Inferior glucose metabolism and chemosensitivity of post-radiotherapy local recurrence in comparison with distant metastases as assessed by serial 18F-FDG PET/CT imaging.

Abstract

e21004 Background: Patients locally recurring after radiotherapy have increased risk of metastatic progression. This study is to compare the glucose metabolism and chemosensitivity of recurrences and metastases in the same patient by serial FDG PET/CT imaging. Methods: The 18F-FDG PET/CT images of patients with both local recurrences and distant metastases after initial treatments (definitive radiotherapy/chemo-radiotherapy as radiation group, or radical surgery as surgery control group) were reviewed. The tumor maximal diameter on CT and PET images (DCT and DPET), maximal SUV (SUVmax), mean SUV (SUVmean) were measured. PET/CT scans were performed again within 1-4 weeks after further chemotherapy. The relative changes of DCT, DPET, SUVmax and SUVmean for each focus were calculated and compared between the recurrences and metastases for both groups. Results: In surgery group (10 patients), no significant difference was found in tumor size, FDG uptake and chemosensitivity between recurrences (20 foci) and metastases (32 foci). However, in radiation group (23 patients), both SUVmax (mean ± SE: 7.03 ± 0.46) and SUVmean (4.33 ± 0.22) of recurrences (57 foci) were lower than those (8.45 ± 0.53 and 5.36 ± 0.30, respectively, P < 0.05) of metastases (68 foci). Moreover, the response extents of recurrences (45 foci) were lower than that of metastases (46 foci), with ΔSUVmax% (-21.83 ± 6.41% vs. -44.37 ± 3.96%), ΔSUVmean% (-29.31 ± 5.68% vs. -49.93 ± 4.16%), ΔDCT% (-23.12 ± 6.43% vs. -50.45 ± 4.95%), and ΔDPET% (-21.8 ± 7.19% vs.-49.5 ± 5.49%, P < 0.05). Conclusions: The local recurrences within pre-irradiated field and distant metastases in the same patient do not share the same biological characteristics and treatment response, with the inferior glucose metabolism and chemosensitivity in local recurrent tumors.