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  Objective  To assess the staging, restaging, and treatment strategy determination of extranodal NK/T cell lymphoma (ENKT) by PET/CT real body (true whole-body, TWB) imaging, which is superior to PET/CT limitation of the whole body (limited whole-body, LWB, from skull vertex to upper thighs) by adding ‘distal lower extremity’ images.

  Methods  TWB ¹⁸F-FDG PET/CT studies performed for staging and follow-up of ENKTL patients between January 2012 and September 2017 were retrospectively reviewed. Patients in staging group received TWB PET/CT evaluation for staging at the first diagnosis. In follow-up group, patients received follow-up evalution with TWB PET/CT and progressive disease (PD) in the LWB range with or without clinical diagnosis or suspicion before follow-up examination, and then divided into four subgroups: staging (+) PD (－), staging (+) PD (+), staging (－) PD (－), staging (－) PD (+). Then the percentage of unexpected ENKTL lesions found at the distal extremity (outside the LWB range) (P1), and the percentage of changes in the staging, restaging/outcome evaluation (P2) in each group were recorded.

  Results   Among the 225 patients in the staging group, 200 (88.9%) had tumors confined to LWB, while P1 was 11.1% (25 cases) and P2 was 0.4% (1 case). In the follow-up group, the P1 in staging (+) PD (－)(n=85), staging (+) PD (+)(n=4), staging (－) PD (－)(n=43), staging (－) PD (+) goups (n=15) were 1.2%, 75.0%, 0%, 26.7%, and P2 were 1.2%, 0%, 0%, 13.3%, respectively. In the follow-up group, regardless of whether the TWB PET/CT examination was performed at the initial diagnosis stage, P1 in PD (－) group and PD (+) group was 0.8 vs. 36.8% (P<0.000 1), and P2 was 0.8% vs. 10.5% (P<0.000 1).

  Conclusion  It is not recommended that the TWB PET/CT imaging from the top of the head to the bottom of the foot use for the first diagnosis of ENKTL patients. And for follow-up patients with no clinical evidence of tumor progression or with evidence of tumor progression but whose lesions were limited to LWB at the initial diagnosis of TWB PET/CT staging, LWB PET/CT from the top of the head to the middle of the thigh is recommended for routine follow-up. For ENKTL patients, TWB PET/CT was not performed at the initial stage of diagnosis to detect the condition of lower limbs. If the evidence of tumor progression in the LWB range appeared before the follow-up examination, TWB PET/CT was recommended for the follow-up evaluation to evaluate the systemic tumor involvement.