A research team—led by Dennis Mücher, professor at the Institute for Nuclear Physics at the University of Cologne in Germany and former researcher at the University of Guelph and the TRIUMF particle accelerator in Canada, and Cornelia Höhr, deputy director of Life Sciences at TRIUMF—is collaborating with physicists at FRIB to improve to improve the safety and efficiency of heavy-ion therapy in the precision targeting of cancerous tumors. The team has published its results in Physics in Medicine and Biology.
The era of heavy-ion therapy
Since the late 1800s, medical professionals have used X rays to revolutionize medical diagnosis and treatment. While radiation therapy was a game-changing technology in fighting cancer, it has drawbacks like all cancer treatments. Namely, high-energy X rays in the human body have the potential to damage healthy cells they encounter as readily as tumor cells. Doctors and researchers first started experimenting with proton therapy in the 1940s. Researchers found that by accelerating particle beams with nuclei heavier than protons, radiation could more accurately target cancer cells and spare more healthy tissue—provided they could deliver the particle energy payload exactly where the tumor was located.
The era of heavy-ion therapy was born at Lawrence Berkeley National Laboratory’s Bevelac complex in 1982. The method provides a less invasive and more accurate approach to treating cancer. Today, doctors use heavy-ion therapy worldwide in selected facilities to treat cancer whenever doctors see a benefit over conventional radiation therapy.
International collaboration looks to ensure treatment accuracy
Mücher is interested in ensuring precision for these sensitive procedures. Recently, Mücher and Höhr collaborated with Artemis Spyrou, professor of physics at FRIB and in the Michigan State University (MSU) Department of Physics and Astronomy, and Thomas Baumann, staff physicist at FRIB, to complete a proof-of-principle experiment to improve range verification (RV) for high-energy beams used in heavy-ion therapy. Eva Kasanda, then-PhD student at the University of Guelph and current postdoctoral researcher at the University of Bern in Switzerland, was also a member of the research team.
Mücher said when a patient has a tumor near an area like the brain stem, they can neither get surgery nor receive traditional radiation therapy that might damage such a sensitive body part. Heavy ions stop completely in tissue and exert most of their energy to kill cancerous cells at the end of their range. Such a tenuous situation requires that doctors be confident they deliver radiation precisely. Further, there is no part of the ion beam exiting the patient during treatment, meaning that monitoring the interaction of the beam with the patient is not possible with conventional techniques.
“The human body is complex. There are different tissues, bones, air pockets, and it makes it hard to predict what the exact range of a beam is, and where the bulk of the cell kill happens,” Mücher said. “It can also come down to how precise is the patient placed, or how precise is the beam in its position? These all add up to uncertainty. And uncertainty leads to healthy tissue being damaged.”
Mücher and his collaborators used particle accelerators to identify materials for accurate markers to track RV for particle beams. The Canadian New Frontiers for Research Fund supported the international collaboration. The team focused on improving the accuracy of cancer treatments, leading to more cancer cell kill and to more spared healthy tissue, resulting in a better treatment outcome.
Experiment and theory collide to improve hadron tumor markers
While medical professionals must calibrate a beam’s range down to the millimeter scale, it is difficult to measure the beam’s exact position within the human body. Mücher and his collaborators tested a series of candidate metals that could serve as hadron tumor markers. Like other fiducial markers used in medical procedures, doctors implant tiny pieces of material—most often a metal—to align a beam to a patient. In this case, researchers target the marker in RV experiments and measure gamma radiation signals coming from it.
To improve tumor markers for this therapy, the researchers sought materials that could reliably provide clear gamma-ray signatures in a timely fashion. Spyrou situated the team’s experiment within the larger effort to improve markers for heavy-ion therapy. “We have to characterize these systems before we can run experiments, or start testing a method,” she said. “We start with simulations before our experiments, so we know what gamma rays to expect, but running the experiment helps us truly understand how the whole process works.”
At FRIB, the researchers evaluated a series of materials doctors could use as more effective hadron tumor markers. They needed to identify metals that were easily available, non-toxic, and do not already exist in the body, among other criteria. Using a high-powered beam of oxygen-16, the team evaluated three materials in its investigation and pared down its candidate list to a silver isotope, silver-107, as material for further evaluation.
While the team’s experiment serves as an excellent proof of concept, the researchers need higher energy beams to run experiments that would be like beams used in heavy-ion therapy. The team looks forward to the upcoming upgrade to FRIB, FRIB400, which will enhance FRIB’s capabilities.
“This is exactly what we need regarding energy,” Mücher said. “Having access to this facility enables researchers to perform the experiments needed to improve heavy-ion therapy even further.”
Eric Gedenk is a freelance science writer.
Michigan State University operates the Facility for Rare Isotope Beams (FRIB) as a user facility for the U.S. Department of Energy Office of Science (DOE-SC), supporting the mission of the DOE-SC Office of Nuclear Physics. Hosting what is designed to be the most powerful heavy-ion accelerator, FRIB enables scientists to make discoveries about the properties of rare isotopes in order to better understand the physics of nuclei, nuclear astrophysics, fundamental interactions, and applications for society, including in medicine, homeland security, and industry.
The U.S. Department of Energy Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of today’s most pressing challenges. For more information, visit energy.gov/science.