A game-changing "search and destroy" treatment could offer hope of a longer life to thousands of men with incurable prostate cancer.
The first two British patients were treated last weekend, after research found that it could significantly extend survival for men with no other options.
Charities said they were "thrilled" by the promise shown by the treatment, which identifies and attacks a protein expressed on the surface of prostate cancer cells. One in five men lived for almost three years after receiving the targeted radiotherapy.
Medics at the world's largest cancer conference in Chicago said the treatment was a "huge" breakthrough, giving hope to around 5,000 men diagnosed with advanced prostate cancer in Britain each year.
The method, which experts described as delivering "a bullet instead of a light", is based on imaging techniques that light up tumours in order to plan treatment. The technique simultaneously delivers a radioactive payload.
The technique - called prostate-specific membrane antigen (PSMA) radiotherapy - has been dubbed a "search and destroy" method of treatment.
It uses a radioactive isotope, which binds to a protein on the surface of malignant cells, attacking them without damaging surrounding tissues.
Prof Johann de Bono of the Institute of Cancer Research in London, who is co-leading a global study, said: "It is a huge deal... one of the next big things. There is no doubt it is causing substantially durable remission."
Arun Azad, an Australian oncologist involved in one of 10 trials now taking place, said: "It is potentially game changing. If the results are positive it really will change the landscape of how we treat prostate cancer."
He said about half of the 10,000 men diagnosed with advanced prostate cancer in Britain each year may benefit and the treatment could ultimately be offered to patients at an earlier stage.
"If we can bring it forward, then it really is transformational," he said.
Prof Stefano Fanti of the University of Bologna, said: "The concept is very simple. What we see is what you treat. Essentially what you have is a bullet instead of a light."
An Australian study of 50 men found that on average it extended survival from nine to over 13 months. One in five was alive almost three years later.
The pioneering technique is being offered privately in the UK, but is more widely available in Australia and Germany. It involves up to six treatments, every six to eight weeks, costing around £12,000 each in the UK.
Experts hope that it will be rolled out on the NHS, if trials prove successful.
Dr Matthew Hobbs, from Prostate Cancer UK, said he was "thrilled" to see the trial results.Last weekend, Hans Schaupp, 77, became the first man in Britain to be treated with the new technique.
Mr Schaupp, from Liphook, Hants, said he had suffered no side effects since undergoing treatment at a clinic in Windsor run by GenesisCare.
"The treatment is fantastic. Because it is targeted it makes so much more sense," he said. "Rather than poisoning your whole body with chemotherapy, it goes straight to the tumours."
A separate study by researchers in Australia and New Zealand found giving men treatment earlier with the drug enzalutamide could cut the chance of an early death by a third.