18F-FES Uptake in Radiation Pneumonitis

18 F-FDG uptake in radiation pneumonitis is well documented; however, the same is less so for 18 F-floroestradiol (FES), which specifically binds to the estrogen receptors in vivo. We observed increased FES uptake in the right lung of an estrogen receptor positive breast cancer patient who had undergone right modified radical mastectomy followed by radiation therapy to chest wall. The possibility of FES uptake in radiation pneumonitis must therefore be kept in mind while interpreting FES PET.