FDGPET for the Detection of Recurrence

Although early diagnosis of relapse will lead to early administration of salvage therapy, the crucial question is whether a lesion is metabolically active, because two-thirds of patients with HD present with fibrotic or recurrent mass lesions, and 20% of these relapse.344 Fifty percent of patients with highgrade NHL present with a mass lesion and only 25% of them relapse.344 67Ga will not accurately indicate whether a tumor is metabolically active, and it has limitations in detection of intraabdominal and low-grade lymphoma.345

False-positive PET studies may be the result of FDG uptake in a hyperplastic thymus, in the gastrointestinal tract, or in an inflamed lung lesion.346 False-negative results may also arise from the absence of an FDG-avid lesion within small tumor lesions, possibly because of low glucose metabolism after therapy or acquisition problems, such as spatial resolution and partial volume effect.

The value of the sensitivity and specificity of FDG-PET and CT to predict the relapse of malignant lymphoma were described in several studies.347,348 Jerusalem et al.349 evaluated the recurrence rate in 45 NHL/HD patients with residual tumor masses and positive FDG-PET results, and it was only 26% in patients with residual tumors and negative FDG-PET results. The 1-year PFS and OS rates were 86% and 92%, respectively, for the PET-negative group, and only 0% and 55%, respectively, for the PET-positive group.

Guay et al.350 compared the diagnostic accuracy of FDG-PET and CT in detecting residual disease or relapse during the posttherapy period in 48 patients with HD. The sensitivity, specificity, PPV, and NPV of FDG-PET for predicting relapse were 79%, 97%, 92%, and 92%, respectively. The accuracy of FDG-PET was 92%, higher than the accuracy of CT (56%). Freudenberg et al.351 described the advantages of PET/CT fusion imaging in 27 patients with lymphoma and evaluated the clinical significance of combined PET/CT and compared the staging results of PET/CT with those of FDG-PET and CT alone (Table 33.15).

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