Background: To evaluate the metabolic changes on 18 F-fluoro-2-deoxyglucose positron emissiontomography integrated with computed tomography (18 F-FDG PET-CT) performed before,during and after concurrent chemo-radiotherapy in patients with locally advanced non-smallcell lung cancer (NSCLC); to correlate the metabolic response with the delivered radiationdose and with the clinical outcome. Methods: Twenty-five NSCLC patients candidates for concurrent chemo-radiotherapy underwent 18 FFDGPET-CT before treatment (pre-RT PET-CT), during the third week (during-RT PETCT)of chemo-radiotherapy, and 4 weeks from the end of chemo-radiotherapy (post-RT PETCT).The parameters evaluated were: the maximum standardized uptake value (SUVmax) ofthe primary tumor, the SUVmax of the lymph nodes, and the Metabolic Tumor Volume(MTV). Results: SUVmax of the tumor and MTV significantly (p=0.0001, p=0.002, respectively) decreasedearlier during the third week of chemo-radiotherapy, with a further reduction 4 weeks fromthe end of treatment (p<0.0000, p<0.0002, respectively). SUVmax of lymph nodes showed atrend towards a reduction during chemo-radiotherapy (p=0.06) and decreased significantly(p=0.0006) at the end of treatment. There was a significant correlation (r=0.53, p=0.001)between SUVmax of the tumor measured at during-RT PET-CT and the total dose ofradiotherapy reached at the moment of the scan. Disease progression free survival wassignificantly (p=0.01) longer in patients with complete metabolic response measured at post-RT PET-CT. Conclusions: In patients with locally advanced NSCLC, 18 F-FDG PET-CT performed during and aftertreatment allows early metabolic modifications to be detected, and for this SUVmax is themore sensitive parameter. Further studies are needed to investigate the correlation betweenthe metabolic modifications during therapy and the clinical outcome in order to optimize thetherapeutic strategy. Since the metabolic activity during chemo-radiotherapy correlates withthe cumulative dose of fractionated radiotherapy delivered at the moment of the scan, specialattention should be paid to methodological aspects, such as the radiation dose reached at thetime of PET.
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