Splitting Radiation Into Several Sessions Reduced Recurrence of Large Brain Metastases

When cancer spreads to the brain, a large tumor is often removed with surgery. Because cancer cells can be left behind in the space where the tumor was (called the surgical cavity), patients then usually receive stereotactic radiosurgery (SRS): precisely aimed, high-dose radiation to that spot.

For years, that radiation has usually been given in a single session. But a single session has a built-in limit. The larger the area being treated, the more healthy brain tissue is exposed, so doctors often have to lower the dose to keep it safe, and a lower dose may not control the cancer as well.

A new phase 3 trial suggests splitting the radiation into several sessions works better.

What the Trial Tested

The Alliance A071801 trial, led by Dr. Paul D. Brown, a radiation oncologist at Mayo Clinic, was presented Sept. 28, 2026, as a late-breaking abstract at the American Society for Radiation Oncology (ASTRO) Annual Meeting in Boston. It was funded by the National Cancer Institute.

Between 2019 and 2022, the trial enrolled 242 patients with one to four brain metastases, at least one of which was larger than 2 centimeters and had been removed with surgery. Patients were randomly assigned to:

• Single-session SRS, the long-standing approach, or
• Fractionated SRS, with the total dose divided over three to five sessions.

In both groups, doses were tailored to the size of the area being treated. Any brain metastases that had not been removed with surgery were treated on the same schedule the patient was assigned to.

Why Splitting the Dose May Help

Healthy brain cells are better than cancer cells at repairing radiation damage between treatments. Brown said dividing the radiation gives healthy tissue time to recover between doses. That allows doctors to deliver a stronger overall dose to the cavity without raising the risk to the surrounding brain.

What It Found

With a median follow-up of about four years:

• Cancer control at the surgery site: This was the trial's main goal. At one year, 87% of patients in the fractionated group had no recurrence at the surgery site, compared with 81% of those who had a single session. The difference was statistically significant.
• Tumors that weren't removed: In patients with additional brain metastases that were treated with radiation alone, those tumors grew in 4% of the fractionated group and 11% of the single-session group. That difference was not statistically significant, but it pointed in the same direction.
• Survival: People who received fractionated SRS lived a median of 29 months, compared with 20 months with a single session, a 31% lower risk of death. The difference held up after researchers accounted for other factors that affect survival.
• Side effects: Rates were low in both groups, and there was no difference in side effects or complications between the two approaches.

A Survival Finding That Needs More Study

The nine-month survival difference was unexpected. The trial was designed to measure cancer control in the brain, not survival, and researchers said they can't yet explain why fractionation was linked to longer life. Better control of cancer in the brain may play a role, but that will need to be studied further before doctors can say fractionation helps people live longer.

Even so, study co-author Dr. Ayal A. Aizer of Dana-Farber Brigham Cancer Center said "three to five sessions should now be considered a standard postoperative treatment."

What It Means for You

If you're facing surgery for a brain metastasis larger than about 2 centimeters, ask whether the radiation afterward will be given in one session or several. These results give doctors strong evidence to make several sessions the standard.

Fractionated treatment means a few more visits to the radiation center. But based on this trial, it offers better control of the cancer at the surgery site, with no added side effects. If traveling for several appointments is hard, talk with your care team about scheduling, transportation or lodging help.

After treatment, regular brain MRIs are still important. SRS treats only the areas that are targeted, so new metastases elsewhere in the brain need to be caught early.

Questions to Ask Your Care Team

• Will my radiation after surgery be given in one session or several? Why?
• How large is my surgical cavity, and does that affect the dose I can safely receive?
• If I have other brain metastases that weren't removed, how will those be treated?
• How often will I need brain MRIs, and what symptoms should I report between scans?
• What side effects should I watch for, and can I get help with travel for multiple visits?

References

1. Alliance for Clinical Trials in Oncology. "Alliance Trial Finds Fractionated Radiosurgery Reduces Cancer Recurrence After Surgery for Large Brain Metastases." EurekAlert, Sept. 28, 2026.
2. Mayo Clinic News Network. "Study Finds Fractionated Radiosurgery Reduces Recurrence After Surgery for Brain Metastases, May Improve Survival." Sept. 28, 2026.
3. CancerNetwork. "Fractionated SRS Tops Single-Fraction SRS After Brain Metastasis Resection." Sept. 28, 2026.
4. Healio. "Multi-Fraction Radiation Significantly Improves Local Control for Large Brain Metastases." Sept. 28, 2026.

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