Changes in plasma transforming growth factor beta during radiotherapy and the risk of symptomatic radiation-induced pneumonitis

Purpose: To determine whether changes in the plasma Transforming Growth Factor β1 (TGFβ1) concentration during radiotherapy could identify patients at risk for developing symptomatic radiation pneumonitis. Methods and Materials: Thirty-six patients who received radiation therapy with curative intent for lung cancer (n = 31), Hodgkin's disease (n = 4), or thymoma (n = 1) were evaluated prospectively. All patients had serial plasma TGFβ1 measurements obtained before, during, and after treatment. Plasma TGFβ1 was quantified using an enzyme-linked immunosorbent assay. Pneumonitis was defined clinically. Plasma TGFβ1 levels were considered to have normalized if the following occurred: the last on-treatment TGFβ1 level was both <7.5 ng/ml and lower than the pretreatment level. Results: Thirteen of these 36 patients developed pneumonitis. Significant changes in plasma TGFβ1 levels during treatment were seen only in the subset of patients whose TGFβ1 levels were >7.5 ng/ml at baseline (n = 22). Failure of plasma TGFβ1 to normalize by the end of treatment, as defined above, much more accurately identified patients at risk for symptomatic pneumonitis if their baseline TGFβ1 was >7.5 ng/ml than if it was <7.5 ng/ml. Conclusions: Changes in plasma TGFβ1 levels during radiotherapy appears to be a useful means by which to identify patients at risk for the development of symptomatic radiation pneumonitis, particularly in the subset of patients whose pretreatment TGFβ1 levels are >7.5 ng/ml.