Radiation necrosis is a significant and often dose limiting side effect of external beam radiation therapy. Because of the variable levels of uptake, which can often be quite intense, the pattern of uptake may be more helpful in differentiating benign and malignant uptake.

Inflammation and changes of radiation pneumonitis are common occurrence following thoracic radiation that can pose a diagnostic problem on both anatomic and functional images. FDG uptake in the lungs may be minimal to moderately high usually in the involved portion of the lung due to associated inflammation. Therefore, without the pertinent clinical history, differentiation of tumor recurrence from inflammation might be somewhat difficult.

Images can demonstrate changes directly with in the radiation field as well as at the periphery as can bee seen in the apices following neck radiation. Other associated changes in soft tissue and/or osseous structures may be seen as well.