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

Purpose To compare glucose metabolism and chemosensitivity between recurrence within the irradiation field and metastases outside the irradiation field in the same patient using 18 F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography images (PET/CT). Methods The 18 F-FDG PET/CT images of 43 cancer patients with both local recurrence (in-field) and distal metastases (out-field) after initial treatments were reviewed. 23 patients after definitive radiotherapy/chemoradiotherapy and 20 patients after radical surgery were assigned to a radiation group and surgery group, respectively. The tumor maximal diameter on CT and PET images ( D CT and D PET ), maximal SUV (SUV max ), and mean SUV (SUV mean ) were measured. All the patients were administered chemotherapy, and 17 patients from the radiation group and 10 patients from the surgery group underwent PET/CT scanning within 1–2 months after the treatment. The changes in D CT , D PET , SUV max and SUV mean for each lesion were calculated and compared between in-field and out-field tumors for both groups. Results In the surgery group, no significant difference was found in tumor size or FDG uptake between the local recurrence and metastases. In the radiation group, both SUV max (7.03 ± 3.48) and SUV mean (4.33 ± 1.67) of the in-field tumors were lower than those (8.45 ± 4.34 and 5.36 ± 2.51, respectively, P < 0.05) of out-field tumors. Moreover, the response extent of in-field tumors was lower than that of out-field tumors in the radiation group ( P < 0.05). However, in the surgery group, there was no difference in the response extent (tumor size and SUVs) between the local recurrence and metastases ( P > 0.05). Conclusion The recurrence within the irradiation field and metastases outside the irradiation field in the same patient do not share the same biological characteristics or treatment response, with inferior glucose metabolism and chemosensitivity seen in locally recurrent tumors.