Reply: Neither Posttreatment PET/CT Nor Interim PET/CT Using Deauville Criteria Predicts Outcome in Pediatric Hodgkin Lymphoma

REPLY: In reply to Adams et al., we would like to state that our study assessed the prognostic significance of interim and posttreatment PET with low-dose CT (PET/CT) in pediatric Hodgkin lymphoma in comparison to conventional imaging (1). In a disease with high cure rates, the purpose of evaluation with PET/CT is to identify high-risk patients and potentially prevent overtreatment of low-risk patients.

In our study, we found the sensitivity of posttreatment PET/CT and contrast-enhanced CT (CECT) to be equally low; however, the specificity of PET/CT was significantly high as compared with CECT (76.4% vs. 95.7%). This finding was also observed in a previously reported study by Furth et al. on pediatric Hodgkin lymphoma (2), establishing the fact that although PET/CT may not detect minimal residual disease, PET/CT can reasonably rule out active disease as compared with CECT. In our study, false-positive posttreatment findings were present in 21.8% of patients on CECT, as compared with 3.9% of patients on PET/CT; hence, PET/CT in effect may alleviate unnecessary patient anxiety about the presence of residual disease in an otherwise curable disease.

In the study cited by Adams et al. (3), the metaanalysis of the proportion of false-positive posttreatment PET/CT findings in adults with lymphoma also showed a high false-positive rate, 23.1%; however, unlike our study, comparison with conventional imaging was not done. In our study, if only posttreatment CECT had been used for response assessment, 23.6% of the patients would have required additional further evaluation with biopsy or (if biopsy was not possible) follow-up imaging to rule out disease. This percentage is higher than that for PET/CT; by use of the Deauville criteria, 5.8% of patients were PET/CT-positive after treatment. In contrast to the conclusion of Adams et al., posttreatment PET/CT can decrease unnecessary invasive procedures and patient anxiety when compared with CECT because of the better specificity of PET/CT. This observation was also reported in a cost-effectiveness analysis of posttreatment PET/CT in a study by Cerci et al. (4).

On the basis of two large studies that evaluated the role of PET/CT in Hodgkin lymphoma using the Deauville criteria, posttreatment PET/CT is more valuable in detecting primary refractory disease than in predicting relapse (5,6). In those studies, 60% of patients with positive interim PET/CT findings had primary refractory disease at the end of treatment, suggesting that PET/CT identified primary refractory disease (disease unresponsive to first-line chemotherapy) better than it identified patients with minimal residual disease who would relapse. Response to salvage chemotherapy and long-term outcome differ between these two scenarios (7). This also explains the inferior survival observed in our patients with positive PET/CT findings after treatment and underscores the utility of PET/CT in identifying primary refractory disease rather than predicting relapse.

We agree that routine use of PET/CT for response evaluation is not mandatory. However, in patients with risk factors for poor outcome and patients with a residual mass at the end of treatment, PET/CT may obviate further imaging or invasive tests if the results turn out to be negative, and if positive it may identify patients with primary refractory disease who require further evaluation.

• © 2017 by the Society of Nuclear Medicine and Molecular Imaging.