Comparative Assessment of Different Criteria for Interim-PET Interpretation in a Cohort of Hodgkin Lymphoma Patients Treated in a Single Center.

Interim-PET scan performed early during treatment is the most important prognostic factor in Hodgkin lymphoma (HL). However, simple reproducible criteria for scan interpretation are lacking and still await standardization.

To evaluate in a cohort of ABVD-treated HL patients in a single centre the overall accuracy of different criteria of interim PET interpretation in which interim scan was not decisional for treatment change.

From December 2003 till June 2008, 75 HL patients were consecutively admitted to hematology department of Santa Croce Hospital in Cuneo. Baseline and interim-PET (PET-2) scans were performed with a PET/CT equipment. Limited-stage patients (I-IIA) were treated with ABVD x 3-4 plus Involved-field radiotherapy; advanced-stage (IIB-IVB) patients with ABVD x 6 plus consolidation radiotherapy on bulky disease. The injected dose was 370 MBq/70 kg. 2D images were acquired a mean of 71 (47-122) minutes after Fluorodeoxyglucose (FDG) injection. Images were reconstructed with OSEM (3 iteration, 26 subsets). PET-2 was performed after a median of 11(8-13) days from 2nd ABVD end, and no treatment change was allowed based on PET-2 results. Two expert nuclear medicine physicians independently interpreted the PET-2 scans and jointly reviewed the discordant cases. Six interpretation criteria on the basis of literature reports were used: three qualitative, two quantitative, based on Standardized Uptake Value (SUV) assessment, and one with a qualitative/dimensional approach, with a dimensional cutoff value for FDG correction of 15 mm.: Juweid 2007 (Ju), Gallamini 2007 (Ga), Barrington 2008 (Ba) for qualitative, SUVmax determination, SUVmax variation (deltaSUV) for quantitative, and Barrington + dimensional (Ba/d) for a qualitative/dimensional approach.

Clinical characteristics of the patients were: mean age 33 (14 - 73), male sex 39/75, limited vs. advanced stage 37/38, International Prognostic Score (IPS), (in 69/75 patients) was 0 in 17,1 in 19, 2 in 19, 3 in 8, 4 in 5, 5-7 in 1 patients. After a mean follow-up of 937 days 67 patients are in CR, and 8 experienced treatment failure, three of them have died. In case of residual FDG uptake the mean diameter of the persisting lesion was 19.9 mm. Overall, 2/8 patients with treatment failure (True PET-2+) and all the 9 patients with false+ or false- PET-2 (whatever criteria) showed a persistent FDG uptake in a single lesion, with a median diameter of 14 millimetres. Sensitivity and specificity, were:100%,70%, for Ju; 63%, 87% for Ga; 63%, 91% for Ba; 75%, 93% for SUVmax; 50%, 94% for deltaSUV; 89%, 89% for Ba/d. Among the qualitative assays Ba and Ba/d showed the best results. The latter were equivalent to both quantitative assay. Using the Ba /d score 8 patients showed false-positive scans: 6/8 with stage IIA and 7/8 with bulky disease, and the 3-year failure-free survival for the entire cohort and for advanced-stage patients were 98%, 53% and 96% and 25% for PET-2 negative and positive patients, respectively.

This study suggest that (1) the criteria of the Harmonization Study for end-treatment evaluation of response should not be used for PET-2 interpretation (2) the lower performance of qualitative in respect to the quantitative criteria is offset by the adjunction of dimensional parameters; (3) due to the small size of the residual lesion with a persistent FDG avidity in PET-2, the contribute of the dimensional criteria could sensibly improve the performance of qualitative criteria, such as Ba, that are currently used for multicenter clinical trials.

No relevant conflicts of interest to declare.