Fighting Cancer with Muons

Yes, you read that right: Muon Radiation Therapy. The (almost unpronounceable) word “muons” is derived from the Greek letter μ and it might quite sound exotic — and, in a sense, it is! These fleeting elementary particles have a mean lifetime of about 2.2 microseconds, yet thanks to Einstein’s theory of special relativity, they can travel far greater distances than expected (when moving at an appropriate speed).

Muons are produced naturally in the interaction of cosmic rays with the atmosphere, contributing to the radiation dose we receive at ground level. They’re also created in dedicated facilities called muon colliders (but I like more to say "muon factories"), or as by-products of nuclear reactions in installations designed for entirely different purposes.

Let's talk Muon Radiation Therapy

Don't let me wander too far from the topic (as much as muons would love to escape). Let me guide you into the key facts of Muon Radiation Therapy.

The Facts

First proposed for radiotherapy by N. V. Mokhov and A. Van Ginneken at Fermilab in 1999, muons showed promise as a novel treatment modality. Here are the potential advantages of muons in treating cancer:

• Lower entrance dose: Muons deposit less energy (than other types of radiation) in the tissues they pass through on their way to the tumor, reducing damage to healthy tissues near the surface.
• Larger lateral dose profiles: Perfect for larger or irregularly shaped lesions, muons can be imagined delivering a more uniform dose across the target area.
• Adaptability: With some modifications, existing proton therapy machines could theoretically be retrofitted to produce muons. To make them able to deliver muons usable for therapy? Well, that's all another story.

The early simulations by Mokhov and Van Ginneken, conducted with the MARS Monte Carlo code, demonstrated that cooled muon beams could rival protons in their ability to target tumors. Even better, they appeared to distribute doses more uniformly across the treatment area. Super cool, right?

So why didn’t the idea fly like a muon to its target?

Much like muons themselves, which vanish in microseconds, the idea of muon therapy didn’t stick around long — though sporadic research papers on the subject continue to surface decades later. (Relativity joke: this is possible because visionary ideas are like atmospheric muons: reaching far, even though everyone thought they would die earlier!)

So, what are the challenges holding muon therapy back?

?? Key challenges

1. Production: Generating high-energy muon beams requires complex and costly infrastructure, often as a by-product of other high-energy physics facilities.
2. Short half-life: Muons of useful energies decay quickly, making it difficult to ensure reliable beam delivery to the patient.
3. Cost and complexity: Compared to well-established methods like linacs, brachytherapy, or even proton therapy, muon therapy is prohibitively expensive and technologically demanding.
4. Scalability: While existing modalities are increasingly accessible and scalable, muon therapy remains more of a niche concept.

The future: can we dream of muon therapy?

Exotic ideas like muon therapy often face an uphill battle against practicality. In a world with a growing demand for cancer care, solutions that are cost-effective and scalable — like in-hospital linacs, brachytherapy, and gamma knife systems — remain unchallengeable. The advanced development of these technologies ensures their place as the mainstays of modern cancer treatment. Just imagine that over 70% of population in Africa did not have access to radiotherapy according to the 2022 "Cancer Care for All" report by the IAEA.

However, dreaming of a muon therapy center isn’t out of the question. Perhaps one day, with technological breakthroughs and a bold leap of imagination, we’ll see muons playing a role in the fight against cancer.

Why scalability is important. In one picture.

A personal connection

As you know, most of my stories have a personal connection. Mokhov’s MARS Monte Carlo code was the first simulation tool used at the European Spallation Source (ESS) to design the radiation shielding for its 2 GeV proton linear accelerator.

And one of my very first tasks at ESS was to transition from MARS to MCNP. Why? Because MCNP has the capability to simulate neutron production near threshold energy, which is necessary when looking at the normal-conducting section of the accelerator — something MARS could not do.

But there’s more: Mokhov’s 1999 paper references the work of Stepan Mashnik, one of the key developers of MCNP and someone who became a mentor during the early stages of my career. At the time when Mashnik published the referenced work, he was still based in Dubna, the Soviet Union’s heart of nuclear research.

Dubna

Dubna deserves its own article (I will write it, I promise), one of those places not many have visited. I was fortunate enough to be invited there twice, back in the days when access to Russia and its nuclear research facilities was still possible. Oh, yes, and Mashnik’s influence didn’t end with his work in Dubna and later with his fundamental contribution to developing MCNP at the Los Alamos National Laboratory; Stepan played a role also in recommending me for my position at ESS, for which I will be always grateful!

Read more

• The original 1999 article by Mokhov and Van Ginneken: https://digital.library.unt.edu/ark:/67531/metadc696104/m2/1/high_res_d/5609.pdf
• Please mind the gap—about equity and access to care in oncology: Please mind the gap—about equity and access to care in oncology - PMC
• The Compact Muon Solenoid (CMS) experiment at CERN: The cms detector | CMS Experiment
• Take some time to read and honour the memory of Stepan Mashnik: https://www.dhirubhai.net/pulse/remembering-stepan-mashnik-riccardo-bevilacqua/?trackingId=KlRjCn2VTRyrrNObyg%2BOPw%3D%3D

About me

I’m passionate about radiation and radiation safety, and I lead these efforts at a top MedTech company. My experience includes working with the European Commission and international physics laboratories, where I developed my expertise in nuclear physics (without causing any explosions!). With a PhD in applied nuclear physics, I’ve published research in peer-reviewed journals and enjoy crafting content that makes complex topics in science, safety, and security accessible and engaging—because everyone loves a good science story!

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