Changes in glucose metabolism during and after radiotherapy in non-small cell lung cancer.

Aims and background. Evaluation of the metabolic response to radiotherapy in non-small cell lung cancer patients is commonly performed about three months after the end of radiotherapy. The aim of the present study was to assess with positron emission tomography/computed tomography (PET/CT) and [ 18 F]fluorodeoxyglucose changes in glucose metabolism during and after radiotherapy in non-small cell lung cancer patients. Methods and study design. In 6 patients, PET/CT scans with [ 18 F]fluorodeoxyglucose were performed before (PET 0 ), during (PET 1 ; at a median of 14 days before the end of radiotherapy) and after the end of radiotherapy (PET 2 and PET 3 , at a median of 28 and 93 days, respectively). The metabolic response was scored according to visual and semiquantitative criteria. Results. Standardize maximum uptake at PET 1 (7.9 ± 4.8), PET 2 (5.1 ± 4.1) and PET 3 (2.7 ± 3.1) were all significantly (P <0.05; ANOVA repeated measures) lower than at PET 0 (16.1 ± 10.1). Standardized maximum uptake at PET 1 was significantly higher than at both PET 2 and PET 3 . There were no significant differences in SUV max between PET 2 and PET 3 . PET 3 identified 4 complete and 2 partial metabolic responses, whereas PET 1 identified 6 partial metabolic responses. Radiotherapy-induced increased [ 18 F] fluorodeoxyglucose uptake could be visually distinguished from tumor uptake based on PET/CT integration and was less frequent at PET 1 (n = 2) than at PET 3 (n = 6). Conclusions. In non-small cell lung cancer, radiotherapy induces a progressive decrease in glucose metabolism that is greater 3 months after the end of treatment but can be detected during the treatment itself. Glucose avid, radiotherapy-induced inflammation is more evident after the end of radiotherapy than during radiotherapy and does not preclude the interpretation of [ 18 F]fluorodeoxyglucose images, particularly when using PET/CT.