ESTRO 2020 Abstract book

S275 ESTRO 2020

to ISRT and INRT principles. All patients were treated with a high dose gradient RT technique (IMRT-VMAT). Results With a median follow-up time of 54 months (range 12-115), RFS and OS were extremely high, with 5 years rates of 91.5% and 98.4%, respectively, in the overall population (Fig.1a). After stratification for GHSG classification, 5- years RFS was 95%, 90% and 92% respectively in EF, EU and ADV groups. (Fig.1b). Three patients (1.4%) died and 15 (7%) relapsed, with only 3 in-field relapses (1.4%). The only predictive factor of worse RFS at the univariate and multivariate analyses was the persistence of a metabolic uptake at the end of chemotherapy (p <0.001), as RFS at 5 years was 93.4% in patients achieving a complete response and only 67.5% in patients with incomplete remission after CT (Fig.2).

approach to achieve omission of consolidating radiotherapy following combination chemotherapy due to the risk of late effects. Event-free survival rates decrease with up to 10% when radiotherapy is omitted, but salvage treatment is effective and overall survival rates are similar so far. However, intensive salvage treatment is also associated with significant late effects. It is recognized that most relapses occur within the initially involved sites if radiotherapy is not used. Here, we analyze the relapse- localization relative to the initially involved site, and if irradiated, to the irradiated site in pediatric patients with HL. Material and Methods The Danish Childhood Cancer Registry was used to identify children diagnosed with HL and those who relapsed from 1990–2018 at our institution. Patient characteristics, treatment details (including radiotherapy plans), and diagnostic imaging were collected. We merged scans from the time of diagnosis and the time of relapse using the Eclipse treatment planning system (Varian Medical Systems) and visually assessed the relapse-localization relative to the initially involved site and, if irradiated, the irradiated site. Results A total of 90 children were diagnosed with HL at our institution and in the same period 10 relapses occurred (crude relapse-rate 11.1%). Patient characteristics are shown in Table 1. Median time to relapse was 6 months (range 3–54). Out of 10 patients 9 relapsed within the initially involved site. Four patients had received radiotherapy and 3 relapsed within both the initially involved and irradiated site (1 single site, 2 multiple sites). Relapse-localization in relation to the initially involved site is shown in Figure 1. One patient relapsed outside of both the initially involved site and the irradiated site 3 months after end of treatment. Out of 5 patients with initially bulky disease, 2 relapsed within (no radiotherapy) and 3 relapsed outside (2 irradiated, 1 not) the site of bulky disease.

Conclusion In a large cohort of HL patients, followed-up for many years, we observed that modern delivery techniques such as IMRT/VMAT, combined with a reduction of the targets of treatment in respect of the ISRT-INRT definition, is safe and effective with relapse and survival rates at 5 years comparable to those obtained with 3D-conformal radiotherapy. OC-0460 Relapse-localization in pediatric patients with Hodgkin lymphoma A.Y. Lundgaard 1 , L.L. Hjalgrim 2 , A.K. Berthelsen 1 , L. Specht 1 , L. Borgwardt 3 , M.V. Maraldo 1 1 Rigshospitalet, Department of Clinical Oncology, Copenhagen, Denmark ; 2 Rigshospitalet, Department of Pediatric Hematology and Oncology, Copenhagen, Denmark ; 3 Rigshospitalet, Department of Clinical Physiology- Nuclear Medicine and PET, Copenhagen, Denmark Purpose or Objective Radiotherapy is the single most effective modality to achieve local control of Hodgkin lymphoma (HL). However, large treatment fields of the past are associated with late toxicity and increased morbidity and mortality in long- term survivors. In the management of pediatric patients with HL, recent treatment protocols use a response-based