Nuclear Structure and Decay
Eric Ford in Primer on Radiation Oncology Physics, 2020
Some nuclei, particularly very heavy ones, undergo alpha decay (yellow boxes in Figures 2.1.1 and 2.2.3). A nucleus undergoing this decay produces an alpha particle, α, i.e. a particle with two protons and two neutrons which is the same as a helium nucleus, . An example of such a decay is shown in Figure 2.2.4, i.e. the decay of 226Ra (radium) into 222Rn (radon). In 94% of such decays the result is a nucleus that is in the ground-state of 222Rn, but 6% of the time the decay is into an excited state of 222Rn at a higher energy. This excited 222Rn nucleus then decays into the ground state of 222Rn, releasing a photon of energy 0.18 MeV in this case. Historically, 226Ra was often used in brachytherapy, and it was the 0.18 MeV photon that provided the therapeutic dose.
Basic Atomic and Nuclear Physics
K. N. Govinda Rajan in Radiation Safety in Radiation Oncology, 2017
Radioactivity was discovered by Becquerel while studying the properties of a uranium compound. Following the discovery of X-rays, he was trying to find out if uranium compound could emit some form of X-rays following the absorption of sunlight, but to his surprise he found the compound emitting some radiation (when it blackened a photographic plate), even without sunlight exposure. His experiments to deflect the radiations in a magnetic field showed one type deflecting to the right, one deflecting to the left and one not deflecting at all. He concluded that the emitted particles were carrying a positive charge, negative charge, and no charge, respectively. Not knowing the nature of the radiations, they were named as α, β, and γ radiations, by Rutherford. We now know that α is a helium nucleus, β is an electron, and γ is electromagnetic radiation. Madame Curie named the phenomenon radioactivity. When Curie extracted uranium from the ore and studied its activity, she found a lot more radioactivity and other radioactive elements in the ore. The subsequent studies revealed that all elements beyond lead were inherently unstable and were radioactive. The radioactivity emanates from the elements 238U, 235U, and 232Th resulting in a radioactive chain that ends in stable 206Pb, 207Pb, and 208Pb, respectively. All the uranium and thorium have not decayed by now because their half-lives are of the order of the age of the earth.
Radiation injuries
Jan de Boer, Marcel Dubouloz in Handbook of Disaster Medicine, 2020
There are three main types of radiations: – alpha (α) radiation, characterised by the emission of a helium nucleus (2 protons + 2 neutrons). It has great oxidising power.– beta (ß) radiation is the result of a transformation process within the nucleus: either a neutron transforming into a proton (accompanied by the emission of an electron e− giving ß− radiation) or a proton transforming into a neutron (accompanied by the emission of a positron e+ to give ß+ radiation). The oxidising power of beta radiation is weaker than that of alpha radiation.– gamma (γ) radiation or photon γ. It is not the result of a transformation within the nucleus. This type of radiation is electromagnetic – like x-rays or visible light -but the wavelength is much shorter so its energy is correspondingly greater. This type of radiation can be encountered alone or associated with the alpha and beta radiation.
The potential of PSMA-targeted alpha therapy in the management of prostate cancer
Published in Expert Review of Anticancer Therapy, 2020
Luca Filippi, Agostino Chiaravalloti, Orazio Schillaci, Oreste Bagni
The alpha emission consists of a positively charged particle, identical to the naked helium-4 (4He) nucleus, formed by two protons and two neutrons bound together, having an extremely greater mass as compared to that of beta particles. Alpha particle is monoenergetic, with emission ranging between 5 and 9 MeV and presents a linear track of 50–100 micron, which entails an almost exclusive radiation delivery to the target and the strictly neighboring cells [12]. Alpha particles are classified as high linear energy transfer (LET) radiation and represent effective ionizing agents. The main advantage of utilizing alpha radiations consists in their capability of inducing effects independently from the oxygenation status of the cell. It is well known that hypoxic tumors are three-fold less sensitive to radiations than well-oxygenated tissues, since low LET radiations mainly produce deoxyribonucleic acid (DNA) damages through water hydrolysis and free radical formation. On the contrary, this ‘oxygen effect’ is of minor relevance for high LET radiations, such as alpha particles.
Translational boron neutron capture therapy (BNCT) studies for the treatment of tumors in lung
Published in International Journal of Radiation Biology, 2019
Verónica Andrea Trivillin, Ayelén Serrano, Marcela A. Garabalino, Lucas Luis Colombo, Emiliano César Pozzi, Andrea Monti Hughes, Paula M. Curotto, Silvia Inés Thorp, Ruben O. Farías, Sara J. González, Silva Bortolussi, Saverio Altieri, Maria E. Itoiz, Romina F. Aromando, David W. Nigg, Amanda E. Schwint
Boron neutron capture therapy (BNCT) is a two-component treatment modality that involves the selective accumulation of a 10B compound in tumors followed by irradiation with a thermal or epithermal neutron beam. The 10B accumulated in the tumor cell captures a thermal neutron and releases two high linear energy transfer (LET) particles, an alpha particle and a recoiling 7Li nucleus (Locher 1936). These high LET particles have a range of ≈5–9 µm in tissue and are known to have a high relative biological effectiveness (RBE) (Gabel et al. 1984). Within this context, BNCT would potentially target tumor tissue selectively, mostly sparing normal tissue (Coderre and Morris 1999). The best way of optimizing the therapeutic efficacy of BNCT is to optimize tumor boron targeting. The international community devotes much effort and resources to the design and assessment of novel, tumor-seeking boron carriers that would achieve the necessary threshold of intracellular boron concentration and improve selective tumor targeting. In addition, a short and medium-term strategy would be to improve tumor boron targeting employing boron compounds approved for their use in humans to expedite the transference to a clinical scenario (Schwint and Trivillin 2015).
212Pb-conjugated anti-rat HER2/neu antibody against a neu-N derived murine mammary carcinoma cell line: cell kill and RBE in vitro
Published in International Journal of Radiation Biology, 2022
Ioanna Liatsou, Jing Yu, Remco Bastiaannet, Zhi Li, Robert F. Hobbs, Julien Torgue, George Sgouros
Yard et al. (2019), recently reported the median RBE at 37% survival for a large number of tumor cell lines, following exposure to 223Ra, as 9.7 with an interquartile range of 4.5 to 12. The alpha-particle energies emitted by 223Ra and its daughters include lower energy 5.6 to 5.7 MeV alphas, these are emitted at higher initial LETs than the higher energy 6 and 8.8 MeV alphas emitted by 212 Bi (Sgouros et al. 2010). The LET along the particle track determines the complexity of DNA double strand breaks and correspondingly the RBE. In addition, differences in the decay distribution relative to the cellular geometry could contribute to the differences in the RBE of 223Ra compared to that of antibody-conjugated Pb-212; unlike antibody-conjugated 212Pb, 223Ra is not localized on the cell surface or intracellularly. Ballangrud et al. (2004), reported radiosensitivity (absorbed dose for 37% survival) values for both low and high LET radiation (Cs-137 and 225Ac-conjugated antibody), respectively for three breast cancer cell lines, MCF7, MDA-MB-231 and BT-474. To obtain radiosensitivity to high LET radiation of the three cell lines that would not be influenced by binding to HER2/neu sites a nonspecific antibody was used. The RBE values calculated from the data provided in this study are 2.8, 2.6 and 4.7 for MCF-7, MDA-MB-231 and BT-474, respectively (Ballangrud et al. 2004).
Related Knowledge Centers
- Alpha Decay
- Beta Particle
- Ionizing Radiation
- Particle Radiation
- Penetration Depth
- Radioactive Decay
- Skin
- Atomic Nucleus
- Ion
- Ternary Fission