ENTRIES A–Z
Philip Winn in Dictionary of Biological Psychology, 2003
Isotopes are variants of the same ELEMENT. Every ATOM of a particular element contains the same number of protons, but some have more neutrons (and therefore weigh more; see ATOMIC WEIGHT). Isotopes are very common in nature: most elements of biological importance have several isotopes. For example, carbon always has 6 protons, but can have 6, 7 or 8 neutrons. While these all have different atomic weights they are nevertheless isotopes of each other. Isotopes can be stable or radioactive: stable isotopes are those whose atomic nuclei remain stable: they have a number of protons and neutrons and retain those numbers. A radioactive isotope (or RADIOISOTOPE) is one in which the atomic nucleus decays, releasing protons and energy and, because protons are lost, turning the element from one thing to another. There is a received style for presenting elements that indicates their nuclear composition: carbon-12 has a total of 12 neutrons and protons. Since all forms of carbon have 6 protons, it follows that carbon-12 (or 12C, or 12/6C} has 6 neutrons. Carbon-13, by the same arithmetic, has 7 neutrons, carbon-14 has 8. Carbon-12 and carbon-13 are stable; carbon-14 is radioactive and decays over time to form nitrogen. Radioisotopes are useful in a variety of neuroscientific procedures: see for example, AUTORADIOGRAPHY; FUNCTIONAL NEUROIMAGING; RADIOIMMUNOASSAY; RADIOLABEL.
Radioactivity and Radiotracers
Graham Lappin, Simon Temple in Radiotracers in Drug Development, 2006
The nucleus is held together by the binding energy of the nucleus. Providing the binding energy exceeds the repulsive force between the positively charged protons, an equilibrium exists and the nucleus is stable. The presence of neutrons however, can upset the equilibrium and the atomic nucleus may become unstable. Although somewhat simplified, as a general rule the nucleus will become unstable when the number of protons and neutrons are uneven (Z ≠ N) resulting in incomplete spin-pairing. For example, deuterium (2H) has an equal number of protons and neutrons and is stable. Tritium (3H) however, contains two neutrons and one proton, and over time tritium decays to a more energetically-stable configuration and in the process releases radioactivity (Figure 2.1). Isotopes that undergo nuclear decay and emit radioactivity are known as radioisotopes. An atomic species whose nucleus is radioactive is known as a radionuclide.
Tests and procedures
Sarah Bekaert in Women's Health, 2018
In a bone scan, a radionuclide is used which accumulates in areas where there is a lot of bone activity (i.e. where bone cells are breaking down or parts of the bone are being repaired). This type of scan can therefore be used to detect areas of bone where there is cancer, infection or damage. These areas of activity are seen as ‘hot spots’ on the scan image. A radionuclide (sometimes called a radioisotope or isotope) is a chemical that emits a type of radioactivity known as gamma rays. A tiny amount of radionuclide is introduced into the body, usually by injection into a vein (sometimes it is breathed in or swallowed, depending on the test). Gamma rays are similar to X-rays and are detected by means of a device called a gamma camera. The gamma rays that are emitted from inside the body are detected by the gamma camera and converted into an electrical signal which is then sent to a computer. The computer builds a picture by converting the different intensities of radioactivity emitted into different colours or shades of grey. For example, areas of the target organ or tissue which emit high levels of gamma rays may be shown as red spots on the picture on the computer monitor, areas that emit low levels of gamma rays may be shown as blue spots, and various other colours may be used to show intermediate levels of gamma rays emitted.
The Impacts of Episcleral Plaque Brachytherapy on Ocular Motility
Published in Journal of Binocular Vision and Ocular Motility, 2021
Kaveh Abri Aghdam, Mostafa Soltan Sanjari, Masood Naseripour, Navid Manafi, Ahad Sedaghat, Shohreh Bakhti
Intraocular tumors impose a great risk on the sight and life of patients and they can arise from different eye structures. The most common primary intraocular neoplasms include choroidal melanoma and choroidal hemangioma in adults, and retinoblastoma in children.1–4 The aim of therapy for malignant ocular tumors is to offer the best prognosis for patient survival, globe retention, and sight preservation.5–9 Brachytherapy is used for the treatment of uveal melanoma, choroidal osteoma and hemangioma, retinoblastoma, capillary hemangioma, vasoproliferative tumor, conjunctival lymphoma, and even choroidal metastasis.9–15 Furthermore, for small to the middle-sized ciliary body and choroidal melanomas, episcleral plaque brachytherapy is the most widely used treatment modality.10 While ionizing radiation has a strong effect on intraocular tumors, it also has multiple destructive effects on adjacent normal tissues. Therefore, it is necessary to give a sufficient dose to the affected tissue while protecting the adjacent areas from the destructive radiation. Brachytherapy is a suitable option for this means.9,10 Radium-226, Cobalt-60, Ruthenium-106, Iodine-125, palladium-103, and strontium-90 are common radioisotopes used for this purpose. The usual dose in brachytherapy is between 0.4 to 1 Gy/h.9,10 A similar dose of different isotopes does not have a similar biologic effect on tissues.10
Radiolabeled mAbs as Molecular Imaging and/or Therapy Agents Targeting PSMA
Published in Cancer Investigation, 2018
Dimitrios Psimadas, Varvara Valotassiou, Sotiria Alexiou, Ioannis Tsougos, Panagiotis Georgoulias
Systemic delivery of cytotoxic radiation by specific cell-targeting via a radiolabeled Ab (RIT) is an attractive way to increase the tumor-delivered dose and decrease adverse effects in non-target tissue, which is critical in cancer treatment. Depending on the size of the targeted tumors, radioisotopes with different modes of decay may be used. The concept is that they should emit particle radiation that can destroy tumor cells either from a relative distance of some millimeters (β particles) or by entering the nucleus (α particles, Auger e−). The most common “therapeutic” radioisotopes are 90Y, 177Lu, 153Sm, and more. A major advantage of radiolabeled Abs for therapy purposes is that it is not necessary to bind to every tumor cell to induce cytotoxicity, since most therapeutic radioisotopes can be effective for several cell diameters due to the “crossfire effect”. In that way, radiation can destroy the Ag-negative cells as well, thus overcoming the problem of heterogeneity. The disadvantage of the above is that adjacent normal cells are also harmed due to radiation exposure, which is crucial for radiosensitive tissues such as the bone marrow.
Piflufolastat F-18 (18F-DCFPyL) for PSMA PET imaging in prostate cancer
Published in Expert Review of Anticancer Therapy, 2022
Andrew F. Voter, Rudolf A. Werner, Kenneth J. Pienta, Michael A. Gorin, Martin G. Pomper, Lilja B. Solnes, Steven P. Rowe
The biggest near-term change in use of PSMA-PET will be improved access. While 68Ga-PSMA-11 has seen use in Europe, access in the United States was limited, available only at select academic centers. Gallium-68 is challenging to produce in large quantities and has a relatively short half-life, limiting distribution options. In 2021, the FDA approved 18F-DCFPyL without location restrictions [4], as well as a commercial kit for generation of 68Ga-PSMA-11 [93]. As fluorine-18 production and distribution networks are more mature than those for gallium-68, this will greatly broaden access to these important imaging agents. Furthermore, clinical trials are currently underway for a range of other PSMA imaging agents, including PSMA-1007 [94], CTT1057 [95], and PSMA I&T [96], among others. As the underlying mechanism of action for all PSMA-targeted small-molecule agents is the same, similar overall performance is expected [97]. Nevertheless, clinical trials may reveal unique features of some of these agents. Furthermore, each radioisotope has its own set of benefits and challenges, and access to a set of clinically approved agents with a range of radioisotopes can only serve to improve access in diverse clinical settings.
Related Knowledge Centers
- Alpha Particle
- Beta Particle
- Cyclotron
- Gamma Ray
- Ionizing Radiation
- Particle Accelerator
- Radioactive Decay
- Internal Conversion
- Half-Life
- Radionuclide Generator