Athough CT remains the gold standard for the staging and follow-up of malignant lymphomas, 18F-FDG PET has a potential role in accurately staging disease and in predicting response to therapy. On the other, guidelines do not recommend MRI for surveillance. The most common lymphoma is Diffuse Large B0cell Lymphoma(DLBCL). 2012 NCCN Guidelines for DLBCL on p. BCEL-4 recommend CT no more often than every 6 months for 2 years after completion of treatment, then only as clinically indicated. In contrast to the North American guidelines, the European Society of Medical Oncology (ESMO) in 2007 specifically advises against routine imaging except to evaluate residual disease. These guidelines recommend:
PET scan at end of treatment, if available
Minimal radiologic examinations in patients with DLBCL at 6, 12, and 24 months after end of treatment, when indicated by site of disease
In regard to followup, a recent study showed that a negative PET scan after completion of therapy does not exclude the presence of residual microscopic disease and does not indicate complete remission. The majority of studies evaluating FDG-PET in lymphoma include patients with diffuse large B-cell non-Hodgkin’s lymphoma (NHL) or Hodgkin’s disease. There are limited data available on the role of PET in other histologies.
A negative PET scan at the end of therapy appears to provide favorable prognostic information. Persistently positive PET scans at the end of therapy, or in follow-up, warrant close follow-up or additional diagnostic procedures, since some of those patients may remain in prolonged remission.
The Imaging Subcommittee of the International Harmonization Project (IHP) in Lymphoma developed guidelines for performing and interpreting positron emission tomography (PET) for treatment assessment in patients with lymphoma. The new recommendations, targeting both clinical practice and clinical trials, are published in the January 22 Early Release issue of the 2007 al of Clinical Oncology. They are based on experts’ consensus and not randomized evidence.
Specific recommendations related to followup are:
After treatment completion, PET should be performed at least 3 weeks, and preferably 6 to 8 weeks, after chemotherapy or chemoimmunotherapy, and 8 to 12 weeks after radiation or chemoradiotherapy. Noncontrast PET/CT can be used instead of contrast-enhanced diagnostic CT to follow-up patients with lymphoma, although patients with hepatic or splenic involvement should continue to receive contrast-enhanced diagnostic CT. Attenuation-corrected PET is much preferred over nonattenuation-corrected scans.
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