Turning Radioactive Waste Into Cancer Treatment: How Targeted Radiation Could Use Old Nuclear Material

Hank Green begins by noting that one of the most common ways to treat cancer is with radiation. He explains that, depending on the type of cancer, different kinds of radiation can be used, and there are different ways to deliver it to where it needs to go.

He describes one approach in which some medicines can deliver the radiation directly into the cancer cells, which avoids damaging the surrounding tissue. He adds that this sounds great, but the main problem is that many of the radiation sources those medicines use are very rare. Scientists are working on a variety of solutions, one of which involves digging up old nuclear waste.

Green explains that radiation is energy given off by matter, and it can take the form of waves or particles. Everyday things such as visible light, heat, and radio waves are all types of radiation, but cancer treatments need something with more energy, such as X-rays, gamma rays, or very fast subatomic particles. Some of this high-energy radiation comes from large, unstable atoms.

Atoms of the same element can exist as different isotopes depending on how many neutrons are in the nucleus. Many isotopes of particularly large atoms do not stay stable and become more stable by emitting radiation and transforming into a different isotope or sometimes a different element. Green calls this basically the closest thing we have to real-life alchemy.

To kill cancer cells, radiation needs enough energy to knock electrons off another atom or molecule, such as a molecule of DNA. When that happens, the bonds holding the molecule together can break, so over time radiation therapy breaks down the DNA of cancer cells. When the DNA is damaged, cancer cells sometimes cannot repair themselves and they die.

Most people receiving radiation for cancer get external radiotherapy, which uses a machine outside the body to direct radiation toward cancer cells. That radiation usually takes the form of X-rays, but it may use protons or electrons depending on the cancer type and location. External radiotherapy has been an option since shortly after the discovery of X-rays in 1895.

Because external radiation usually has to pass through some healthy cells to reach the cancer, those cells could be damaged along the way. To get around this, researchers in the early 20th century developed a form of internal radiotherapy. Initially, patients would receive a tiny dose of radium embedded directly into their cancer. Green notes that radium comes with a whole host of safety concerns, and says to just ask Marie Curie.

Thanks to nuclear research in the mid-20th century, scientists could replace radium with cheaper, safer alternatives such as cobalt-60, iodine-125, and a couple of cesium isotopes. More recently, scientists have found ways to attach radioactive atoms to other molecules that bind to specific sites on cancer cells. Such a molecule is called a ligand, and this approach uses the biological pathways of both the radioactive element and the molecule it is attached to.

Different ligands and radioactive atoms suit different cancers. Iodine-131 works well for thyroid cancers because the thyroid naturally takes up iodine. The cancer drug Lutathera uses a ligand that binds to certain receptors common on some cancers of the gastrointestinal tract; those receptors are not very common on noncancerous cells, so the drug naturally targets the cancer. Lutathera and the prostate cancer drug Pluvicto both use lutetium-177. Its half-life, the time it takes for half of its atoms to decay, is roughly one week. That is long enough to transport it to patients without losing much potency, but short enough that patients do not stay radioactive for too long after taking the medicine.

Because lutetium-177 decays fairly quickly, manufacturers have to prepare it fresh. Green describes two ways to do this: either bombard a lump of lutetium-176 with neutrons, or start with ytterbium-176, bombard it with neutrons to make ytterbium-177, and then wait for that to decay into lutetium-177.

Lutetium-177 itself decays through beta decay. One neutron turns into a proton, creating hafnium-177, along with an electron and an antineutrino. Because the proton stays in the nucleus and antineutrinos do not interact with anything, Green says the only part contributing to the cancer treatment is the electron. He adds that beta decay works fine for cancer drugs and has been used for decades.

A newer form of radiotherapy could deliver heavy-hitting, targeted radiation where it counts. Some radioisotopes decay by emitting alpha particles, which are made up of two protons and two neutrons. Green says these are much larger and heavier than beta particles, which are electrons, and in fact thousands of times heavier. That makes them pack far more energy and makes them more effective at breaking the DNA of cancer cells.

Alpha particles are also easier to block. In human bodies, they can pass through only two to five layers of cells before hitting something, while beta particles can barrel through 50 layers. Green concludes that alpha particles probably will not work well for external radiation therapy, but if they can be placed right next to a tumor, they can do a lot of damage to cancer cells and very little to surrounding healthy tissue. Scientists are working on a treatment called targeted alpha therapy that makes use of this radiation.

Green describes actinium-225 as one promising source of alpha particles. Actinium has more than thirty isotopes, all of which are radioactive. Some form as byproducts of other atoms going through radioactive decay, such as uranium and thorium. Actinium-225 has a half-life of about ten days, only a few days longer than lutetium-177, which gives somewhat more time to ship it to patients while still keeping patients from staying radioactive for too long.

The actinium atoms are chemically similar to lutetium, so researchers may be able to reuse some of the cancer-targeting ligands already used in lutetium-based medicines. When actinium-225 reaches its target, it releases four alpha particles and two beta particles by the time it decays to a stable isotope. Green says that in theory this could offer a lot of cancer-fighting power.

Green explains that the idea is not yet fully realized. Losing the first alpha particle sometimes knocks the actinium off its ligand, separating it from the molecule meant to deliver it to its target. In that case, any further emissions could happen somewhere else in the body.

Even so, actinium-225 has sparked enough interest that several clinical trials are already underway. Researchers are starting to think about how to make enough of the medicine to treat thousands of patients each year, which could be difficult. Green notes that right now only minuscule amounts of actinium-225 are made each year, less than the mass of a grain of sand globally.

Since actinium forms when elements such as uranium and thorium decay, Green says that process can be used. He notes that there is a whole bunch of radioactive nuclear waste that has been slowly decaying for the better part of the last century. Thorium-229 is an old waste product left over from mid-20th-century nuclear research, and over time it decays into actinium-225: first it releases an alpha particle to become radium-225, and then that radium goes through beta decay to become actinium-225.

Thorium-229 is itself a decay product of uranium-233, a human-made form of the element that does not occur naturally. Scientists tested uranium-233 as a nuclear fuel source for a while before stopping. Making uranium-233 also produced uranium-232, which emits harmful gamma radiation. Leftover uranium-233 from those experiments has been decaying at places such as Oak Ridge National Lab in Tennessee, and thorium-229 is now being harvested from that waste and sent to drug manufacturers and labs making cancer medicines. Green says this could provide a steady stream of actinium for many years to come.

Green cautions that just waiting for the waste to decay will not give enough actinium-225 for the medicine that would be needed if targeted alpha therapy goes mainstream. Uranium-233 has a half-life of almost 160,000 years, and thorium-229 has a half-life of another 7,300 years. So even with a lot of starting material, little actinium-225 comes out of it.

Green says the steady supply can be supplemented by another kind of radioactive waste, radium-226. Blasting radium-226 with high-energy photons can knock a neutron out of the nucleus and form radium-225, which then goes through beta decay to give actinium-225. Radium-226 is left over from early internal radiotherapy, when doctors implanted tiny bits of radium into tumors. Turning it into usable actinium-225 requires equipment to create the high-energy photons and to hold the material while it decays, and such facilities can be hard to find. The International Atomic Energy Agency runs an international program to help recycle old radium waste. A few places with specialized equipment are also shooting protons at thorium-232, which can form actinium-225, but it also forms other atoms and isotopes that must be separated out before use in medicine.

Green notes that although 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. Actinium-225 is not the only alpha-particle-emitting isotope researchers are investigating for cancer treatment.

Some scientists are looking into bismuth-213, which forms when actinium-225 decays, and others are researching lead-212. Both have short half-lives, which could limit a patient's radiation exposure over time. Some researchers are working with astatine-211. The cancer-targeting molecules that attach to astatine-211 are relatively small, which may let them pass through the blood-brain barrier and help treat brain cancers, a very tricky task. Green concludes that targeted alpha therapy is still in the early stages, but if successful, radioactive waste could become a new tool in the cancer-fighting arsenal.