The side effects of radiation therapy are either described as acute or late.
Acute side effects are those that happen during and within a few weeks after treatment. They are usually more temporary and tend to resolve, although this is not always the case. Sometimes severe acute side effects can result in late effects.
Late side effects are side effects that can occur three months after completing radiotherapy. These are less common and may not show themselves during or immediately after radiotherapy but occur later on. The risk with late side effects is that they could be permanent or irreversible and become a more long-term situation.