The probability of survival at the 10-year mark was also similar: 84.4 percent for the standard group and 84.6 percent for the accelerated group.
Whelan said that, for some women, an accelerated schedule could be a welcome alternative.
"Some women are reluctant to have breast-conserving surgery because of the need to undergo the lengthy radiation treatment, typically six weeks," he said.
Another breast cancer expert said that she had also found positive results with shorter radiation treatments.
Dr. Manjeet Chadha, associate chairwoman of radiation oncology at Beth Israel Medical Center and associate professor of radiation oncology at the Albert Einstein College of Medicine in New York City, found that a three-week course of radiation works well for early-stage breast cancers.
She presented her findings in late last year at the annual meeting of the American Society for Radiation Oncology.
But she cautioned that while the new finding, coupled with her study's results, are promising, they don't apply to all women with breast cancer. Participants in Whelan's study, for instance, had to have negative axillary lymph nodes and clear resection margins.
What that study does reveal, she said, is "that in the node-negative patient, when you don't require chemo, you can get similar results with the abbreviated [course]."
But what is yet to be researched thoroughly, she said, is how well the shorter radiation course works for women who have breast-conserving surgery and do need chemo. About 11 percent of the women in Whelan's study also had chemotherapy.
Even so, Chadha said, the new study is important "because it does present an alternative for early-stage breast cancer patients."
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