Quantitative assessment of interim PET in Hodgkin lymphoma An evaluation of the qPET method in adult patients in the RAPID trial

140 Aim: The Deauville score (DS) is used for response assessment of FDG-PET scans in Hodgkin lymphoma (HL). qPET has been proposed as a quantitative extension to the DS, extending the ordinal DS (scores 1-5) into a continuous scale (1). qPET is the ratio of the peak standardised uptake value (SUV) in the site of highest residual uptake over the mean SUV in the liver. qPET was developed using scans from 898 paediatric HL patients treated in the EuroNet-PHL-C1 (C1) trial. The aim of this study was to determine if qPET could be applied as an alternative method to assess response in adult patients in the RAPID Trial (2). Methods: PET-CT scans performed after 3 cycles of Adriamycin, Bleomycin, Vinblastine and Dacarbazine (ABVD) in patients from RAPID were re-evaluated by an independent reader, blinded to PET results in the trial and patient outcome. All initially involved regions were assessed visually using the DS and measured using the qPET method. The distribution of qPET measurements was compared for RAPID and C1 patients. Previously published qPET thresholds which correspond to visual Deauville scores of 1-5 in C1 were used to derive quantitative Deauville scores for RAPID patients. The concordance rate between visual and quantitative DS was measured. Results: PET-CT scans were available for 450 patients from RAPID. The visual assessment showed a DS of 1 (171 scans), 2 (153 scans), 3 (72 scans), 4 (31 scans) and 5 (23 scans). The distribution of qPET values in RAPID was similar to C1 patients, with a unimodal ‘normal’ distribution (mode = 0.95) and a long tail to the right, suggestive of a favourable response in the majority and a less favourable response in the minority with outlying values. qPET thresholds derived in C1 and applied in RAPID showed 86% concordance between visual and quantitative scores of 1 -5. There was 97% concordance for complete metabolic response (CMR; DS 1-3) vs. no CMR using the Lugano classification. Conclusions: qPET which was developed in paediatric HL patients receiving more intensive Vincristine, Etoposide, Prednisone and Adriamycin (OEPA) chemotherapy, was a suitable quantitative method for assessing response in adult HL patients treated with ABVD in a response-adapted setting in the RAPID trial.