Typical manifestations of post-radiotherapy tissue injury on FDG-PET/CT

Learning Objectives 1. Briefly review the pathophysiology of radiation injury. 2. Familiarize physicians interpreting oncologic PET/CT scans with common manifestations of post-radiation changes, with an emphasis on CT findings.

FDG-PET/CT has become instrumental in the initial and post-treatment evaluation of patients with numerous malignancies. For a large proportion of patients, external beam radiation therapy (XRT) is a component of the treatment regimen. However, in the course of irradiating the target lesion, adjacent non-target tissues often receive a substantial radiation dose, which can result in both functional and morphologic changes. The purpose of this exhibit is to familiarize interpreters of oncologic FDG-PET/CT scans with typical functional and anatomic changes that occur in the setting of radiotherapy. The exhibit will briefly review the pathophysiology and common underlying mechanisms mediating radiation injury to tissues. Thereafter the common CT and PET findings of radiation injury will be reviewed, including tissue injury within the lungs, bones and bone marrow, bowel, and brain, with discussion of the timing and evolution of these findings, where appropriate. After reviewing the exhibit, the attendee will be able to more confidently ascribe findings either on the PET or CT components of the exam as related to radiation effects. This should limit unnecessary imaging followup and perhaps avoid biopsy of incidental or otherwise uncertain findings, resulting in reduced medical system costs, patient inconvenience, and potential complications