Is contrast material needed after treatment of malignant lymphoma in positron emission tomography/computed tomography?

Purpose: Positron emission tomography (PET)/computed tomography (CT) with (18)F-fluorodeoxyglucose is widely used for post-therapeutic surveillance of malignant lymphoma. Debate still exists as to whether intravenous contrast media during the CT stage of a PET/CT scan should be used. The purpose of this study was to investigate the clinical value of contrast agent in PET/CT in patients with lymphoma following treatment.

Patients And Methods: One hundred and twenty-two consecutive patients with malignant lymphoma underwent 146 PET/CT scans to monitor therapeutic response (n = 57) or surveillance during follow-up (n = 89). All patients had a conventional PET/CT scan with low-dose CT without contrast (ldCT), and then a full-dose CT scan with contrast (ceCT). Two datasets were interpreted separately and prevalence of discrepant results between the two methods was evaluated. In addition, differences of diagnostic performance were investigated for restaging.

Results: Both PET + ldCT and PET + ceCT were positive in 22 cases and negative in 35 cases when monitoring response to therapy. There were no cases in which these techniques demonstrated inconsistent findings. For restaging, the patient-based sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy of PET + ldCT were 70, 91, 76, 87, and 84%, respectively, and those of PET + ceCT were 74, 92, 81, 89, and 87%, respectively. Discrepant results between the two methods occurred in only 2 of 89 cases (2%).

Conclusion: PET/ceCT yielded more accurate findings than PET/ldCT in a limited number of cases. PET/ldCT may, therefore, be sufficient for routine PET/CT scanning for post-therapeutic assessment or restaging of lymphoma patients.