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Biochemical and Pharmacological Rationales in Radiotracer Design
Published in Lelio G. Colombetti, Principles of Radiopharmacology, 2019
Raymond E. Counsell, Nancy Korn
Nuclides popular for use in foreign labeling of organic compounds include selenium-75, and the halogens — fluorine-18, and bromine and iodine in several isotopic forms. Selenium-75 and fluorine-18 have been considered as bioisosteric replacements for sulfur and hydroxyl (or hydrogen), respectively.25 The many useful isotopic forms of iodine make this element especially versatile and widely used in nuclear medicine. Io-dine-125 is useful in preliminary animal studies due to its relatively long half-life (60 days) and low radiation energy (35 keV), which simplify synthesis, storage, and safety procedures. Replacement of iodine-125 with other more energetic isotopes of iodine (iodine-131 or iodine-123) can be done with relative ease. Bromine has been suggested as a substitution for methyl groups in organic molecules.25 While there are many nuclides of bromine with characteristics suitable for incorporation into radiotracers, only bromine-82 has been used to any extent clinically. It has not received much use, however, because of the high energy gammas associated with its decay. Recently, however, bromine-76 (T1/2 = 17 hr, positron emission) and bromine-77 (T½ = 57 hr, 30% 242 keV gamma) have become available and have considerable clinical promise.26,27
Radionuclide Generators
Published in Garimella V. S. Rayudu, Lelio G. Colombetti, Radiotracers for Medical Applications, 2019
The chemical problems are the most numerous and start with the isolation of the parent from the target material or its fission contaminants. Manipulating highly radioactive substances can be difficult, mainly because the purification involves minuscule amounts of materials. It has been calculated that the weight of a curie of any of the radionuclides used at the present time to prepare generators is in the 10-4 to 10-5 mg range.47 Sometimes it is very difficult to isolate the desired radionuclide from radioactive contaminants. For example, 123I produced by the 122Te(d,n)123I reaction is contaminated by several other isotopes of iodine (124I, 125I, 126I, 129I, 130I, 131I, 132I) and one of sodium (24Na).48 The contaminants that will be administered together with the main radionuclide result in a much higher radiation dose being absorbed by the patients than that expected in a pure radionuclidic sample.49, 50
Biokinetic Models
Published in Shaheen A. Dewji, Nolan E. Hertel, Advanced Radiation Protection Dosimetry, 2019
Recently the ICRP adopted an updated model for iodine (Leggett 2010) for use in upcoming revisions of ICRP documents on occupational intake of radioiodine. The updated model is intended to describe the iodine cycle in the human body in sufficient detail to provide improved dose estimates for short-lived isotopes of iodine that may be encountered in and around nuclear facilities or used in nuclear medicine.
Retinoblastoma and uveal melanoma in Jordan: incidence, demographics, and survival (2011-2020)
Published in Ophthalmic Genetics, 2023
Yacoub A. Yousef, Mona Mohammad, Ibrahim Al-Nawaiseh, Hala Mahafza, Hadeel Halalsheh, Mustafa Mehyar, Reem AlJabari, Khaleel Al-Rawashdeh, Imad Jaradat, Iyad Sultan, Maysa Al-Hussaini
The mean age at diagnosis for UM patients in Jordan and Saudi Arabia was 46 and 50 years respectively, compared to 60 years in the collaborative ocular melanoma study (COMS) for 1317 patients) (25); an almost 15 and 10 years older (59). There was a statistically insignificant slight, male predominance in our series, which concurs with the COMS randomized prospective study where no sex predilection was found (61). Before the introduction of plaque brachytherapy, enucleation was the primary treatment for UM, saving a life but sacrificing vision (62–64). The introduction of plaque brachytherapy has revolutionized UM management and resulted in greater cosmetic effect, globe preservation, and saving some vision in selected cases selected cases without compromising survival compared to enucleation, and the most popularly used radioactive isotopes are Iodine 125 (125I), Ruthenium 106 (106Ru), and Palladium 103 (103Pd) (65). The reported local recurrence rates after brachytherapy are 14.7% for 106Ru treatment, 7%–10% for 125I, and 3.3% for 103Pd (30,62,66). Unfortunately, mortality remains a big burden for metastatic disease, as there is no cure yet for metastatic UM (67).
Facts and ideas from anywhere
Published in Baylor University Medical Center Proceedings, 2020
When the operators of the nuclear plant realized that the top of unit 4 had disappeared and Soviet officials realized what had happened, the KGB cut intercity telephone lines to prevent information about the accident from spreading beyond the city of Prypiat. About an hour after the explosion, the radiation level in unit 4 exceeded 200 roentgens per hour. The ionizing radiation at Chernobyl was activated by the radioactive fission products blasted into the atmosphere by the explosion of the reactor. They included isotopes of iodine and cesium, as well as gases such as xenon-133. It was later estimated that the debris around the damaged reactor emanated radiation at a level of 10,000 roentgens per hour. That radiation level killed human cells or made them malfunction. Five hundred roentgens sustained over a period of 5 h meant certain death.