Radiotherapy can control aggressive bladder cancer as well as surgery, research has shown.
The findings could spare many patients the necessity of having their bladders removed.
Bladder removal is standard treatment for aggressive bladder cancer, but has a severe effect on quality of life.
A study of 219 patients with advanced bladder cancer found that radiotherapy prevented tumours returning in more than 60% of cases for at least two years.
For many whose cancer did return, the disease was non-aggressive and only needed local treatment.
After five years, survival rates for whole organ radiotherapy and radiotherapy directed at a specific target in the bladder were both around 40%. This was about the same as for patients who have their bladders removed.
In addition, radiotherapy produced a low risk of severe side effects.
The study, funded by Cancer Research UK, is published in the International Journal of Radiation Oncology Biology Physics.
Lead investigator Dr Robert Huddart, from the Institute of Cancer Research in London, said: " Our study was part of the largest ever clinical trial of radiotherapy in bladder cancer and shows that patients with the disease can be treated effectively with radiotherapy. With similar success rates to surgery and fewer side effects whilst allowing patients to retain a functioning bladder, radiotherapy should be seen as an alternative to surgery.
"The introduction of image guided radiotherapy and more sophisticated ways of giving radiotherapy will hopefully further reduce any side effects that patients experience."
Kate Law, director of clinical research at Cancer Research UK, said: "Previous results from this trial changed how doctors treat bladder cancer, showing that giving patients chemotherapy and radiotherapy is better than radiotherapy alone.
"Many thousands of patients take part in Cancer Research UK-funded clinical trials every year, and it's only by carrying out studies like this that we can test different approaches to find the most effective and safest treatments."