Abstract: Objective To compare the value of 18F-FDG PET/CT performed in the interim and later phase of chemotherapy in
predicting the prognosis of diffuse large B-cell lymphoma (DLBCL). Methods 18F-FDG PET/CT was performed in 71 patients
with DLBCL in the interim phase of chemotherapy (3-4 cycles) and in another 71 patients in the later phase of chemotherapy
(5-8 cycles). The patients were followed up for an average of 28.73 months (18-114 months) to compare the progression-free
survival (PFS) and the PFS rate. Results The positive finding rate was similar between 18F-FDG PET/CT performed in the
interim and the later phase (36.6% vs 33.8%, χ²=12.423, P>0.05). The PFS was much longer in patients with negative findings
than in those with positive findings in both the interim (63.56 vs 19.23 months, P=0.000) and later phase groups (65.78 vs 24.32
months, P=0.000), but showed no significant difference between the negative patients (P>0.05) or between the positive patients
(P>0.05) in the two groups. The PFS rate was significantly greater in patients with negative than those with positive findings in
the interim group (73.3% vs 15.4%, P=0.000) and in the later phase group (74.5% vs 16.7%, P=0.000), but comparable between
the negative (P>0.05) and between the positive patients (P>0.05) in the two groups. Conclusions 18F-FDG PET/CT in the interim
and later phase of chemotherapy has similar value for predicting the prognosis of DLBCL, and we therefore recommend that
18F-FDG PET/CT be performed in the interim but not in the later phase.