Washington ? Thousands of breast cancer patients are opting for a week of radiation instead of the usual six weeks, thanks to new methods that target cancer-killing beams at the tumor site instead of the whole breast.

Although early research is promising, nobody has proved the faster treatment keeps women cancer-free as long as the old-fashioned kind — or identified who are the best candidates to try it.

Now the National Cancer Institute is racing to start a massive study this fall to test those questions, seeking answers before patient demand for the easier therapy becomes overwhelming.

“This is the golden opportunity,” says Dr. Frank Vicini of William Beaumont Hospital in Royal Oak, Mich., a pioneer of the one-week approach who is helping to plan the research. “If we don’t do it now, it’s not going to happen.”

The hurry is in hope of avoiding past mistakes when enthusiasm outpaced evidence for new treatments. For example, doctors for years urged hormone therapy after menopause, until women were studied carefully enough to tell that long-term use actually was risky.

Popular choice

Already, the new radiation approach, called partial-breast radiation, is rapidly gaining in popularity. More than 2,200 patients have been treated by one method of partial-breast radiation alone — a machine called the MammoSite that places a radioactive seed inside the breast. Some 267 health care centers now offer MammoSite, and untold others offer other forms of partial-breast radiation.

Some patients choose it for convenience, others because they live too far from a radiation facility to make getting the traditional six, sometimes seven, weeks of daily treatments doable.

“If radiation resources are virtually inaccessible to you, then maybe the shortened course would be preferred,” said Dr. Paul Wallner of the NCI.

But, he said, “patients should be aware this has not withstood the test of time.”

Life-or-death options

About 70 percent of the 203,000 women estimated to be diagnosed with breast cancer this year will qualify for a lumpectomy — removing just the tumor, not the whole breast. Radiation afterward is crucial to kill any stray cancer cells lurking nearby. With proper follow-up care, lumpectomies have proved as good at curing early-stage breast cancer as breast-removing mastectomies do.

But because traditional whole-breast radiation takes so long, doctors say many women choose a more disfiguring mastectomy — or forego radiation, thus running a big risk of the cancer returning.

Partial-breast radiation takes only about five days, packing in larger doses because a much smaller amount of tissue is being beamed. Doctors either focus standard external radiation equipment to where the tumor was excised, or they use a method called brachytherapy — inserting radioactive seeds into the tumor site through spaghetti-like tubes. Doctors can either hand-place the seeds or use MammoSite.

A handful of studies — including one published last week by Vicini — have tracked small numbers of patients for five years and suggest that both partial- and whole-breast radiation are equally effective.

Research limited

Those studies typically restrict partial-breast radiation to carefully selected women — those with very small tumors that, upon removal, showed wide margins of cancer-free tissue and no signs of spread. The women also tend to be in their 40s or older, although doctors disagree on age cutoffs. Vicini says about a third of lumpectomy patients meets those criteria.

One big question is whether it’s OK for more women to try partial-breast radiation. That’s a question the NCI-funded study should help answer. It will enroll at least 6,000 women, comparing the two radiation approaches for long-term effectiveness. NCI hopes to begin the study this fall, when it will announce how to volunteer.

Also, MammoSite’s maker plans to track 2,500 recipients to see how they fare long-term; 450 are enrolled in this registry so far.

Until the final proof is in, what should physicians tell women?

“I consider it an option for women, and I tell them that because we haven’t been doing brachytherapy as long as whole-breast radiation, there are still some unknowns,” says Dr. Troy Scroggins of New Orleans’ Ochsner Clinic Foundation, which has treated about 200 patients.