Mixed beam measurement method could help make ion cancer therapy more precise

by Vienna University of Technology

edited by Gaby Clark, reviewed by Robert Egan

Gaby Clark

Scientific Editor

Meet our editorial team
Behind our editorial process

Robert Egan

Senior Editor

Meet our editorial team
Behind our editorial process Editors' notes

This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility:

fact-checked

trusted source

proofread

The GIST Add to Preferred Sources

In ion beam therapy, atomic nuclei are accelerated to high energies in a particle accelerator, for example, a synchrotron, and precisely directed at a tumor. There, they damage cancer cells and destroy tumor tissue. This technique is now used at several specialized medical facilities around the world, including MedAustron in Wiener Neustadt, Austria.

A new approach currently being investigated involves so-called "mixed beams," which consist of two different ion species: Carbon nuclei destroy the tumor cells, while helium nuclei simultaneously help monitor the patient's anatomy during irradiation. To make this possible, however, the precise ratio of carbon to helium in the beam must be known.

But how can an ion beam be measured while it is being used for treatment? TU Wien and MedAustron have now found a solution—an important step on the path toward cancer treatment using mixed ion beams. The paper is published in the journal Physical Review Accelerators and Beams.

Irradiating as little as possible

Despite the high precision of ion beam therapy, uncertainties remain. Organ motion, for example, can shift the location at which the beam deposits most of its energy—also called the "range" of the beam—by a few millimeters. To ensure that the entire tumor is treated despite these uncertainties, a small safety margin around the tumor is irradiated as well. The smaller this margin can be made, the more precise the therapy becomes and the better sensitive organs nearby can be spared.

To minimize side effects, it would therefore be ideal to monitor the range of the beam as precisely as possible during treatment. This is where the concept of mixed beams comes in: Carbon and helium ions are combined in a single beam. All electrons are removed, leaving carbon nuclei with exactly three times the electric charge of helium nuclei and almost exactly three times their mass.

"Because their charge-to-mass ratios are almost identical, the two ion species also follow almost exactly the same trajectory in the particle accelerator, allowing us to accelerate them simultaneously to high energies and direct them toward the patient," explains Elisabeth Renner.

In tissue, however, a crucial difference emerges: Helium ions can travel much farther through the body—approximately three times as far. A mixed beam can therefore be sent through the body in such a way that the carbon ions are used to destroy the tumor tissue, while the helium ions pass through the body.

The emerging helium ions can then be measured. From the residual energy of the helium ions, one can reconstruct how far the carbon ions have actually penetrated into the tissue and whether the irradiation is proceeding as planned. This could allow researchers to reduce the safety margins and hence spare even more healthy tissue, particularly in the case of tumors located very close to sensitive organs.

"For this method to work, however, we need to know and control very precisely how large the carbon and helium fractions in the beam are," says Renner. And that is a major challenge: Either the beam is measured, or it is used for irradiation. Doing both at the same time is difficult.

How to measure a beam without stopping it

The research team at TU Wien and MedAustron has now found a solution. Strictly speaking, a carbon nucleus does not have exactly three times the mass of a helium nucleus, but about 0.065% less. This tiny difference means that carbon and helium are forced onto slightly different trajectories inside the particle accelerator.

"In the accelerator, we continuously monitor whether the center of the particle beam remains on its intended trajectory," explains Renner. "If it deviates, the accelerator's radio frequency is adjusted ever so slightly. Because helium and carbon nuclei behave slightly differently due to their tiny mass difference, the required frequency correction depends on the mixing ratio."

By precisely monitoring the frequency needed to stabilize the beam, the carbon-to-helium ratio can therefore be determined.

This was calculated at TU Wien and tested in collaboration with MedAustron—and the results show excellent agreement.

"We were able to demonstrate that this method allows us to determine the helium and carbon fractions in the beam without affecting or interrupting the beam itself. This means that during experiments, and possibly also during treatments in the future, we can check whether the helium fraction in the beam corresponds to the desired value. Only if that is the case should the beam be cleared for irradiation."

The results have now been published and are already attracting international attention: On Oct. 8 and 9, 2026, researchers from a range of international particle accelerator facilities came to TU Wien for the "1st Workshop on Mixed Ion Beam Delivery" to discuss current developments and challenges in the delivery and use of mixed ion beams.

More information

Elisabeth Renner et al., Noninvasive ion fraction quantification of dual-species beams in synchrotrons, Physical Review Accelerators and Beams (2026). DOI: 10.1103/5bxb-lp5d

Clinical categories

Oncology Provided by Vienna University of Technology Who's behind this story?

Gaby Clark

MA in English, copy editor since 2021 with experience in higher education and health content. Dedicated to trustworthy science news. Full profile →

Robert Egan

Bachelor's in mathematical biology, Master's in creative writing. Well-traveled with unique perspectives on science and language. Full profile →

Citation: Mixed beam measurement method could help make ion cancer therapy more precise (2026, October 14) retrieved 14 October 2026 from https://medicalxpress.com/news/2026-10-method-ion-cancer-therapy-precise.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.