BACKGROUND: Peritumoral normal tissue is inevitably also irradiated during 
radiotherapy, depending on the location and size of the target volume as well as 
the cumulative dose. Depending on the temporal course after irradiation acute, 
subacute, and chronic alterations are described in co-irradiated normal tissue 
that can be detected by imaging. Radiation damage can be transient or 
persistent.
OBJECTIVE: This article gives an overview of the most important signs of 
radiation-induced radiogenic alterations to tissue in various organ systems.
FINDINGS: Frequent radiation-induced tissue alterations found by imaging are 
pneumonitis, disturbance of the blood-brain barrier, radionecrosis of brain 
tissue, radiogenic liver damage, mucositis, colitis, osteitis, 
osteoradionecrosis and myositis. The combination with systemic chemotherapy or 
immunotherapy can increase the severity of radiogenic reactions of normal 
tissue.
RECOMMENDATIONS FOR AFTERCARE: The most important differential diagnosis for 
radiogenic alterations to normal tissue is post-therapeutic tumor recurrence. 
Besides typical latency periods, location and matching with the radiation field 
are important differentiation criteria, depending on the tumor biology and the 
radiation technique. The follow-up schedule should follow the current guidelines 
and the clinical condition of the patient should be additionally considered. The 
radiologist needs to be familiar with the typical imaging morphology of 
radiogenic tissue changes to avoid false interpretation during follow-up 
investigations.