Cancer patients can get their radiotherapy over with more quickly without affecting their survival, research suggests.
A clinical trial of patients with lung cancer found they were just as likely to live if they had radiotherapy once a day for six and a half weeks, as if they had it twice a day for three weeks.
The study, presented at the American Society of Clinical Oncology (ASCO) conference in Chicago, was carried out on people with small cell lung cancer that had not spread around the body.
There are around 45,500 new cases of lung cancer in the UK every year, and about 12% of these are small cell lung cancer.
The group of 550 people in the research were split into two groups, each receiving a different radiotherapy regime combined with chemotherapy.
Researchers found that survival in both groups was similar, with 56% of patients who had radiotherapy twice a day surviving for two years compared with 51% of those given it once a day.
Side effects were similar between the two groups.
Professor Corinne Faivre-Finn, a Cancer Research UK-funded scientist from the University of Manchester and the Christie Hospital, who led the trial, said: "Before this study it was unclear whether having radiotherapy once or twice a day helped more patients survive for longer and what level of side effects was expected with modern radiotherapy techniques.
"We're pleased to provide answers to these questions and our results have already begun to change practice around the world.
"Based on our findings, small cell lung cancer patients will be able to choose between a shorter course of radiotherapy given twice a day and a longer course given once a day."
Dr Ian Walker, Cancer Research UK's director of clinical research, said: "Finding the most appropriate way to give treatments like radiotherapy is a crucial part of treating cancer.
"Before this study began there had been few large clinical trials of this type in small cell lung cancer.
"Outcomes for lung cancers have been very poor for a long time, so at Cancer Research UK we're dramatically increasing the amount we're spending on research in this area."