How does radiotherapy help brain tumor? is it only a temporary treatment?

Tumor treatment: Radiation has been used for decades to attempt to destroy abnormal cancer tissue throughout the body. More recently, this has been defined with the usage of a focal gamma "knife" which decreases the risk of damaging normal brain tissue. The theory involves shrinking or debulking the brain tumor mass. Although in some cases this may be long lasting, in others there may only be brief benefit.