Giving women fewer but large doses of radiotherapy may be just as effective at cutting the risk of breast cancer returning as more smaller ones, experts said today.
Research published in the journal Lancet Oncology found that 13 larger doses of radiotherapy were just as good at reducing the risk of breast cancer returning as 25 smaller doses.
Not only that, but the doses were believed to be just as safe and did not increase the risk of suffering side effects.
The study, funded by Cancer Research UK, was carried out by a team from the Royal Marsden NHS Foundation Trust, the Gloucestershire Oncology Centre, The Institute of Cancer Research and the University of Wisconsin in the US.
The 10-year trial followed 1,410 women who had a lumpectomy following treatment for early breast cancer and radiotherapy treatment.
They were divided into three groups - one given the standard treatment of 25 doses in five weeks (totalling 50 "grays" - the measurement of radiation - over the period).
The other two groups given 13 doses in larger amounts over the same period (totalling 42.9 grays and 39 grays respectively).
The researchers found that those given 25 doses had a 12.1% 10-year risk of the cancer recurring while the two groups given 13 doses had a 10-year risk of 9.6% (42.9 grays) and 14.8% (39 grays).
Cancer Research UK said that, usually, patients have radiotherapy treatment once a day, from Monday to Friday, with a rest at the weekend.
Fewer treatments could reduce inconvenience to patients and may also be cost effective for the NHS, it said.
Lead researcher, professor John Yarnold, from The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, said: "We think it should be possible to give fewer but higher daily doses of radiotherapy to the breast to prevent cancer from returning without harming the patient's healthy tissues.
"However, we will have to wait for the results of our further trials that have followed this study before we can confirm that the strategy is more effective than the standard treatment in the long term."
Dr Lesley Walker, director of cancer information at Cancer Research UK, said: "This was an extremely important early trial.
"If these results are confirmed in the larger follow-up studies, it could mean better outcomes with less hospital visits for patients and therefore an improvement in their quality of life."
Maria Leadbeater, a specialist nurse for Breast Cancer Care, said: "These early trial results are extremely encouraging. Breast cancer patients tell us of the enormous stress and exhaustion they suffer when forced to travel daily for five weeks of radiotherapy treatment.
"Fewer, more targeted doses could really help ease this burden and reduce the often prohibitive costs patients incur through having to travel miles to the nearest specialist centre for treatment.
"At the same time professionals are struggling to cope with seeing so many patients so regularly.
"If further trials back up these exciting results, it could mean an end to weeks of ongoing treatment and a real, tangible improvement to the quality of patient's lives. We look forward to seeing the results of more research."
Emma Taggart, director of policy and campaigns at Breakthrough Breast Cancer, said: "If further trials confirm these early results then this technique could make a real difference to women with early breast cancer.
"Radiotherapy is important in reducing the chance of cancer coming back, but women tell us that attending many sessions can be both physically and emotionally draining.
"Anything that can improve a patient's experience of breast cancer treatment and is as effective as the current standard, with no increase in side effects, is to be welcomed."