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.