PET scans (know indications only)

Role

FDG-PET (typically combined PET-CT) is central to staging, treatment response assessment, and end-of-treatment evaluation in FDG-avid lymphomas (most notably Hodgkin lymphoma and diffuse large B cell lymphoma) - the specific knowledge required is indications, not detailed interpretation
Now standard of care for staging and response assessment in FDG-avid lymphoma subtypes, given its superior sensitivity over CT alone for detecting nodal and extranodal disease

Metabolically active lymphoma tissue takes up FDG preferentially, allowing whole-body assessment of disease extent and metabolic activity in a single study, complementing (and in FDG-avid lymphomas, largely superseding) CT-alone staging

Indications: initial staging of FDG-avid lymphoma (Hodgkin lymphoma, diffuse large B cell lymphoma, and other aggressive subtypes), interim response assessment during treatment (guiding treatment adaptation in some protocols), and end-of-treatment response assessment using standardised criteria (the Deauville score, a 5-point visual scale comparing residual uptake to reference structures)
Not all lymphomas are reliably FDG-avid - some indolent subtypes (e.g. some marginal zone lymphomas) show lower/inconsistent FDG uptake, making PET less reliable for staging/response assessment in these specific subtypes, where CT-based assessment remains more appropriate

A negative end-of-treatment PET (low Deauville score) supports complete metabolic response and generally correlates with good long-term outcome; a positive interim or end-of-treatment PET does not always indicate residual lymphoma (inflammatory change can also cause uptake) and may prompt biopsy confirmation before treatment escalation in ambiguous cases

Hodgkin lymphoma, diffuse large B cell lymphoma, Deauville score, indolent lymphoma subtypes with variable FDG avidity

PET-CT has become integral to modern lymphoma management specifically because response assessment now incorporates metabolic activity, not just anatomical size change - a lymph node that has shrunk on CT but remains markedly FDG-avid is treated differently from one that has both shrunk and become metabolically inactive

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