Discuss one type of radioactive emission produced by radioactive isotopes (how it is created/decay mechanism). List an isotope that produces this type of radioactive emission. How does this particular radioactive particle make this isotope useful for therapy?
Though there are various decay mechanisms that radioactive isotopes go through to achieve a stable state, including alpha, beta (negatron and positron), electron capture, and isomeric transition, I will be reviewing negatron (β-) decay for this discussion. When a radionuclide has an excessive amount of neutrons or a high neutron to proton ratio, the radionuclide is said to be in an unstable state.[1] To achieve stability, it releases energy and matter. In the case of negatron decay, the neutron decays into a proton through the release of a negative electron (negatron particle) from the nucleus and an antineutrino.[1,2] The negatron particle does not exist inside the nucleus, rather, it is created through the process of decay.[2] An example of a radioisotope that undergoes negatron decay is Gold-198.
Gold-198 is most commonly used in the form of a seed, typically 2.5 mm long and an outer diameter of 0.8 mm, that is encapsulated in platinum and used for brachytherapy procedures.[1,2] Gold-198 became favored over radon-222 when it was found to cause less damage to the surrounding tissue because of its lower photon energy and because more of the dose was absorbed locally.[3] Because Gold-198 has such a short half-life, it is commonly used as permanent interstitial implants to treat prostate cancer. Since the seeds can be seen on radiographic images, they can be used as fiducial markers to align patients for external beam radiation therapy if they receive treatments after their brachytherapy. Although 198Au is most commonly used for prostate treatments, it is also being used to treat malignancies of the cervix, bladder, and skin, among others.[3]
References
Gold-198 is most commonly used in the form of a seed, typically 2.5 mm long and an outer diameter of 0.8 mm, that is encapsulated in platinum and used for brachytherapy procedures.[1,2] Gold-198 became favored over radon-222 when it was found to cause less damage to the surrounding tissue because of its lower photon energy and because more of the dose was absorbed locally.[3] Because Gold-198 has such a short half-life, it is commonly used as permanent interstitial implants to treat prostate cancer. Since the seeds can be seen on radiographic images, they can be used as fiducial markers to align patients for external beam radiation therapy if they receive treatments after their brachytherapy. Although 198Au is most commonly used for prostate treatments, it is also being used to treat malignancies of the cervix, bladder, and skin, among others.[3]
References
- Khan FM. The Physics of Radiation Therapy. 4th ed. Baltimore, MD: Lippincott, Williams, and Wilkins; 2010: 319.
- Brachytherapy: History and Review. [Softchalk]. La Crosse, WI: UW-L Medical Dosimetry Program; 2016
- Washington CM, Leaver DT. Principles and Practice of Radiation Therapy. St. Louis, MO: Mosby Elsevier; 2010:304-305.