October 2, 2013 — Between 1999 and 2002, the UK Standardization of Breast Radiotherapy (START) trials recruited 4,451 women from 35 radiotherapy centers across the U.K. START A compared the international standard, a total dose of 50 Gy delivered in 25 doses of 2 Gy over 5 weeks with 41.6 Gy of 3.2 Gy and 39 Gy of 3 Gy given in 13 treatments over 5 weeks. START B compared the standard (50 Gy given in 25 doses of 2 Gy over 5 weeks) with 40 Gy delivered in 15 doses of 2.67 Gy over 3 weeks (hypofractionated).
After 10 years, tumor control rates in START A were similar between the three schedules with very few women experiencing a relapse of their cancer (7.4% after 50 Gy, 6.3% after 41.6 Gy, and 8.8% after 39 Gy) and with much the same damage to surrounding healthy breast tissue.
Likewise, in START B, the number of women whose cancer had returned in the breast remained similar in both schedules at 10 years (5.5% after 50 Gy and 4.3% after 40 Gy). Moreover, with the shorter 40 Gy 15-dose schedule, there was significantly less harm to healthy tissue while the unexpected survival benefit seen at five years persisted. These outcomes were similar irrespective of age, tumor grade, stage, chemotherapy use or use of tumor bed boost.
"These 10 year results reassure us that three weeks of radiotherapy is as good as the five weeks still used in many countries with less damage to nearby healthy tissue, as well as being more convenient for women (shorter waiting lists and fewer hospital visits) and cheaper for health services,” explained John Yarnold, professor, study leader from The Institute of Cancer Research, London, and The Royal Marsden NHS Foundation Trust, in The Lancet Oncology. "The upshot is that, contrary to conventional thinking, cancer cells are just as sensitive to the size of daily radiotherapy dose as the normal tissues responsible for late onset side effects, meaning the continued use of traditional lower (2 Gy) doses spares the cancer as much as the healthy tissue, offering no benefit to patients. Our results support the continued use of 40 Gy in 15 fractions, which has already been adopted as the standard of care by most U.K. centers."
April 15, 2026 
