FDG - PET/CT in patients with parenchymal changes attributed to radiation pneumonitis (RP).

INTRODUCTION: Radiation Pneumonitis /RP/ can be an adverse complication of radiotherapy /RT/ and can limit the application of the already planned radiation dose. It is often associated with radiotherapy of lung carcinoma and is occasionally caused by radiation therapy of breast carcinoma and lymphomas located in the mediastinum. PET-CT emerges lately as a prospective modality for early diagnostics of RP. Aim of this study was to summarize the initial data from the diagnostic application of PET-CT in patients suspicious of RP and to derive criteria, which can help differentiate RP from early recurrence of the disease and/or residual tumor.
METHODS: The current study included 23 patients, who had metabolic (PET) and anatomical (CT) changes consistent with RP. We additionally defined the metabolic activity (SUVmax) in the lung parenchyma of 20 patients without RT.
RESULTS: All patients had increased metabolic activity in the lung parenchyma involved in the irradiated area with a mean of SUVmax3,45 /ranging between 1 and 7,1/. The control group had a physiological background metabolic activity - SUVmax0.61 +/- 0.11.
DISCUSSION AND CONCLUSION: Metabolic changes in the patients suspicious of RP involved diffusely increased metabolic activity coinciding with the anatomical changes in the irradiated area. 3/23 patients had a proven recurrence of the primary neoplastic process in the irradiated area. The metabolic changes in those patients involved - increase in the metabolic activity at follow up or lack of tendency towards normalization after chemotherapy, which implied the existence of still viable tumor cells. Our initial experience in the diagnostic application of 18F-FDG PET/CT in patients suspicious of RP, allows us to summarize the following - PET/CT is a reliable imaging modality in the diagnostics of RP. Through its sequential use, we can differentiate inflammatory changes related to RP from early recurrence of the primary neoplastic process.