Abstract P086

TRIAL IN PROGRESS: PRIORITY (PET guided dose Reduction for InvOlved site Radiotherapy In early sTage unfavourable Hodgkin lymphoma: a randomized, phase III, non-inferiority study)

Introduction: Treatment of early-stage Hodgkin lymphoma (HL) is extremely successful, with more than 90% cure rate. The mainstay of treatment for early stage Hodgkin's disease includes an approach combining chemotherapy and radiotherapy. The introduction of 18 F-FDG PET for metabolic response assessment has certainly provided the opportunity for a more individualized approach, both in terms of treatment intensification and de-escalation. Therefore, since H10 trial showed that consolidation radiotherapy cannot be safely omitted even in PET-2 negative patients, it becomes now important to re-consider radiation dose de-escalation from the standard 30 Gy to the 20 Gy level in patients achieving a metabolic complete response (mCR) at early PET.

Methods: NCT07256158 PRIORITY is a phase III Italian multicentric, randomized, non-inferiority, interventional study. Patients aged  18 years with unfavourable early stage HL according to GHSG criteria will be treated with 2 cycles of ABVD. Patients in mCR according to 2014 Lugano criteria (DS score 1-3) after 2 cycles ABVD will receive two other ABVD cycles (total 4 cycles) and randomized to standard arm of ISRT 30 Gy vs experimental arm with ISRT 20 Gy. Patients in partial response/progressive disease (DS 4-5) will be withdrawn from trial and will receive further treatment at the discretion of the investigators. The primary endpoint is 3-year Progression-Free Survival (PFS) of the randomized population. Secondary endpoints are: Overall Survival (OS) for the randomized population and for the whole population, PFS for the whole population, incidence of adverse events, RT dose received by organs at risk. Exploratory endpoints are planned: performance of risk-adapted automatic RT re-planning in comparison with manual plans used for clinical treatment, prognostic value of baseline metabolic tumour volume (MTV) and/or tumour lesion glycolysis impact on PFS/OS, association between baseline radiomics and clinical characteristics and/or global clinical outcome. Assuming a 3-year PFS in the standard arm (30 Gy) of 92%, with a non-inferiority margin of 7% for the experimental arm (20 Gy), with 80% power (one-sided alpha 5%), and considering eligibility criteria (Deauville score 1-3 after two ABVD cycles), 518 patients must be enrolled to reach the target. Trial has been recently approved by EC and recruitment is ready to start (June 2026) in 38 Italian centers affiliated to FIL (Fondazione Italiana Linfomi)