It may seem surprising but although doctors have known for more than 50 years that radiotherapy can often relieve the pain caused by secondary bone cancer, the way in which the treatment actually works is still not understood.

Often x-rays and scan tests will show some reduction in tumour seedlings, and healing of the damaged bone, in the months after radiotherapy. But equally often those same tests will show no change at all, even when there has been excellent pain relief.

Despite the uncertainty about how it works the evidence for the value of radiotherapy in this situation is overwhelming. Overall about 7 out of 10 people get good pain relief, and of those about 3 out 10 get complete freedom from pain. The improvement is not immediate, and usually takes between 7 to 10 days after treatment to become apparent and then sometimes as long as 4 to 6 weeks to get the full benefit. Some people find the treatment gives permanent pain relief but on average the improvement lasts about 3 to 4 months, but the treatment can often be repeated if the pain does come back.