SAN ANTONIO - New research casts doubt on a popular treatment for breast cancer: a week of radiation to part of the breast instead of longer treatment to all of it.

Women who were given partial radiation were twice as likely to need their breasts removed later because the cancer came back, doctors found.

The treatment uses radioactive pellets briefly placed in the breast instead of radiation beamed from a machine. At least 13 percent of older patients in the United States get this now, and it is popular with working women.

"Even women who aren't working appreciate convenience," but they may pay a price in effectiveness if too little tissue is being treated, said study leader Benjamin Smith of MD Anderson Cancer Center in Houston.

Results were to be reported Wednesday in San Antonio.

About 230,000 cases of breast cancer are diagnosed each year in this country, most in an early stage. Typical treatment is surgery to remove the lump, followed by radiation every weekday for five to seven weeks. That's tough, especially for older women and in rural areas.

Doctors hoped a shorter approach, brachytherapy, would be just as good with fewer side effects. To do it, they temporarily place a thin tube into the cavity where the tumor was.

Treatment takes only five days and the total radiation dose is comparable to the longer method. But a smaller area - just around the lump - gets treated instead of the whole breast.

Researchers looked at Medicare records on 130,535 women who had lumps removed and radiation. Less than 1 percent chose brachytherapy in 2000; that rose to 13 percent by 2007.

After accounting for differences in age, tumor size, and other factors, researchers found that within five years, 4 percent of brachytherapy patients needed surgery to remove the breast where the original tumor had been vs. 2 percent of those given traditional radiation. Hospitalization, infections, broken ribs, and breast pain also were more common with brachytherapy.