PET/CT Dual Time Point Scanning in Evaluation of Malignant Lymphoma

Purpose: The purpose of the present study is to evaluate the value of dual-time-point F-18 FDG PET/CT imaging in malignant lymphoma (ML) to differentiate between benign lesions and residual or relapsing malignant lesions. Patients and methods: This prospective study included 252 lymph nodes in 60 patients. F-18 FDG PET/CT scan was performed at 50 min (early scan) and at 100 min (delayed scan) after the injection. The maximum standardized uptake value (SUV max) of each lesion was calculated at early and delayed scans. We estimated the difference between early and delayed SUV max (D-SUV max) and the retention index (RI-SUV max) to evaluate the change of tracers handling in the lesions. Also, the early lesion/liver ratio and delayed lesion/liver ratio were calculated. Then their cut-off values were evaluated using receiver operating characteristic analysis. Correlations of these cutoff values with different clinico-pathological parameters were done. Results: The cut-off value in Early-SUV max was 4.05, Delayed-SUV max were 4.45, D-SUV max was 0.45, RISUV max was 0.155, Early lesion/liver ratio was 1.25 and in Delayed lesion/liver ratio was 1.35. The delayed-SUV max had the highest sensitivity and specificity of 85.3% and 92.6% respectively. The overall result of DTP PET/CT showed sensitivity of 95.3%, specificity of 76.4%, accuracy of 86.1%, and positive predictive value of 80.9% and negative predictive value of 94% respectively. Based on a total of true and false results in early and delayed PET/CT imaging, there was significant improvement in specificity in the delayed PET/CT imaging compared to the early PET/CT imaging. Correlation of DTP cut off value with the different clinico-pathological parameters showed that nodular sclerosis and lymphocytic predominance pathological subtypes had the highest sensitivity of 100%, while mixed cellularity showed the lowest sensitivity of 64.3%. In Hodgkin lymphoma lesions, cervical sites showed Egyptian J. Nucl. Med. Vol 12, No 2 December 2015 P a g e | 11 the lowest sensitivity and specificity 90.2% & 61.4% respectively. Conclusions: The dual time point FDG PET/CT scan is useful to differentiate between post-therapy changes as benign lesions and residual or relapsing malignant lesions in malignant lymphoma.