Response Adapted Therapy: Using FDG-PET after Chemotherapy in Order To Restrict Indication for Radiotherapy in Children and Adolescents with Early Stages of Hodgkin’s Lymphoma (HL).

Introduction: Radiotherapy is an important risk factor for the development of secondary malignancies in children with Hodgkin’s lymphoma. The GPOH-HD-study group tries to restrict the indication for radiotherapy after two cycles of intensive OPPA (OEPA) chemotherapy. In the GPOH-HD 95 trial 113/394 (29%) of patients with early stage HL were in complete remission (CR) after chemotherapy based on CT/MRI (=CRI) criteria. They were not irradiated and achieved an excellent 97% EFS rate at 5 yrs (Dorffel, 2003). Objective: Our next study will drop radiotherapy also in patients with residual findings according to CRI criteria if FDG-PET converts to negative after chemotherapy as ascertained by real-time central review of all images. Here we report pilot data on the conversion rate. Results: During the GPOH-HD 2002 Pilot study 41 patients with early stage HL received both a staging PET at diagnosis and a restaging PET after chemotherapy. Images were centrally reviewed in Leipzig. 7 patients were in CR based on both PET and CRI criteria, one patient with CRI-based CR had still a positive PET result; in a further patient PET was not completely evaluable. In 17/32 patients with residual masses PET was completely negative after chemotherapy. In one patient PET was completely negative except for one initially involved site, where it was not informative due to a local artefact; however, CRI showed local CR in this region. In summary, 27/41 (66%) patients would qualify for no radiotherapy within a PET-based response adaptation strategy in contrast to only 9/41 (22%) patients when CRI-based. Interestingly, in 13/17 patients with negative PET, a residual mass within the mediastinum was found, indicating that a PET-based strategy will prevent many patients from mediastinal irradiation. Conclusion: A FDG-PET-based response evaluation has the prospect to avoid radiotherapy in about 60 – 70% of all patients with early stage HL. Our next trial is designed to demonstrate that this does not lead to an unacceptable increase of the relapse rate.