Submitted by Gwaiian t3_10rz10c in askscience
I felt this was a science question, but now it seems more like a logistics question. But I just don't understand how the Tc-99m can be available in this Canadian hospital unless large amounts are harvested from US facilities and shipped here constantly as they break down so quickly.
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Good question. Radiopharmaceuticals like this one is produced at the hospital by use of a “cold kit” which is then tested and released for use shortly before the patient is injected and scanned. Page 3-5 in this https://www-pub.iaea.org/mtcd/publications/pdf/trs466_web.pdf explains it well.
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Pharmacist who used to work in a nuclear pharmacy - they don’t keep it in stock! Doses are custom made for each patient every day at a (usually) offsite nuclear pharmacy, and then a van delivers them to the imaging center so they can be injected at precisely the right time to deliver the prescribed dose of radiation for the imaging! Logistically, it doesn’t make sense for most medical centers to have their own nuclear pharmacy, so one location will service large metropolitan areas. Happy to answer any addition questions!
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Hello fellow Canadian! Mo-99 is NOT made from nuclear weapons waste. It is deliberately made in reactors or accelerators specifically as a medical product. Canada used to be one of the largest suppliers of Mo-99 in the world, making it in the NRU research reactor in Chalk River. That reactor shutdown in 2018. The Darlington CANDU plant is now equipped to make Mo-99, in addition to lots of carbon free power.
https://world-nuclear-news.org/Articles/Darlington-ready-to-produce-medical-radioisotope
As others have said, it's not "stocked" on a shelf like many medications. It is custom made to order and patients are scheduled.
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Radiochemist here. Tc-99m is a so-called generator produced isotope. It is a decay product of Mo-99 (half-life 66h) which is produced via fission of U-235 (around 6% of the fission products is Mo-99). Mo-99 is separated from U-235 and afterwards bound to a stationary/solid phase. There it decays constantly to Tc-99m. Due to the different chemical nature of Mo and Tc you can easily elute the Tc-99m for preparation of the radiopharmaceutical. Hospitals have these Mo-99/Tc-99m generators on site and elute them every day. As the Mo-99 decays these generators needs to be replaced after 1-2 weeks. After elution of the Tc-99m the radiopharmaceutical is then usually prepared via a kit. It is like a pre-made mix where you just need to add the Tc-99m, shake for a minute and it's ready to use for patients.
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Most hospitals definitely do not have their own radioisotope generator.
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The University of British Columbia uses a long distance pneumatic tube. The video doesn't mention Technetium, but they use it for C-11 with a half life of 20 minutes.
https://www.youtube.com/watch?v=eMTZvA8iFgI
That's unusual; road transport is more common. The production, from a particle accelerator, is quite common for certain isotopes though.
A 'nuclear pharmacy' is an amazingly sounding concept.
I mean, its obvious what it is, but still lovely to let the imagination to run about.
It's an application area if you graduate with a Phd in nuclear physics. I worked with several physicists when I was in medical imaging. They dealt with dosimetry in radiation therapy.
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Isotope generators at each facility are common in Canada https://www.nrcan.gc.ca/energy/uranium-nuclear/7799 but it seems to be shifting to a more centralised cyclotron supply chain https://www.triumf.ca/headlines/cyclotron-produced-technetium-99m-approved-health-canada
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Wow, thank you. Apparently my ten minute deep dive into nuclear medical isotopes didn't give me all the right info to make assumptions. And as a news junkie I do recall the Chalk River shutdown. Thanks!
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How are famuly members of those patients protected from exposure? It seems like a sneeze or a cough could release radioactive material into the air of the patient’s home.
What happens if traffic is awful one day and people are an hour late? Is the scheduled injection ruined?
it has six hours half-life. In 24 hours, only 6% remain and in 48 hours 0,4%
and that's without factoring in its biological halflife. Most of it goes down the toilet.
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I was gonna ask, didn’t DuPont market a technium generator a long time ago for hospitals to use?
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Nuclear physicist here. This guy has the right answer. I can add that these generators are compact in size (though heavy because of radiation shielding) and can be delivered to the hospital with fresh Mo-99 inside. The old generators with depleted Mo-99 are picked up when the new generators are delivered. The extraction of the Tc-99m can be done within the hospital. It actually gets sucked out of the generator with special syringes that have been manufactured with a defined underpressure inside and the first thing to do with a new generator after this sucking process (called elution) is to check it for Mo-99 contamination. Only <1% of Mo-99 is allowed (where I live, ymmv).
If it’s safe to have it injected it in you, it’s safe to be around someone who will cough out maybe 0.001% of what they had injected into them. Especially with such a short half life
You can calculate decay by Nt=No(1/2)^(t/t1/2), where Nt is the number of atoms at time t, No is the original number of atoms, and t1/2 is the half-life. So 1 h later for a 6 h half-life means 89% of the dose is still there.
You would need to ask one of the pharmacists what they do if someone is late. I'm assuming there is a cutoff time.
You're welcome. The Mo-99 at Darlington is specifically in Unit 2, which was just completely refurbished and can operate now for another 30 years. There is also lots of exciting work happening in Chalk River, just not with a research reactor. If medical isotopes interest you, check out the work with Ac-225 in Chalk River as a targeted alpha therapy for cancer treatment.
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Lovely, thank you. I've seen the process in action and noticed there was a specific representative "responsible" for the medicine, but never thought to question the process or logistics vis a vis half life. So neat!
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Who said it's safe? Risk is relative.
Tom Scott has a video talking about something similar. Iirc, he visits the lab that produces radioisotopes for a hospital, mostly focusing on the tube they use to send it down the street super fast.
I don't have a link though :(
I work in pharma and met a guy who does these logistics for a living. It was FASCINATING.
I don't know how you are , but Thank you ☺
I wish they would talk more about potential jobs for different areas of college studies. I always thought for nuclear physics you just work at some power plant.
Not have the medical imaging done seems more risky health wise then some radiation.
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Exactly. But that doesn't mean that the radiation is "safe", which is what I responded to.
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There is a cutoff time. As the 99mTc decays, more and more of it becomes useless. There are several reasons it becomes useless (begins to lose its tag to whatever chemical it’s tagged to, decays and the amount of radiation left is too small to use, oxidizes, etc). There is an expiration time on each dose we receive and there are strict limits to how much and how little radiation we can give a patient depending on the type of scan we are doing. I’m a nuclear medicine tech, so I deal with this stuff all the time.
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Roughly how long is the cutoff time? (E.g. if the courier is late by 1 hour?)
An hour wouldn’t make a difference typically, but each site has their own agreed-on dose ranges. At my sites, I have usually about a 2-3 hour range before my doses would be too low.
So the pharmacy you order from prepares the doses all together and calculates how much radiation will be in each dose at a prescribed time (so if I open a dose calibrated for 2pm at 9am, the dose is WAY too high to give to someone, but if I did give it, it would still work as intended). I’m giving this example in unit doses. Some places will order bulk doses, where they can draw up their own amount of radiation at any given time.
When I order for, let’s say three patients, we will say that each of them are coming in one hour apart from each other. I’ll order 10 mCi of technetium at 9 AM, 10 AM, and 11 AM. Each of my patients come at those times . If a patient is an hour late, the dose will be lower, but it will be usable still. After a certain time you are not giving enough radiation to make good pictures. So if my 9 AM patient comes at noon and I don’t have enough radiation to give them, I would reschedule them so they get better pictures a different day.
The other reason that those does expire is because the tag breaks up on the technetium. So when I do a patient, I’ll order 10 mCi of 99m technetium sestamibi, let’s say. The sestamibi will hold its tag to the technetium for several hours. If the pharmacy makes that dose at 2 AM and ships it out to me calibrated for 9 AM, I can inject the patient with that amount of radiation from probably 8 to 10 a.m. It’s around 5 PM or so, the tag is two broken up to still go to the correct place in the human body. Straight technetium 99m goes to the stomach, the thyroid, kidneys, and other areas of the body. Technetium 99m sestamibi goes to the heart muscle, but also goes to some of those other areas of the body too. So when the sestamibi breaks off, it won’t go to the heart muscle anymore. If I’m trying to get a heart scan on a patient, it doesn’t do me any good to inject something that isn’t going to go to the target organ anymore.
Does that make sense? I feel like I might be more confusing than helpful, but there are several reasons you wouldn’t inject after a specific time, not just that the radiation is decayed.
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Yes, that makes sense, thank you!
I believe that is at UBC. There is a lab that makes the medical isotopes and sends it to the hospital through pneumatic tubes under the ground. Very cool.
[deleted] t1_j6yrgz0 wrote
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