18 F-FDG PET/CT analysis
All 18F-FDG PET/CT analyses and reviews were performed
by two experienced nuclear medicine physicians who had access to the
results of previous imaging and clinical information, but were unaware
of the follow-up results. Interim and post-treatment PET/CT scans were
analyzed using the IHPC and DC. According to the IHPC, a PET/CT scan was
considered positive if a residual mass had a greatest transverse
diameter of >2 cm and showed more intense residual uptake
than the mediastinal blood pool activity. A smaller residual lesion or a
normal-sized lymph node was also considered positive if its activity was
above that of the surrounding background. Other criteria for defining
PET positivity in the spleen, liver, lungs, and bone marrow were
consistent with the established IHPC. According to the DC, PET/CT scans
were assigned scores on a 5-point scale as follows: no residual uptake,
1 point; residual uptake less than or equal to the mediastinum, 2
points; residual uptake greater than the mediastinum but less than the
liver, 3 points; residual uptake moderately higher than the liver, 4
points; and
residual
uptake markedly higher than the liver or the presence of new sites of
uptake, 5 points. Two separate cutoffs were used for the DC scores. With
a cutoff of 3 points (the DC-3 model), DC scores of 3–5 were considered
positive, whereas scores of 1–2
were considered negative. With a
cutoff of 4 points (DC-4), DC scores of 4–5 were considered positive,
whereas scores of 1–3 were considered negative.