ESTRO 2020 Abstract book

S535 ESTRO 2020

Conclusion The difference in time to engraftment and occurrence of acute and chronic GVHD could be attributed to the difference in dose rate between the treatment cohorts. To increase the understanding of dose rate effects in haematological recovery, a larger cohort should be investigated. PO-0917 Radiotherapy-based approach for the treatment of solitary plasmacytoma A. Alghisi 1 , P. Borghetti 1 , M. Maddalo 1 , A.M. Roccaro 2 , A. Tucci 3 , S.M. Magrini 1 , A. Lo Casto 4 , M.L. Bonù 1 , D. Tomasini 1 , A. Baiguini 1 , G. Peretto 1 , M. Buglione 1 , L. Triggiani 1 1 Spedali Civili di Brescia, Department of Radiation Oncology- Brescia University, Brescia, Italy ; 2 Spedali Civili di Brescia, CREA Laboratory, Brescia, Italy ; 3 Spedali Civili di Brescia, Division of Haematology- Department of Clinical Oncology, Brescia, Italy ; 4 University of Palermo, Radiation Oncology, Palermo, Italy Purpose or Objective Solitary plasmacytoma (SP) is characterized by a single mass of clonal plasma cells, without any evidence of systemic involvement or bone marrow (BM) plasmacytosis. It can present either as solitary bone (SBP) or as extramedullary (EMP) plasmacytoma. Definitive RT can result in long-term local control of the SP. Due to the small number of patients (pts) and narrow range of doses, phase III randomized trials are lacking and the optimal dose of radiation for treating SP is not clearly established. The aim of this study is to further support for the potential use of RT for the treatment of SP. Material and Methods Clinical data of all pts treated for SP at our Institution between 1992 and 2018 were reviewed. Pts with a diagnosis of SBP or EMP based on a biopsy showing features characteristic of SP along with a normal BM biopsy, and without evidence of systemic disease attributing to multiple myeloma (MM) were considered eligible. Results A total of 42 consecutive pts were analyzed. The median follow-up was 84.8 months (range 6.2-265.7 months). Details and characteristics of pts are shown in Table 1. EBRT was used with all pts. The prescribed radiation dose ranged from 20 Gy to 50 Gy, with a median of 46 Gy and a dose per fraction ranging from 1.4 to 4 Gy. The equivalent dose (EQD2) ranged from 23.3 to 50 Gy, with a median of 46 Gy, calculated by using a ratio of α/β=10. Radiation dose did not differ significantly as a function of sex, type of SP, tumor size; conversely differs significantly as a function of age ( p=0.04) . The 5y-OS and 10y-OS were respectively 96% and 91%. Local recurrences developed in 21.4% of pts (9/42). 16 pts progressed to MM (38.1%). The 5y-progression to MM free survival (PMFS) and the 10y- PMFS were respectively 68.6% and 61.9%. Impact of several factors on modulating OS was evaluated. Specifically, age at diagnosis was the only significant prognostic factor of OS (p=0.005), whereas type of treatment, surgery, pain and tumor size were not predictive.

Conclusion Our data confirm the good results achievable with RT to treat SP. Also from our analysis, there is no statistically significant correlation between higher doses and better disease control. Similarly, no correlation between outcomes and type of SP has emerged. No statistically significant correlations were found that could define which pts have the greatest possibility of evolving into MM. Probably other biological factors can influence the outcome of the SP. PO-0918 Early-stage primary bone lymphoma: a single- center experience. A.A.A. Geng Cahuayme 1 , R. Vergés Capdevila 1 , J. Giralt López de Sagredo 1 , V. Reyes López 1 1 Hospital Universitario Vall d'Hebron, Radiation Oncology, Barcelona, Spain Purpose or Objective Primary bone lymphoma (PBL) is a rare entity. PBL accounts for less than 2% of all malignant lymphomas in adults, between 3 to 7% of primary bone malignancies, and less than 1% of all non-Hodgkin lymphoma. Most studies recommend combined modality therapy, however there is no standard treatment for PBL in limited stage. Randomized studies are not available in the literature to obtain optimal management due to the low incidence of the disease. Upon the need for more data on limited stage PBL in order to manage this illness properly, we retrospectively analysed all the PBL cases in our center. Material and Methods Data from 270 patients with pathological proven non- Hodgkin lymphoma (NHL) who received radiotherapy (RT) from January 2008 to August 2019 at Vall d’Hebron University Hospital were retrospectively analyzed. Patients were included in the study if they had any of the following factors: (1) PBL at diagnosis; (2) age ≥ 18 years; (3) histological diagnosis of lymphoma; (4) stage IE-IIE according to the Lugano classification; (5) complete staging work-up with whole body positron emission tomography/computed tomography (PET/CT) scanner and bone marrow biopsy; and (6) no evidence of immunodeficiencies. Exclusion criteria were all other nodal and extranodal - including bone marrow - involvement. Bone involvement was defined by percutaneous or surgical bone biopsy. In total, 6 patients were finally included. Subsequently, we analyzed the clinical features, management and prognosis of these cases. Results