotope of

yttrium Yttrium is a chemical element; it has Symbol (chemistry), symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and has often been classified as a "rare-earth element". Yttrium is almost a ...

. Yttrium-90 has found a wide range of uses in

radiation therapy Radiation therapy or radiotherapy (RT, RTx, or XRT) is a therapy, treatment using ionizing radiation, generally provided as part of treatment of cancer, cancer therapy to either kill or control the growth of malignancy, malignant cell (biology), ...

to treat some forms of

cancer Cancer is a group of diseases involving Cell growth#Disorders, abnormal cell growth with the potential to Invasion (cancer), invade or Metastasis, spread to other parts of the body. These contrast with benign tumors, which do not spread. Po ...

. Along with other

isotopes of yttrium Natural yttrium (39Y) is composed of a single isotope, yttrium-89. The most stable radioisotopes are 88Y, which has a half-life of 106.6 days, and 91Y, with a half-life of 58.51 days. All the other isotopes have half-lives of less than a day, exce ...

, it is sometimes called radioyttrium.

Decay

undergoes beta particles emissions/decay ( β⁻ decay) to zirconium-90 with a half-life of 64.1 hours and a decay energy of 2.28 MeV with an average beta energy of 0.9336 MeV. It also produces 0.01% 1.7 MeV

photon A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless particles that can ...

s during its decay process to the 0⁺ state of ⁹⁰Zr, followed by

pair production Pair production is the creation of a subatomic particle and its antiparticle from a neutral boson. Examples include creating an electron and a positron, a muon and an antimuon, or a proton and an antiproton. Pair production often refers ...

. The interaction between emitted

electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...

s and matter can lead to the emission of

Bremsstrahlung In particle physics, bremsstrahlung (; ; ) is electromagnetic radiation produced by the deceleration of a charged particle when deflected by another charged particle, typically an electron by an atomic nucleus. The moving particle loses kinetic ...

radiation.

Production

Yttrium-90 is produced by the nuclear decay of

strontium-90 Strontium-90 () is a radioactive isotope of strontium produced by nuclear fission, with a half-life of 28.79 years. It undergoes β− decay into yttrium-90, with a decay energy of 0.546 MeV. Strontium-90 has applications in medicine a ...

which has a half-life of nearly 29 years and is a

fission product Nuclear fission products are the atomic fragments left after a large atomic nucleus undergoes nuclear fission. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons, the releas ...

uranium Uranium is a chemical element; it has chemical symbol, symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Ura ...

used in nuclear reactors. As the strontium-90 decays, chemical high-purity separation is used to isolate the yttrium-90 before

precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwe ...

. Yttrium-90 is also directly produced by neutron activation of natural yttrium targets (Yttrium is mononuclidic in ⁸⁹Y) in a nuclear research reactor.

Medical application

⁹⁰Y plays a significant role in the treatment of

hepatocellular carcinoma Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer in adults and is currently the most common cause of death in people with cirrhosis. HCC is the third leading cause of cancer-related deaths worldwide. HCC most common ...

(HCC),

leukemia Leukemia ( also spelled leukaemia; pronounced ) is a group of blood cancers that usually begin in the bone marrow and produce high numbers of abnormal blood cells. These blood cells are not fully developed and are called ''blasts'' or '' ...

, and

lymphoma Lymphoma is a group of blood and lymph tumors that develop from lymphocytes (a type of white blood cell). The name typically refers to just the cancerous versions rather than all such tumours. Signs and symptoms may include enlarged lymph node ...

, although it has the potential to treat a range of tumors. Trans-arterial radioembolization is a procedure performed by interventional radiologists, in which ⁹⁰Y microspheres are injected into the arteries supplying the tumor. The microspheres come in two forms: resin, in which ⁹⁰Y is bound to the surface, and glass, in which ⁹⁰Y is directly incorporated into the microsphere during production. Once injected, the microspheres become lodged in blood vessels surrounding the tumor and the resulting radiation damages the nearby tissue. The distribution of the microspheres is dependent on several factors, including catheter tip positioning, distance to branching vessels, rate of injection, properties of particles, like size and density, and variability in tumor perfusion.

Radioembolization Selective internal radiation therapy (SIRT), also known as transarterial radioembolization (TARE), radioembolization or intra-arterial microbrachytherapy is a form of radionuclide therapy used in interventional radiology to treat cancer. It is gene ...

with ⁹⁰Y significantly prolongs time-to-progression (TTP) of HCC, has a tolerable adverse event profile, and improves patient quality of life more than do similar therapies. ⁹⁰Y has also found uses in tumor diagnosis by imaging the Bremsstrahlung radiation released by the microspheres.

Positron emission tomography Positron emission tomography (PET) is a functional imaging technique that uses radioactive substances known as radiotracers to visualize and measure changes in metabolic processes, and in other physiological activities including blood flow, r ...

after radioembolization is also possible.

Post-treatment imaging

Following treatment with ⁹⁰Y, imaging is performed to evaluate ⁹⁰Y delivery and absorption to evaluate coverage of target regions and involvement of normal tissue. This is typically performed using Bremsstrahlung imaging with single-photon emission computed tomography CT (SPECT/CT), or using ⁹⁰Y position imaging with positron emission tomography CT (PET/CT).

Bremsstrahlung imaging after ⁹⁰Y therapy

As ⁹⁰Y undergoes beta decay, broad spectrum

bremsstrahlung radiation In particle physics, bremsstrahlung (; ; ) is electromagnetic radiation produced by the deceleration of a charged particle when deflected by another charged particle, typically an electron by an atomic nucleus. The moving particle loses kinetic ...

is emitted and is detectable with standard gamma cameras or SPECT. These modalities provide information about radioactive uptake of ⁹⁰Y, however, there is poor spatial information. Consequently, it is challenging to delineate anatomy and thereby evaluate tumor and normal tissue uptake. This led to the development of SPECT/CT, which combines the functional information of SPECT with the spatial information of CT to allow for more accurate ⁹⁰Y localization.

Positron imaging after ⁹⁰Y therapy

PET/CT and PET/MRI have superior spatial resolution compared to SPECT/CT because PET detects positron pairs produced from the decay of emitted positrons, negating the requirement for a physical collimator. This allows for better assessment of microsphere distribution and dose absorption. However, both PET/CT and PET/MRI are less widely available and more costly.

References

External links

* {{Radiation oncology Isotopes of yttrium Medical isotopes