MIAMI (AFP) - Two thirds of women diagnosed with early stage breast cancer in the United States get radiation for twice as long as recommended, researchers said Wednesday.

The findings in the Journal of the American Medical Association (Jama) showed that most women get six to seven weeks of radiation therapy, despite new guidelines issued after multiple randomised trials showing that three weeks of a stronger type of radiation - called hypofractionated whole breast radiation - costs less and works just as well after breast-conserving surgery.

Hypofractionated radiation involves higher doses of radiation delivered over the course of three to four weeks, instead of the traditional treatment of lower dose radiation for five to seven weeks.

"Hypofractionated radiation is high-value care and high-quality breast cancer treatment that saves the health care system money," said senior author Ezekiel Emanuel, chairman of Penn's Department of Medical Ethics and Health Policy and a breast oncologist.

"It's a win-win. And yet, only a third or fewer women are getting it in the US, while in other countries over 70 per cent of women receive hypofractionated treatment."

Four randomised trials and 2011 practice guidelines from the American Society for Radiation Oncology (Astro) support the shorter duration treatment.

The use of hypofractionated therapy is on the rise in the United States. The Jama study found that 34.5 per cent of women over 50 years old received it in 2013, up from 10.6 per cent in 2008.

In younger women and those with more advanced cancers, 21.1 per cent of women received hypofractionated therapy last year, up from 8.1 per cent in 2008.

However, the United States still lags far behind Canada and Britain, where more than seven in 10 early breast cancer patients get shorter radiation treatments.

The problem in the United States comes down to a lack of financial incentive for shorter, more effective care, said Emanuel.

"The current payment structure is the biggest hurdle - there is no financial incentive to recommend shorter duration treatment," he said.

"We need to properly align payment with health care quality in order to reduce low-value cancer care."