Relapse Analysis of Irradiated Patients Within the HD15 Trial of the German Hodgkin Study Group

Purpose To determine, in the setting of advanced-stage of Hodgkin lymphoma (HL), whether relapses occur in the irradiated planning target volume and whether the definition of local radiation therapy (RT) used by the German Hodgkin Study Group (GHSG) is adequate, because there is no harmonization of field and volume definitions among the large cooperative groups in the treatment of advanced-stage HL. Methods and Materials All patients with residual disease of ≥2.5 cm after multiagent chemotherapy (CTX) were evaluated using additional positron emission tomography (PET), and those with a PET-positive result were irradiated with 30 Gy to the site of residual disease. We re-evaluated all sites of disease before and after CTX, as well as the PET-positive residual tumor that was treated in all relapsed patients. Documentation of radiation therapy (RT), treatment planning procedures, and portal images were carefully analyzed and compared with the centrally recommended RT prescription. The irradiated sites were compared with sites of relapse using follow-up computed tomography scans. Results A total of 2126 patients were enrolled, and 225 patients (11%) received RT. Radiation therapy documents of 152 irradiated patients (68%) were analyzed, with 28 irradiated patients (11%) relapsing subsequently. Eleven patients (39%) had an in-field relapse, 7 patients (25%) relapsed outside the irradiated volume, and an additional 10 patients (36%) showed mixed in- and out-field relapses. Of 123 patients, 20 (16%) with adequately performed RT relapsed, compared with 7 of 29 patients (24%) with inadequate RT. Conclusions The frequency and pattern of relapses suggest that local RT to PET-positive residual disease is sufficient for patients in advanced-stage HL. Insufficient safety margins of local RT may contribute to in-field relapses.