Flushing Doesn’t Mean It’s Gone. Growing alpha therapies demand wastewater protection.

Targeted alpha therapy is rapidly emerging as one of the most exciting developments in nuclear medicine. Actinium-225 (Ac-225) offers something remarkable: highly potent alpha radiation delivered selectively to cancer cells. But its rise also introduces a question that deserves more attention.

What happens after the patient goes to the toilet?

A different kind of radionuclide

Ac-225 is not simply another therapeutic radionuclide.

It has a half-life of approximately ten days and decays through a chain of daughter radionuclides before eventually reaching stable bismuth. Several steps in that chain emit alpha particles.

That is precisely what makes Ac-225 therapeutically attractive. But it also makes its behaviour after administration more complex.

The energy released during alpha decay can cause daughter radionuclides to break free from the molecule carrying the original Ac-225. These so-called recoiling daughters can subsequently behave differently from the parent radionuclide. Recent clinical research has confirmed that daughter-specific pharmacokinetics are relevant and that both Ac-225 and daughter activity can be detected in patients’ urine.

There is another consideration. Depending on how Ac-225 is produced, small quantities of long-lived Ac-227 may be present as a radionuclidic impurity. Unlike Ac-225, Ac-227 has a half-life of almost 22 years.

As alpha therapies scale, understanding what leaves the patient therefore becomes increasingly relevant.

The patient may leave. The radionuclides do not disappear.

Part of the administered radioactivity leaves the body through excreta. Once flushed, it has not disappeared. It has simply moved from a controlled clinical environment into the wastewater system.

This raises an interesting regulatory contrast.

In the United States, NRC regulations specifically exempt excreta from patients undergoing diagnosis or therapy with radioactive material from the normal limitations governing radioactive releases into sanitary sewerage.

That regulatory framework was not designed around the scale of targeted alpha therapies now being developed. And a municipal wastewater treatment plant is not a nuclear-waste treatment facility.

Once radionuclides enter the sewer, controlling them becomes fundamentally more difficult. They may interact with solids and sludge or continue through the water chain while radioactive decay continues.

Flushing does not remove radioactivity. It changes where the radioactivity is.

Alpha therapy needs an environmental strategy.

None of this is an argument against targeted alpha therapy. Quite the opposite.

These therapies have enormous potential for patients. The challenge is to make sure that the infrastructure surrounding them develops at the same pace as the medicines themselves.

And that brings us back to the most controllable point in the chain: the hospital.

When patients first excrete radionuclides, the wastewater volume is still small, the origin is known and the activity has not yet been dispersed through kilometres of sewer infrastructure.

Hospitals can manage this in different ways. Conventional decay tanks collect radioactive wastewater and retain it while activity decays. Zereau’s source-based filtration offers another approach: capturing radionuclides directly from patient excreta before they enter the wider wastewater system.

Zereau has been developing and implementing this source-based approach for radioligand therapies in multiple European hospitals. It requires far less water to be managed and can avoid the extensive infrastructure associated with large decay-tank installations. On top of this, alpha therapies can be easily shielded, simple handling procedures guaranteed.

For Ac-225 and the next generation of alpha therapies, this may become increasingly relevant. Because innovation in nuclear medicine should not stop at the patient.

As therapies become more powerful, the way we manage what leaves the patient should evolve with them.