Рентгенология & Радиология, 2016, LV 12-16

Positron emission tomography/computer  tomography (PET/CT) in radiation pneumonitis

A. Demirev, I. Gabrovski, I. Kostadinova, V. Stoinova
Abstract.

Radiation Pneumonitis (RP) is an adverse complication of radiotherapy (RT) and can sometimes 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, respectively in about 5–50%, 5–10%, and 1–5% of all cases. PET/CT with 18F – FDG hybrid imaging 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. The current study included 23 patients (out of 220 patients with RT of the thoracic cavity and parenchyma of the lungs) examined between 2012 and 2015, who had metabolic (PET) and morphological (CT) changes consistent with RP. We additionally defined the metabolic activity or the maximum standardized uptake value (SUVmax) in the lung parenchyma of 20 patients without RT. In our patient group 13/23 of the patients had serial examinations – 9/13 before and after RT, 4/13 more than 6 months after RT. The rest of the patients 10/13 had a single examination up to 6 months / more than 6 months after RT. All patients had considerably increased metabolic activity or a tendency towards increased metabolic activity in the lung parenchyma involved in the irradiated area with a mean of SUVmax 3.45 (ranging between 1 and 7.1). The control group had a physiological background metabolic activity of respectively SUVmax 0.61 +/- 0.11. The difference in the metabolic activity between the two groups was statistically significant (p <0.0001). The particular metabolic changes in the patients suspicious of RP involved diffusely increased metabolic activity coinciding with the morphological changes in the irradiated area. 3/23 patients had a proven recurrenceof 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.

Key words: PET/CT. RADIATION PNEUMONITIS