Men undergoing treatment for prostate cancer could be safely exposed to fewer radiotherapy sessions, a big trial has found. The trial, conducted by the Royal Marsden NHS foundation trust and the Institute of Cancer Research in London, found that radiotherapy doses can be cut by three-quarters, meaning that five higher doses of radiotherapy are just as effective as 20 smaller doses delivered over several weeks. The study also found that after five years, 96% of the men who received five doses of the multibeam radiotherapy were cancer-free, compared with 95% who received at least 20 doses of standard radiotherapy. Prof Nicholas van As, the medical director of the Royal Marsden hospital and the lead researcher of the study, said the results were “outstanding and fantastic” for prostate cancer patients. He said: “Standard radiation treatment is already highly effective and is very well tolerated in people with localised prostate cancer, but for a healthcare system and for patients to have this treatment delivered just as effectively in five days as opposed to four weeks is hugely significant. “To be able to sit with a patient and say ‘We can treat you with a low-toxicity treatment in five days, and your chance of keeping the cancer at bay for five years is 96%’ is a very positive conversation to have.” With more than 1.4 million cases diagnosed worldwide every year, prostate cancer is the most common cancer occurring in men. In the UK, one in six men are diagnosed with the disease in their lifetime. Almost 12,000 men a year die from the disease in the UK, and although many prostate cancers are slow-growing and may not cause a man harm, with eight in 10 men diagnosed in England living for at least 10 years after their diagnosis, others can be more aggressive and harder to treat. Alistair Kennedy-Rose, 64, from the West Midlands, was diagnosed with prostate cancer in 2014 and took part in the study. Speaking of his treatment at the Royal Marsden, he said: “I still find it unbelievable that five days later I finished my treatment. For something as serious as a cancer diagnosis it was incredibly easy.” Simon Grieveson, assistant director of research at Prostate Cancer UK, said: “It’s fantastic to see that this new type of multibeam therapy appears to be just as effective as traditional radiotherapy and could help men get treated more quickly and with far fewer visits to the hospital.” Prof Emma Hall from the Institute of Cancer Research, who is managing the study, said the advances in radiotherapy were “fantastic”. She said: “This is a gamechanger for patients, meaning they receive a highly effective cancer treatment while spending less time in hospital and travelling to appointments. “It’s another example of how the rapidly advancing field of radiotherapy can improve patients’ lives.” The Prostate Advances in Comparative Evidence study compared results from 874 patients in the UK, Ireland and Canada who were assigned either the longer or shorter course of treatment. Five years after treatment, those treated with the shorter course had a 95.7% rate of remaining free of biochemical clinical failure, compared with 94.6% for those treated with conventional radiotherapy. Side-effects were low and not significantly different between the two groups. Findings from the study will be presented on Monday to the American Society for Radiation Oncology in San Diego.