Increased ¹⁸F-deoxyglucose uptake in the lung during the first weeks of radiotherapy is correlated with subsequent Radiation-Induced Lung Toxicity (RILT): A prospective pilot study

Purpose: As Radiation-Induced Lung Toxicity (RILT) is dose-limiting for radiotherapy (RT) of lung cancer and current parameters are only moderately associated with RILT, we sought for novel parameters associated with RILT. Patients and methods: In this prospective study, FDG-PET-CT scans were taken on days 0, 7 and 14 after initiation of high-dose RT in 18 patients with stage III non-small cell lung cancer. The maximal Standardized Uptake Value (SUV_max) in the lung outside of the GTV was used as a measure of FDG uptake. At the same time-points, the serum IL-6 concentrations were measured. RILT was defined as dyspnea score ≥2 (CTCAE3.0). Results: Six of 18 patients developed RILT. Before RT, SUV_max in the lung was not significantly different between patients who developed RILT and those who did not develop RILT. Patients who developed RILT post-radiation had a significant increased SUV on days 7 and 14 during RT, whereas the group that did not experience RILT showed no significant SUV changes. The SUV_max of the lungs increased significantly more in the group that later developed RILT compared to those who did not develop RILT. Neither the IL-6 concentration nor the mean lung dose was associated with RILT. Conclusions: The increase in FDG uptake in the normal lung early during RT was highly associated with the subsequent development of clinical RILT. This may help to identify patients at high risk for RILT at a time when adjustments of the treatment or strategies to prevent RILT are still possible.