By Dennis Thompson
SUNDAY, May 31, 2015 (HealthDay News) -- Using radiation on the entire brain to prevent new tumors from forming in patients whose cancer has spread to the brain can have a devastating effect on their ability to think and remember, compared with more targeted treatment, new findings show.
Nearly all patients who received whole-brain radiation therapy -- 92 percent -- experienced a decline in memory and verbal ability, researchers reported Sunday at the American Society of Clinical Oncology (ASCO) annual meeting in Chicago.
By comparison, only 64 percent of patients who were given targeted radiosurgery, which focuses on a limited and tightly controlled area of the brain, experienced declines in mental ability.
"Essentially, the brain does not like to be irradiated," said senior study author Dr. Jan Buckner, a professor of oncology at the Mayo Clinic in Rochester, Minn.
The study also found that patients who received whole-brain radiation therapy did not live any longer than those who went through more targeted radiation, even though they were less likely to experience recurring brain tumors.
Buckner and study author Dr. Paul Brown both said that's because these patients end up dying from the primary cancer present elsewhere in their bodies that is also causing brain tumors. While they are alive, radiosurgery can be used to attack any new tumors that pop up.
"If patients develop new lesions, we just treat them with radiosurgery," said Brown, a professor of radiation oncology at the University of Texas MD Anderson Cancer Center in Houston. "The risks and side effects outweigh the benefits of whole-brain radiation therapy."
It's estimated that each year as many as 400,000 Americans will experience cancer that spreads to the brain from other areas of the body, often the lungs or the breast. And about 200,000 of those patients will receive whole brain radiation therapy, according to background information with the study.
Whole-brain radiation therapy involves exposing the entire brain to 20-minute doses of radiation once a day for between 10 and 15 days, Brown said.
By comparison, radiosurgery involves very focused beams of radiation that can be aimed with millimeter precision and only involve a single treatment. Buckner likened it to the sunbeam produced by a magnifying glass.
Up to now, doctors have tended to treat cancer patients who have developed brain tumors that spread from other parts of the body by first using targeted radiosurgery to treat the lesions, and then using whole-brain radiation therapy to reduce the likelihood of future tumors cropping up, Brown said.
That strategy has been based on earlier studies that found whole-brain radiation is much better at preventing future brain lesions, and that tumors are more likely to recur in patients who receive radiotherapy alone, he said.
But based on these new findings, doctors likely will begin recommending whole-brain radiation therapy only for patients with aggressive brain cancer or with other cancers that tend to cause many brain tumors, said Dr. Brian Michael Alexander, a radiation oncologist at Dana-Farber Cancer Institute and a professor of radiation oncology at Harvard Medical School in Boston.
"This study will help shape treatment decisions for thousands of current and future patients," he said. "As doctors, we want the very best for our patients, and sometimes giving less treatment offers the best result."
Alexander said he has some cancer patients he has treated "for years" with targeted brain radiosurgery, zapping new lesions as they occur, without ever resorting to whole-brain radiation therapy.
In the study, 213 patients with cancer that had spread to their brains received radiosurgery, and then about half also received follow-up whole-brain radiation therapy. All of the patients had one to three small brain tumors, up to 3 centimeters in width.
Follow-up tests of mental ability found that patients who received whole-brain radiation therapy experienced a 30 percent decline in immediate recall, compared with 8 percent of patients who only received radiosurgery. Immediate recall is the ability to hold onto a small amount of information over a few seconds.
In addition, whole-brain radiation patients experienced a greater decline in short-term memory, an average 51 percent compared with a 20 percent decline in radiosurgery patients.
Verbal ability also took a hit, with whole-brain radiation patients experiencing an average 19 percent decrease compared with just 2 percent of radiosurgery patients.
Patients who underwent whole-brain radiation therapy also experienced significant declines in their quality of life compared with radiosurgery patients, Brown said.
Brown said doctors likely will begin recommending radiosurgery alone, combined with close monitoring, for many patients with brain tumors.
Whole-brain radiation therapy will be reserved for patients who have larger brain lesions, or who have more advanced cancer, he said.
"The role for whole-brain will be pushed back toward a patient's later stages, when they have limited options at that point," Brown said.
The study received funding from the U.S. National Institutes of Health.
Data and conclusions presented at meetings are usually considered preliminary until published in a peer-reviewed medical journal.