Temporal changes of FDG uptake in post radiation pneumonitis

Objectives To evaluate temporal changes and patterns of increased FDG activity in radiation induced pneumonitis in the patient having lung cancer treated with radiation therapy by utilizing a dual-time point PET imaging

Methods 62 dual-time point PET imaging of the chest in 25 patients who received radiation therapy were retrospectively analyzed to see 1). how long metabolic activity lasts, 2) how high metabolic activity increases-degree of increased metabolic activity, 3). patterns of increased metabolic activity-focal vs. diffuse.Final outcome is determined by histology, biopsy or cytology and follow-up with CT or PET for 2 years. Data analysis included SUV max at initial and delayed scan, % change between the initial and delayed uptake

Results Most of increased metabolic activity is diffuse (19/25), corresponding to opacity noted in CT. Highest increased metabolic activity (11/25) is noted at around the 16 week post radiation period; mean SUV of 3.5 was measured in the initial images and interval increase of average 15% in the delayed images. Clinically significant increased metabolic activity (SUV greater than 2.5) is noted in 9/25 patients until 6 month post radiation period.

Conclusions Increased in SUV values in delayed imaging occurs in about 50% of patients with radiation pneumonitis. Careful review of CT exam and radiation history is required for a final interpretation.