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New production method promises to end medical radioisotope shortages

Date:
April 21, 2022
Source:
University of Tokyo
Summary:
Technetium-99m is the world's most commonly used medical radioisotope, but regularly suffers from supply chain shortages, threatening the ability of doctors to diagnose a raft of ailments. But an alternative production technique looks set to make the radioisotope much more easily produced.
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FULL STORY

A commonly used radioisotope, technetium-99m, used in medical diagnoses regularly suffers from shortages due to being produced at aging nuclear reactors that often shut down for repairs. But an alternative technique for producing the isotope, developed by a group of researchers at the University of Tokyo and that takes advantage of equipment commonly found in hospitals, promises to bring an end to such supply chain frustrations.

A paper describing the method and its effectiveness in mice test subjects was recently published in the journalNuclear Medicine Biology.

Technetium-99m (99mTc) is one of the most commonly used medical radioisotopes in the world, thanks to the unique properties of its radioactivity. It emits gamma rays of moderate energy that are easily detectable by medical equipment.99mTc also has a moderately short half-life that allows its gamma emissions to be used as a tracer in medical diagnostic procedures while keeping patient radiation exposure very low.

This radioisotope is produced from molybdenum-99 (99密苏里州)产生的裂变uranium-235 in nuclear reactors. Most of the reactors producing the vast majority of the world's supply of99mTc are quite old now, and frequently shut down for extended periods for repairs, threatening the availability of this vital medical commodity. A worldwide shortage of99mTc occurred in 2010 when two of the99Mo production reactors were offline at the same time, prompting research into alternative methods of99Mo/99mTc production.

One of the most promising alternatives is the use of a linear particle accelerator (or "linac"), instead of nuclear reactors. A linac speeds up charged subatomic particles to a very high velocity along a straight line, as opposed to acceleration around a loop (hence "linear"). The99Mo is produced by irradiating molybdenum trioxide with photons from the linac electron beams, and the99mTc extracted from the decaying99Mo by a technetium-99m generator, sometimes called a "moly cow" by its operators.

What makes this alternative so attractive compared to reactors is that the relatively compact linacs are already widely used in hospitals for radiation treatment for cancer patients.

A challenge this option has faced, however, is that for the99mTc to be usable as a medical tracer, the element must have a high radioactive concentration (RAC -- the amount of radioactivity per volume), and the99Mo precursor produced with linacs has a much lower level of "specific activity" (emissions per molybdenum mass) than that produced as a result of nuclear fission. The99Mo can result in the99mTc having impractically low RAC if the99mTc is extracted using aluminum oxide (alumina) as a filter in the moly cow machine.

To solve this problem, the University of Tokyo researchers replaced the alumina with activated carbon (sometimes called activated charcoal, or just AC), a type of carbon that has been specially processed to have lots of tiny pores. These pores profoundly enhance the surface area of the substance, thus also enhancing the places to which atoms can adhere (and thus be extracted). For this reason, activated carbon is widely used in air filters, sewage treatment, decaffeination and gold purification. This attribute also makes it great for concentrating the99mTc and can be used even with99Mo with low specific activity.

"We had previously demonstrated the practicality of this combined linac-AC method to produce medically usable99mTc, but had yet to perform any preclinical or clinical trials to see if in the body, this alternatively produced radioisotope is as effective as its conventionally produced one," said Jaewoong Jang, an assistant professor at the university and lead author of the study. "We had a great concept, but no idea whether it would be what we call 'bioequivalent' -- in essence, work the same way in patients."

So they injected one group of mice with the linac-AC-derived99mTc in the form of pertechnetate (the most basic compound of technetium used in radiopharmaceuticals) and another group of mice with the conventionally produced99mTc. The mice were then dissected to assess the spread ("biodistribution") of the radioisotope in different organs.

The two types of99mTc放射性药物显示出类似的分配n in all organs and tissues examined, and no adverse effects in the mice were observed, suggesting the clinical applicability of linac-AC-derived99mTc radiopharmaceuticals.

The study was preliminary, with the assessment taking place at only one time point after injection of the radioisotope. The researchers now want to perform additional biodistribution studies at different time points to completely confirm the bioequivalence of the two99mTc methods.

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Story Source:

Materialsprovided byUniversity of Tokyo.Note: Content may be edited for style and length.


Journal Reference:

  1. Jaewoong Jang, Yoshitaka Kumakura, Katsuyoshi Tatenuma, Atsuko Nakanishi Ozeki, Youichiro Wada, Nobuyoshi Akimitsu, Akira Tsuguchi, Hidetoshi Kikunaga, Shogo Higaki, Mitsuru Uesaka.A preliminary biodistribution study of [99mTc]sodium pertechnetate prepared from an electron linear accelerator and activated carbon-based 99mTc generator.Nuclear Medicine and Biology, 2022; 110-111: 1 DOI:10.1016/j.nucmedbio.2022.03.002

Cite This Page:

University of Tokyo. "New production method promises to end medical radioisotope shortages." ScienceDaily. ScienceDaily, 21 April 2022. .
University of Tokyo. (2022, April 21). New production method promises to end medical radioisotope shortages.ScienceDaily. Retrieved July 4, 2023 from www.koonmotors.com/releases/2022/04/220421141630.htm
University of Tokyo. "New production method promises to end medical radioisotope shortages." ScienceDaily. www.koonmotors.com/releases/2022/04/220421141630.htm (accessed July 4, 2023).

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