April 28, 2026
Radiation therapy is a cornerstone of treatment for many types of cancer, but it comes with a challenge: not harming the healthy tissue surrounding the tumor. Some parts of the body, such as the gastrointestinal tract, are particularly susceptible to damage from radiation. For example, radiation is often recommended for pancreatic cancer, but the treatment can be tricky because the pancreas is so close to the small intestine, which is very sensitive to radiation. Patients can suffer from nausea, diarrhea, vomiting and abdominal pain, and sometimes even have to stop the treatment.
Proton therapy, an advanced type of radiation treatment, can be used for some cancers when conventional radiation therapy poses a threat to surrounding tissue. While conventional radiation therapy delivers X-rays, or beams of photons, to the tumor and beyond it, proton therapy delivers beams of protons — positively charged atomic particles — that can be stopped at the tumor, with little to no “exit dose” passing through it. The result is less damage to the tissue surrounding the malignancy.
“That is the advantage of using protons over photons — the sparing of normal tissue,” said Subhrajit Saha, PhD, professor of radiation oncology at The University of Kansas Cancer Center.
A recent study published in Advanced Science explains how a new kind of proton therapy may protect healthy tissue even better. This study, conducted by a KU research team led by Saha and in partnership with IBA, a medical technology company, focuses on ultra-high dose-rate proton therapy currently in development across the country. “This study paves the way for delivering powerful, tumor-killing doses with minimal side effects,” said Saha.
Known as Proton FLASH radiotherapy, this new type of proton therapy delivers proton beams to the site of the tumor extremely quickly. Preclinical studies have shown that this accelerated form of treatment maximizes the tissue-sparing effect, while not compromising the therapy’s ability to fight cancer. Yet not much is yet known about how and why FLASH is able to do this.
Saha and his research team set out to learn more. They used a mouse model to study the effect of FLASH on the small intestine, which they focused on because of its proximity to pancreatic and liver tumors and its high susceptibility to radiation injury. “Our first observation is that the ultra-high dose-rate proton radiation is much, much safer,” said Saha. “The sparing of the normal tissue is much, much higher compared to the conventional dose rate, even with proton therapy.”
To understand more about why that is, they looked specifically at the effect on intestinal stem cells. As their previous research had shown, these stem cells are critical for the maintenance and repair of the epithelium, or lining, of the small intestine. What they observed was that FLASH, unlike both conventional proton therapy and typical radiation therapy, spared those stem cells.
The researchers also looked at the intestinal microbiome. This ecosystem of trillions of different bacteria, viruses and other microbes inside the intestines helps rescue dying tissue — including the intestinal epithelium — from any sort of toxicity, including radiation toxicity. They found that these bacteria were also getting spared with the ultra-high dose rate. Moreover, for the mice that were irradiated with FLASH, there were higher levels of two types of bacteria known for their protective effects on intestinal stem cells. “That is very new information,” said Saha. “This is the first evidence of the involvement of the microbiome in the mechanism of FLASH.”
Saha also noted that because FLASH takes less time and is more impactful, it also has the potential to lower cancer treatment costs, while improving the effectiveness of treatment.
“This is a massive milestone in our journey to make radiotherapy more effective, safer and life-changing for cancer patients everywhere,” said Saha.
This article originally appeared on the University of Kansas Medical Center's website.