Patients
The institutional review board of Sun Yet-Sun University Cancer Center approved this retrospective study. We reviewed the clinical data of eligible patients with HL who were treated at the Department of Pediatric Oncology in Sun Yet-Sun University Cancer Center between January 2008 and May 2019. Patients were eligible for analysis when they fulfilled all of the following criteria: (1) Patients were aged < 21 years and had biopsy-proven, classic HL diagnosed according to the 2008 World Health Organization classification19. (2) Staging was performed according to the baseline FDG PET/CT scan results and the Ann Arbor staging system. (3) Interim PET/CT was performed after 2 cycles of chemotherapy (4) Post-treatment PET/CT was performed at least 3 weeks after the end of chemotherapy or 6 weeks following radiotherapy. (5) Complete remission (CR) was achieved at the end of the first-line treatment based on the PET/CT scan results. (6) Complete clinical data were available, including the date of diagnosis, details of anticancer treatment, and findings of outpatient follow-up.
Exclusion criteria: (1) Patients who were adults or diagnosed with other types of lymphoma, patients without baseline or post-treatment PET/CT scans, (2)Patients with refractory HL defined as progression or new lesions on PET/CT within three months of first-line treatment20. Patients without interim PET/CT, for example, whose PET/CT was performed after 4–6 cycles of chemotherapy, were also excluded. (3) Patients without interim PET/CT, for example, whose PET/CT was performed after 4–6 cycles of chemotherapy.