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.