ICML Imaging Working Group Issues Updated Guidelines on PET-CT for Staging and Response Assessment for FDG-Avid Lymphomas


Key Points

  • Staging and assessment of FDG-avid lymphomas is recommended using visual assessment, and a 5-point scale is recommended for reporting PET-CT.
  • PET-CT is recommended for midtherapy assessment in place of CT alone, if imaging is indicated, and for remission assessment.

Barrington et al in the International Conference on Malignant Lymphomas Imaging Working Group have presented updated consensus guidelines on 18F-fluorodeoxyglucose (FDG) positron-emission tomography (PET)-computed tomography (CT) for staging and response assessment for FDG-avid lymphomas. The guidelines are published in the Journal of Clinical Oncology

The imaging working group comprises representatives from major international cooperative groups, who reviewed the literature, communicated information on research in progress, and identified key areas in research in imaging and lymphoma. A working paper was circulated for comment and presented at the Fourth International Workshop on PET in Lymphoma in Menton, France, and at the 12th International Conference on Malignant Lymphomas in Lugano, Switzerland, to update the International Harmonisation Project guidance regarding PET. The updated recommendations, summarized below, are intended to optimize use of PET-CT in staging and response assessment in clinical practice and late-phase clinical trials.

Interpretation of PET-CT Scans

  • Staging of FDG-avid lymphomas is recommended using visual assessment, with PET-CT images scaled to the fixed standardized uptake value (SUV) display and color table; focal uptake in Hodgkin lymphoma and aggressive non-Hodgkin lymphoma is sensitive for bone marrow involvement and may obviate the need for biopsy; magnetic resonance imaging is the modality of choice for suspected CNS lymphoma.
  • The 5-point scale is recommended for reporting PET-CT; scores of 1 and 2 represent complete metabolic response; a score of 3 also probably represents complete metabolic response in patients receiving standard treatment.
  • A score of 4 or 5 with reduced uptake from baseline probably represents partial metabolic response, but indicates residual metabolic disease at the end of treatment; an increase in FDG uptake to score 5, score 5 with no decrease in uptake, and new FDG-avid foci consistent with lymphoma represent treatment failure or progression.

PET-CT for Staging

  • PET-CT should be used for staging in clinical practice and clinical trials, but is not recommended for routine use in lymphomas with low FDG avidity; PET-CT may be used to select optimal biopsy site.
  • When used at staging or restaging, contrast-enhanced CT should ideally be performed during a single visit combined with PET-CT; findings will determine whether contrast-enhanced PET-CT or lower-dose unenhanced PET-CT is sufficient for additional imaging.
  • Volumetric measurement of tumor bulk and total tumor burden, including methods combining metabolic activity and anatomical size or volume, should be explored for potential prognostic information.

Interim PET

  • PET-CT is superior to CT alone in assessing early response in midtherapy imaging; the role of PET response-adapted therapy is currently being investigated in clinical trials; currently, it is not recommended that treatment be changed solely on the basis of interim PET-CT unless there is clear evidence of progression.
  • Standardization of PET methods is mandatory for use of quantitative approaches and desirable for routine clinical practice.
  • Data suggest that quantitative measures (eg, δSUVmax) may improve on visual analysis for response assessment in diffuse large B-cell lymphoma, but this requires further validation in clinical trials.

PET at End of Treatment

  • PET-CT is to be used for remission assessment in FDG-avid lymphoma; biopsy is recommended when salvage treatment is considered in the presence of residual metabolically active tissue.
  • Data on significance of PET-negative residual masses should be collected prospectively in clinical trials; residual mass size and location should be recorded on end-of-treatment PET-CT reports when possible.
  • Emerging data support use of PET-CT after rituximab-containing chemotherapy in follicular lymphoma with high tumor burden; confirmatory studies are warranted in patients receiving maintenance therapy.
  • PET-CT could be used to guide decisions before high-dose chemotherapy and autologous stem cell transplantation, but additional studies are warranted.

Sally F. Barrington, MBBS, MSc, MD, Reader in Nuclear Medicine, of the PET Imaging Centre at St Thomas’, London, is the corresponding author for the Journal of Clinical Oncology article.

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