An international study has found that boosting radiotherapy treatment can cut the risk of breast tumours returning by 50%.
The study examined the cases of 5,569 women with breast cancer.
Of these, 95% had undergone complete removal of their tumour. They had all received a standard dose of radiation to the whole breast.
Half were chosen to receive an extra boost of radiation localised to the area where the tumour had been.
After five years, 109 of the women who had received the extra dose of radiation had seen their tumours return.
This compared to 182 women who had not received radiation boosts.
The biggest difference was seen in women under the age of 40. The chances of breast cancer recurring among this age group were cut by 54% if they received the radiation boost.
Professor Harry Bartelink, from the European Organisation for Research and Treatment of Cancer who led the study, said the results were unambiguous.
"Patients who had the boost had an overall local control rate of 95% and survival at five years was 91%.
"These impressive results mean that a boost should now be considered the standard treatment for early breast cancer, particularly in younger women."
Speaking at the European Society for Therapeutic Radiology and Oncology (ESTRO) conference in Istanbul, Turkey, on Tuesday Professor Bartelink said the results showed the treatment was worthwhile.
"It would not have been acceptable to keep giving booster doses to patients without evidence of benefit."
More than 35,000 women in the UK are diagnosed with breast cancer every year - two thirds are alive five years on, although 1,000 die every month from the disease.
A spokeswoman for the charity Breast Cancer Care welcomed the study.
"Anything that is improving treatments is encouraging and we would welcome it," she said.