By Symeon Missios, MD, Long Island Brain & Spine

A woman in her late fifties sits across from me with her husband. She finished treatment for lung cancer a little over a year ago, and her scans since then have been clean. Last week she had a brain MRI because words had started slipping away from her in the middle of sentences. The scan showed seven small metastases scattered across both sides of the brain.

She has already done some reading. Before I can say much, she asks the question she came in with.

“Seven is a lot, isn’t it? Doesn’t that mean whole-brain radiation?”

Fifteen years ago, the answer would usually have been yes. Today it usually is not. The number of tumors on a scan still matters, but it matters far less than most patients, and a fair number of physicians, assume. This is how I think through that decision.

What Brain Metastases Are

Brain metastases are tumors that begin elsewhere in the body, most often in the lung, breast, skin (melanoma), or kidney, and reach the brain through the bloodstream. They are becoming more common, largely because patients are living longer with cancer that is controlled elsewhere. I covered diagnosis and surgical management in an earlier article on brain metastases. The question here is narrower: when there is more than one tumor, what is the best way to treat them?

The Old Rule: Count the Tumors

For a long time, the treatment plan followed the count. One tumor, or perhaps two or three, could be treated with surgery or radiosurgery. Beyond that, the default was whole-brain radiation therapy, which treats the entire brain over about two weeks and addresses every visible tumor and every microscopic one at the same time.

Whole-brain radiation works. It controls existing tumors reasonably well and lowers the chance of new ones appearing. Its cost is paid in memory and thinking. In a randomized trial of patients with one to three metastases, cognitive decline at three months occurred in 92 percent of patients who received radiosurgery plus whole-brain radiation, compared with 64 percent of those treated with radiosurgery alone, and survival was no different between the groups [1]. An earlier trial was stopped early because memory decline in the whole-brain group was roughly twice as common [2].

Patients describe trouble finding words, difficulty following a conversation, and fatigue that lingers for months. For someone who may live for years, that is a significant price.

What Radiosurgery Does Differently

Stereotactic radiosurgery delivers a high, precisely shaped dose of radiation to each tumor while sparing the brain around it. There is no incision. I explain the basics in Stereotactic Radiosurgery: The “Surgery” That Doesn’t Cut. The important point for multiple metastases is that each tumor is targeted individually, and the healthy brain between tumors receives comparatively little radiation.

When radiosurgery required a rigid head frame and treated one target at a time, a patient with seven or ten tumors faced a very long day, and that practical barrier helped keep the counting rule in place. Modern platforms have largely removed it. At Good Samaritan we use the Varian Edge with HyperArc, which plans and treats multiple targets in a single session using a custom-fitted mask instead of a frame. We have treated patients with as many as fifteen metastases in a session of about twenty minutes.

What the Evidence Says About Numbers

The real clinical question is whether patients with many tumors do as well with radiosurgery as patients with a few. The best answer comes from a large prospective study in Japan that followed nearly 1,200 patients treated with radiosurgery alone. Patients with five to ten metastases had the same median survival as patients with two to four, just under eleven months in both groups, and serious side effects were equally uncommon [3].

More recently, a randomized trial published in JAMA in 2026 compared stereotactic radiation with a memory-sparing form of whole-brain radiation in 196 patients who had five to twenty metastases. Patients treated with stereotactic radiation reported a lower symptom burden over the following six months, and survival at one year was essentially the same in both groups [4].

Joint guidelines from the American Society of Clinical Oncology, the Society for Neuro-Oncology, and the American Society for Radiation Oncology reflect the same shift: radiosurgery for patients with a limited number of metastases, and deliberate protection of memory whenever whole-brain treatment is used [5].

Why the Count Matters Less Than the Volume

If the number of tumors is no longer the deciding factor, several other things are. In practice I weigh them together:

• Total tumor volume. Ten tiny metastases can carry less risk than two large ones.
• The size of the largest tumors. Tumors larger than about three centimeters often do better with surgery first.
• Symptoms and swelling. A tumor causing significant pressure or a neurological deficit may need to be removed rather than radiated.
• The type of cancer. For melanoma, lung cancers with specific mutations, and HER2-positive breast cancer, drug treatments that reach the brain can play a large role.
• How well the cancer is controlled elsewhere. A patient with stable disease outside the brain has the most to gain from protecting cognition.
• How quickly new tumors are appearing. Many new metastases between scans may favor treating the whole brain.

That last point is the real trade-off. Radiosurgery treats what is visible. It does not treat what is not yet visible. Patients treated with radiosurgery alone are more likely to develop new metastases later [1, 2], which is why they need MRI surveillance, usually every two to three months at first. When new tumors appear, they can usually be treated with radiosurgery again.

When Surgery Comes First

Surgery is usually the better first step when a tumor is large, when it is causing significant swelling or pressure, when tissue is needed for diagnosis, or when a tumor in the back of the brain threatens to block the flow of spinal fluid. The value of removing a single metastasis was established in a randomized trial more than three decades ago, in which surgery plus radiation reduced recurrence and lengthened both survival and the time patients remained functionally independent [6]. Today, after removing a metastasis, we typically treat the surgical cavity with radiosurgery rather than radiating the whole brain.

Many patients with multiple metastases end up with a combination: one large, symptomatic tumor that I remove, and several smaller ones treated with radiosurgery in the weeks that follow.

When Whole-Brain Radiation Still Makes Sense

Whole-brain radiation has not disappeared. It remains reasonable for patients with very many tumors or a rapidly rising number, and for cancer that has spread along the lining of the brain. When we use it, current practice is to spare the hippocampus, the structure most responsible for forming new memories, and to add the medication memantine. In a large randomized trial, that combination reduced the risk of cognitive decline by about a quarter without affecting survival or tumor control [7].

What Treatment Is Like

Radiosurgery is an outpatient procedure. Planning involves a high-resolution MRI, a CT scan, and a thermoplastic mask molded to the face. During treatment the mask keeps the head still while the machine moves around it in a series of arcs, and nothing is felt. Most patients go home the same day. Short-term effects can include fatigue, headache, and occasionally temporary swelling that responds to steroids. The longer-term effect we watch for is radiation necrosis, an inflammatory reaction that can appear months later and resemble tumor growth on MRI. It is uncommon and usually manageable.

Each case is reviewed at the Cancer Institute at Good Samaritan by a neurosurgeon, a radiation oncologist, and the patient’s medical oncologist. More about the program is on our radiosurgery page and in Everything You Need to Know About Stereotactic Radiosurgery.

The Bottom Line

Having several brain metastases no longer automatically means whole-brain radiation. For many patients, including those with five, ten, or more small tumors, radiosurgery can treat every visible lesion in a single session while largely preserving memory, with survival similar to that of patients who have fewer tumors. The trade-off is a higher chance of new tumors later, which is managed with regular MRI and further treatment when needed.

For the woman I described, that meant radiosurgery to all seven tumors in one session, followed by an MRI every two months.

If you or a family member has been told that multiple brain metastases mean whole-brain radiation, it is reasonable to review the alternatives before treatment begins. Our offices in West Islip and Smithtown and the Cancer Institute at Good Samaritan see patients for consultation and second opinions. Please bring the MRI itself on disc, not only the written report, along with recent notes from your oncologist. For comprehensive brain and spine care across the practice, you can also reach Long Island Brain & Spine at longislandbrainandspine.com. If you develop new weakness, confusion, a seizure, or a severe headache with vomiting, go to the nearest emergency department.

Dr. Symeon Missios is a board-certified neurosurgeon practicing on Long Island, with expertise in brain and spine surgery, cerebrovascular disease, and stereotactic radiosurgery. To schedule a consultation or second opinion, request an appointment or call (631) 422-5371 or toll-free (888) 737-5427.

References

1. Brown PD, Jaeckle K, Ballman KV, Farace E, et al. Effect of radiosurgery alone vs radiosurgery with whole brain radiation therapy on cognitive function in patients with 1 to 3 brain metastases: a randomized clinical trial. JAMA. 2016;316(4):401–409. PubMed: 27458945
2. Chang EL, Wefel JS, Hess KR, Allen PK, et al. Neurocognition in patients with brain metastases treated with radiosurgery or radiosurgery plus whole-brain irradiation: a randomised controlled trial. Lancet Oncol. 2009;10(11):1037–1044. PubMed: 19801201
3. Yamamoto M, Serizawa T, Shuto T, Akabane A, et al. Stereotactic radiosurgery for patients with multiple brain metastases (JLGK0901): a multi-institutional prospective observational study. Lancet Oncol. 2014;15(4):387–395. PubMed: 24621620
4. Aizer AA, Shin KY, Catalano PJ, et al. Treatment for brain metastases with stereotactic radiation vs hippocampal-avoidance whole brain radiation: a randomized clinical trial. JAMA. 2026;335(13):1127–1136. PubMed: 41712219
5. Vogelbaum MA, Brown PD, Messersmith H, Brastianos PK, et al. Treatment for brain metastases: ASCO-SNO-ASTRO guideline. J Clin Oncol. 2022;40(5):492–516. PubMed: 34932393
6. Patchell RA, Tibbs PA, Walsh JW, Dempsey RJ, et al. A randomized trial of surgery in the treatment of single metastases to the brain. N Engl J Med. 1990;322(8):494–500. PubMed: 2405271
7. Brown PD, Gondi V, Pugh S, Tome WA, et al. Hippocampal avoidance during whole-brain radiotherapy plus memantine for patients with brain metastases: phase III trial NRG Oncology CC001. J Clin Oncol. 2020;38(10):1019–1029. PubMed: 32058845