Pediatric Hodgkin Lymphoma: visual and semiquantitative analysis of interim 18FDG-PET/CT in predicting treatment response and outcome

Background and aim: Interim 18FDG-PET/CT (PET-2) helps predict outcome and tailor treatment in adults with Hodgkin Lymphoma (HL). In contrast, PET-2 data on pediatric HL are rare, with discordant results. Visual analysis using Deauville Score (DS) was proposed to assess PET response. However a 5-point scale did not preclude inter-observer reproducibility issues. Alternative approaches were developed to improve the accuracy and reproducibility of PET-2, mainly based on PET semiquantitative parameters. We investigated the clinical usefulness of PET-2, evaluating both visual and semiquantitative analysis, in pediatric HL patients referred to a single center study. Materials and Methods: 18FDGPET/ CT was performed in 27 HL patients (age ≤16; average age: 12.8; 15 male:12 female) at baseline (PET-0), after 2 cycles of chemotherapy (PET-2) and at the end of treatment. PET response assessment was carried visually according to the DS, as well as semiquantitatively by use of absolute decrease in semiquantitative parameters from PET-0 to PET-2 (ΔsumSUVmax0-2, ΔΣSUVmean0-2, ΔΣMTV0-2, ΔΣTLG0-2) and the corresponding Response Indexes (RI%ΣSUVmax0-2, RI%ΣSUVmean0-2, RI%ΣMTV0-2, RI%ΣTLG0-2). Clinical response assessment was performed according the Cheson’s Revised Response Criteria considering patients as responders (R) or non-responders (NR). Mean follow up was 23.3 months. T-student test for unpaired groups was performed to compare PET semiquantitative parameters between R and NR. Chi-square and Fisher exact test were performed to evaluate the association among categorical variables. The prognostic capability of 18FDG-PET/CT was calculated by ROC analysis and expressed as area under curve (AUC).Results: 5/27 (18%) patients were NR at the end of therapy based on clinical outcome and, among them, 2 became R in follow-up; another one remained NR while other two died. Visual assessment was: DS=1 in 14/27 (52%), DS=2 in 1/27 (3%), DS=3 in 4/27 (15%), DS=4 in 8/27 (30%) patients. Differences between R and NR were statistically significant for ΔΣSUVmax0-2 (t=2.45, p=0.026) and almost statistically significant for ΔΣSUVmean0-2 (t=1.88, p=0.071). No significant difference was found for the other parameters. Any association among Deauville evaluation and outcome at the end of therapy was found (Fisher exact test p=0.136). The better AUCs resulted for ΔΣSUVmax0-2 (0.836; cut-off<12.5, sensitivity 80%, specificity 91%). Conclusions: Semiquantitative analysis seems to be more accurate than visual analysis to interpret PET-2 and predict outcome in pediatric HL patients. In particular, ΔΣSUVmax0-2 appears to be the best PET parameters in predicting therapy response assessment in pediatric HL patients. The integration of ΔΣSUVmax0-2 with DS, could achieve to the best PET-2 performance.