Positron Emission Tomography Combined with Computed Tomography (PET-CT) Should Substitute Classical CT in the Initial Staging of Hodgkin Lymphoma (HL).

Disease stage remains the most powerful prognostic factor in HL and guides optimal therapy. Despite high (18)F-FDG avidity in HL, PET-CT is not mandatory in the initial staging of HL. To establish if PET-CT should substitute classical CT in the initial staging of HL we evaluate the influence (18)F-FDG PET-CT on HL stage migration and its impact on treatment selection.

96 HL patients (pts) underwent conventional CT and PET-CT staging with a median time 19 days between two tests; the stage of HL was defined separately based on CT or PET-CT results that were read afresh independently by the radiologist and the nuclear medicine specialist. The number of nodal areas and extranodal sites involved, detected by each imaging modality were scored and compared. In CT assessment, classical radiologic criteria were used. Lymph nodes >15mm in longest dimension were considered pathological. In PET-CT assessment sites of nonphysiological uptake above background were reported as pathologically involved. Focal uptake in the spleen, liver and bones/bone marrow (BM) was treated as indicative of HL involvement. Diffuse uptake in the spleen was also assumed to be indicative of HL involvement if the uptake was greater than the liver uptake. In contrast diffuse uptake in the BM even if higher than the liver was conservatively not treated as HL infiltration.

The number of patients in stage I, II, III, IV was 5, 49, 28, 14 using CT and 7, 37, 22, 30 using PET-CT. In 33 (34%) patients PET-CT changed HL stage, specifically 27 (28%) pts were upstaged whereas 6 (6,3%) pts were downstaged compared to CT results. As a consequence 20 (21%) patients required treatment modification: reduction in 4 pts and intensification in 16 pts. All 4 patients with treatment reduction had CT stage III, most (3 pts) were without B symptom. The stage was reduced due to lack of (18)F-FDG uptake in increased (>15mm) single nodes on the other site of diaphragm. All 16 pts with treatment intensification had CT stage II and two third suffered from B symptoms. The stage was upgraded mainly to the extranodal involvements (47 sites in 26 pts) detected by PET-CT that were not seen on conventional CT. Among them the most often was bone marrow (10 pts), following by spleen (5pts) and lung (2pts) involvement. In 9 pts two or more coexisting locations were detected. Extended nodal involvement seen in PET-CT compared to CT resulted in upstage only in one patient despite detection of more nodal areas compared to CT; Depending on location, 36–56% of these nodes were smaller than 15mm in greatest dimension. Moreover, PET-CT helped to define atypically located small nodes in 25 patients; in 7 of them radiotherapy was a part of radical treatment and the omission of PET-CT could have resulted in a geographical miss. BM biopsy was positive in 3 of 96 pts; in all cases PET-CT revealed diffuse BM uptake higher than the liver uptake.

The addition of PET-CT in the initial staging of HL modifies the disease stage in a significant proportion of patients, leading to treatment modification in majority of them. The impact of PET-CT on staging is of special significance in patients with CT stage II especially with B symptoms.

No relevant conflicts of interest to declare.