One of the most common ways to  treat cancer is with radiation.

But depending on the type of cancer, there are different kinds  of radiation you can use, and different ways to get it where it needs to go. For example, some medicines can deliver the radiation  directly into the cancer cells, which avoids damaging the surrounding tissue.

That sounds great! Why aren’t we doing that for everyone? Well, one problem is that  many of the radiation sources those medicines use are super rare.

But scientists are working  on a variety of solutions. And one of the solution is  digging up old nuclear waste. [intro music] All radiation is, really, is  energy that’s given off by matter. It can take the form of waves or particles... or if you want to get pedantic  with some quantum physics, waves that are also particles.

Everyday things like visible light, heat, and radio waves are all types of radiation. But for cancer treatments, we need something that packs a bigger punch, like X-rays, gamma rays, or very fast subatomic particles. Sometimes, we get that high-energy  radiation from big, unstable atoms.

I’ll be getting to some important examples later. Atoms of the same element can  come in different variants, or isotopes, depending on how many neutrons are in the nucleus. And many isotopes of particularly large  atoms just don’t like to exist as-is.

They can become more stable by emitting radiation and transforming into a different isotope, or sometimes into a different element entirely. It’s basically the closest thing  we have to real-life alchemy. To kill cancer cells, the radiation needs to have  enough energy to knock electrons off of a different atom or molecule… say, a molecule of DNA.

When that happens, the bonds holding  that molecule together can break. So over time, radiation therapy  breaks down the DNA of cancer cells. And when the DNA gets damaged,  the cancer cells sometimes can't repair themselves and they die Most people who get radiation  treatment for their cancer get a version called external radiotherapy.

This uses a machine outside the patient’s body to direct radiation toward the cancer cells. That radiation usually takes the form of X-rays, but it might use particles  like protons or electrons, depending on the type of  cancer and where it’s located. I just got the x-rays.

External radiotherapy has been a treatment option since shortly after the discovery of X-rays, way back in 1895. But being, you know, external, the radiation usually has to  pass through some healthy cells to reach the cancer. Those healthy cells could  get damaged along the way.

To get around that issue, researchers in the early 20th century came  up with a form of internal radiotherapy to get the radiation directly to the cancer. Initially, patients would get a tiny dose of  radium embedded directly into their cancer. But it turns out, radium comes with  a whole host of safety concerns.

Just ask Marie Curie. Thanks to nuclear research  conducted in the mid-20th century, scientists could swap radium out  for cheaper, safer alternatives, like cobalt-60, iodine-125, and a  couple different cesium isotopes. But more recently, scientists have found ways to stick radioactive atoms to other molecules that bind to specific sites on cancer cells.

This kind of treatment takes  advantage of the biological pathways of both the radioactive element  and the molecule it’s stuck to, called a ligand. The ligand has just the right  structure to ferry the radiation to the appropriate site in the body. Different ligands and radioactive atoms  work for different types of cancers.

For example, iodine-131 works  well for thyroid cancers, because the thyroid naturally takes up iodine. And a cancer drug called Lutathera uses  a ligand that binds to certain receptors that are common on some cancers in the G. I. tract. t hose receptors aren’t very  common on noncancerous cells, so the drug naturally targets the cancer.

Lutathera and a prostate  cancer drug called Pluvicto both use lutetium-177 as  their radioactive isotope. Its half-life… or, the time it takes for  half of its atoms to decay… is roughly one week. That’s long enough that it  can be transported to patients without losing too much of its potency.

But it’s also short enough that the  patient won’t stay radioactive for too long once they take the medicine. Since lutetium-177 decays fairly quickly, manufacturers have to prepare it fresh. And there are two ways they can do  that: either take a lump of lutetium-176 and bombard it with neutrons.

Or start with ytterbium-176  and hit that with neutrons to make a bunch of ytterbium-177, then wait for it to decay to lutetium-177. Lutetium-177 itself decays via  a process called beta decay. One neutron turns into a  proton, creating hafnium-177, as well as an electron and antineutrino.

Since the proton stays in the nucleus, and antineutrinos don’t like  to interact with anything, the only thing that’s contributing to  the cancer treatment is the electron. Now, beta decay works just fine for cancer drugs. We’ve been using them for decades.

But a new form of radiotherapy could deliver heavy-hitting, targeted  radiation right where it counts. Some radioisotopes decay by emitting  a different kind of radiation known as alpha particles. Alpha particles are made up of  two protons and two neutrons.

These are much larger and heavier  than beta particles, aka electrons. Like, thousands of times heavier. That makes them pack way  more of an energetic punch, and way more effective at  breaking the DNA in cancer cells.

It also makes them easier to block. When it comes to human bodies, alpha particles can pass through  two to five layers of cells before they hit something. Beta particles, meanwhile,  can barrel through 50 layers.

So alpha particles probably won’t work  well for external radiation therapy, but if we can get them right up next to a tumor, they can do a lot of damage to cancer cells and very little to the  surrounding healthy tissues. Scientists are already working  on a new cancer treatment called targeted alpha therapy that  makes use of this powerful radiation. But to find out what element is  involved, you’ll have to wait a moment.

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One promising source of alpha  particles is actinium-225. Actinium actually has more  than thirty different isotopes, and all of them are radioactive. Some stick around for a while  as byproducts of other atoms going through radioactive decay, like uranium and thorium.

Actinium-225 has a half-life of about ten days. So, only a few days longer than lutetium-177. There’s a little more time to ship it to patients, but it’s still short enough that the  patient won’t stay radioactive for too long after taking the medicine.

The actinium atoms themselves are  chemically similar to lutetium. That means researchers might be able to reuse some of  the cancer-targeting ligands we’re already using in  lutetium-based cancer medicines. And when that actinium-225 gets to  its target, it packs a serious wallop.

Like, by the time it decays to a stable isotope, it releases four alpha particles  and two beta particles. In theory, that could offer a  lot of cancer-fighting power. That’s still not happening quite yet, though.

Losing the first alpha particle sometimes  knocks the actinium off of its ligand, separating it from the molecule  meant to deliver it to its target. In that case, any further emissions could wind up happening  somewhere else in the body. But actinium-225 has sparked enough  interest that several clinical trials with the medicine are already underway.

And researchers are starting to think  about how to make enough of the medicine to treat thousands of patients each year. That could be pretty tough. Because right now, we’re making miniscule  amounts of actinium-225 each year.

Like, less than the mass of  a grain of sand globally. Lucky for everybody though, there are  a few ways to make more actinium-225. Remember how I said actinium forms when elements like uranium and  thorium go through radioactive decay?

Turns out, we can make use of that. In fact, we have a whole bunch  of radioactive nuclear waste that’s been slowly decaying for the  better part of the last century. Thorium-229 is an old waste product  left over from nuclear research in the mid-20th century.

And over time, it decays into actinium-225. First, it releases an alpha  particle to become radium-225. Then that radium goes through  beta decay to become actinium-225.

Thorium-229 itself is a  decay product of uranium-233, which is a human-made form of the  element that doesn’t occur naturally. Scientists tested it as a  nuclear fuel source for a while, but eventually they stopped using it. The process of making uranium-233  also produces uranium-232, which emits harmful gamma radiation.

And no one wanted to spend any more  time around that than they had to. We have a bunch of leftover  uranium-233 from those experiments. It’s been slowly decaying at places like  Oak Ridge National Lab in Tennessee, and people are now harvesting thorium-229 from that waste and sending it out  to drug manufacturers and labs working to create those cancer medicines.

This nuclear waste could provide  a steady stream of actinium for many, many years to come. But just waiting around for it to decay isn’t going to give us enough actinium-225 to make the amount of medicine we’d need if targeted alpha therapy goes mainstream. See, uranium-233’s half-life  is almost 160,000 years.

And thorium-229’s half-life  is another 7,300 years. So even though we have a lot  of material to start with, we’re not getting a ton of actinium-225 out of it. The good news is that we can supplement  that steady drip with actinium-225 from another kind of radioactive waste: radium-226.

Blasting radium-226 with high-energy photons can kick a neutron out of the  nucleus and form radium-225. That radium-225 then goes through  beta decay to give us actinium-225. There’s still a bunch of old radium-226 kicking around from old cancer treatments.

It’s left over from early internal radiotherapy, when doctors would implant tiny bits  of radium into cancerous tumors. Now, turning that radium into usable actinium-225 requires equipment to both  create those high-energy photons and hold the material while it decays. And those facilities can  be pretty hard to come by.

But there are plans to get radium waste to  people who do have the necessary equipment. The International Atomic Energy Agency  actually runs an international program that helps recycle old radium waste. And finally, a few places  with specialized equipment are even shooting protons at thorium-232.

The impact can kick off a few protons  and neutrons and form actinium-225. But it also forms a bunch of  other atoms and isotopes t hat would need to be separated out before  you could use that actinium in medicine. Even though none of the  ways to source actinium-225 are particularly easy or convenient, worldwide production is still ramping up.

As of 2026, several drug  manufacturers and research facilities have announced plans to increase  their capacity to make the isotope. But actinium-225 isn’t the only  alpha-particle-emitting isotope that researchers are investigating  for cancer treatment. There are a handful of other options that  could take off in the next few years.

Some scientists are looking into bismuth-213, which forms when actinium-225 decays. Others are researching lead-212. Both isotopes have short half-lives, which could limit a patient’s  radiation exposure over time.

And some researchers are  working with astatine-211. The cancer-targeting molecules  that attach to astatine-211 a re relatively small, which means they might be able to  pass through the blood-brain barrier and help treat brain cancers, which is very tricky. Targeted alpha therapy is  still in the early stages.

But if it’s successful, it could  mean that radioactive waste becomes a new tool in our cancer-fighting arsenal. We always knew it would be useful some day! [ outro music ]