An Evaluation of the Predictive Value of Immediate Post-reatment PET/CT Scans in Pediatrics Lymphomas

Abstract

PURPOSE: Optimization of treatment is vital in pediatrics because of secondary malignancy. Very little is published about the predictability of FDG PET/CT for treatment response in pediatric lymphomas. The purpose was to evaluate the predictive value of mid-treatment 18F-Fluorodeoxyglucose (18F-FDG) PET/CT in pediatric patients with Hodgkin disease (HD) and non-Hodgkin lymphoma (NHL) for treatment response. METHOD AND MATERIALS: There were 18 patients, (age 7 to 18), followed with multiple scans,pre-treatment scan (D0), immediate post treatment (D1)-median 60days, and post-treatment (D2)median of 142 days. 89 significantly positive lesions found on D0 were followed. Two patients failed to respond. In one of those patients the second scan (D1) was more positive than the pre-treatment scan (D0), but the positivity decreased in (D2) the post treatment scan, with a modified treatment. This patient is excluded from the regression analysis, but not from the equivalence analysis. RESULTS: The linear regression characterizing the relationship between the lesions in both studies is defined by a slope of 1.28, an intercept of -0.36, and a correlation of 0.86, not significantly different from the identity. Lesions were compared in a binary way (positive>SUV=2.5). There was agreement (positive or negative) in 84% of the cases. For the response, the threshold was set at less than 30% of the original SUV value: On a patient basis the agreement is less, if the rule is that no lesion can be positive without characterizing the patient as positive: In that case there is disagreement in 33% of the patient cases. However, if response is considered (a decrease) down to 30%, the agreement is good: There is a 89% agreement on patient basis. On the basis of lesions there is a 92% agreement. CONCLUSION: The predictive value of the immeditae post treatment scan is high if SUV decreases to 30% of the max. Most responses are homogeneous amongst lesions. The SUV changes from the orgianl SUV instead of actual SUV should be used to evaluate treatment response. CLINICAL RELEVANCE/APPLICATION: The SUV changes from the orgianl SUV on pre-treatment PETCT scan instead of actual PETCT SUV should be used to evaluate treatment response.