PET-CT for Lymphoma: — Hodgkin, Non-Hodgkin, and the Subtypes That Matter

A Deauville 3 means uptake above background but no higher than liver — which sits in the middle of the scale. Whether that is reassuring or concerning depends on the type of lymphoma, where you are in treatment, and the protocol your team is following. In some contexts a 3 is treated as a response; in others it prompts a change in approach. Never interpret a Deauville score on its own. Your haemato-oncologist applies it alongside your full clinical picture, and that conversation is the right place to ask what it means for you.

Yes, in certain subtypes. Low-grade lymphomas — follicular, marginal zone, small lymphocytic — often have low or absent FDG uptake, so PET can appear normal even when significant disease is present. Your team accounts for this by using CT alongside, or by not relying on PET for those subtypes at all. In FDG-avid lymphomas like Hodgkin or DLBCL, a missed area of disease is much less common, though no scan is entirely perfect.

A baseline scan is done before treatment starts and gives a reference point for every scan that follows. Without it, it is harder to say whether a finding on a later scan is new or was already there. In lymphoma, the baseline also confirms whether your specific disease is FDG-avid — which matters because low-grade subtypes are variable. If you have not had a pre-treatment scan, ask your team whether one should be done before you begin.

Transformation means a low-grade lymphoma has changed into an aggressive subtype. The transformed area takes up far more FDG than the surrounding disease and appears on PET as a new bright focal area against a background of otherwise faint or absent uptake. If your report describes markedly increased uptake in a single site within a previously low-grade disease, that language is often the radiologist flagging possible transformation. A biopsy of that site is needed to confirm it.

The choice depends on your subtype and what the scan is looking for. In Hodgkin lymphoma and DLBCL, PET detects active metabolic disease and is the preferred response assessment tool. In low-grade lymphomas, CT is often preferred for measuring lymph node size over time, because PET uptake is too low to be reliable. Some protocols use both. Your treating team follows the guidance relevant to your specific diagnosis — if you are unsure which approach applies to you, asking at your next appointment is straightforward.

CION coordinates PET-CT through partner imaging centres. Your haemato-oncologist orders the scan and receives the report directly. The appointment is done on an outpatient basis and does not require a hospital stay. The team at your CION centre will tell you where to go, how to prepare — including fasting instructions — and what to expect on the day.