PET/CT is a fusion technique of Positron Emission Tomography (PET) and CT, which in short means adding functional imaging to CT imaging. What does it mean? For example, in the era of CT, we could only determine whether a lymph node was malignant by its size, shape, blood supply, margins, etc., but if we can add PET, we can see whether the metabolism of the lymph node is elevated (malignant tumors are characterized by a significant increase in glucose metabolism), and we can detect some small lesions. Thus PET/CT has two important roles in Hodgkin’s lymphoma (HL). 1. More accurate staging. The sensitivity of PET-CT is reported to be 92% for lymph node lesions and 83% for CT, while for extra-nodal lesions, the sensitivity of PET-CT is 86% and CT is 37%, respectively. PET-CT eventually changed the treatment plan in about 9% of patients because the disease stage was affected. If the patient has already had a whole-body PET-CT scan, further diagnostic CT may be unnecessary. 2. Evaluate the efficacy to guide the follow-up treatment and determine the prognosis. It has been found that the progression recurrence rate of positive patients who underwent PET-CT scan after 1-2 cycles of chemotherapy for HL was 27% compared to 2.3% for negative patients, and patients with ABVD who were still positive after 2 cycles could have a higher CR rate if they switched to BEACOPP. Therefore, the guidelines recommend PET-CT at the midpoint of treatment for classical Hodgkin lymphoma (CHL) to help determine the next step in treatment, including local radiotherapy. In contrast, for nodular lymphocyte-dominant Hodgkin lymphoma (LPHL) most of which may be overstaged due to positive PET, the guidelines do not recommend PET-CT for restaging of LPHL. Patients undergo PET-CT scans at the end of all treatments to evaluate the presence of residual lesions, and biopsies may be taken again for positive lesions. However, PET-CT is not recommended as a follow-up examination for HL.