ESTRO 2025 - Abstract Book

S897

Clinical - Haematology

ESTRO 2025

Key patient characteristics are summarized in Table 1. Seven patients had B-cell lymphoma (three diffuse large B cell lymphoma (DLBCL), two MALT lymphoma, one follicular, and one mantle-cell) while one had T-cell/NK lymphoma. Radiotherapy was intended as radical treatment for four patients (including the T-cell/NK case, which was followed by chemotherapy), as salvage therapy for three, and as CAR-T bridging for one. Two patients had orbital involvement, while six presented with cervical lymph node involvement (two with concurrent nasopharyngeal disease and one with oropharyngeal disease). Median GTV was 5.74 cc (range: 1.14– 194.07 cc), median CTV was 127.01 cc (range: 25.63–496.64 cc), and median PTV was 210.37 cc (range: 51.19–709.45 cc). Prescribed dose was 24-50 Gy in 2 Gy fractions for 7 patients and 24 Gy in 3 Gy fractions for one patient. All patients experienced acute toxicity. The maximum toxicity grade was G1 for five patients and G2 for three by the end of RT. The most common side effects were mucositis (75%, with 50% G2), dermatitis (50%, all G1), esophagitis (50%, 37.5% G2), xerophthalmia (37.5%, all G1, seen in all orbital cases), dysgeusia (37.5%, 25% G2), epiphora (25%, all G1), and pharyngodynia (25%, all G1). One month post-radiotherapy, seven patients continued to experience G1 toxicity, but no toxicities ≥ G2 were noted. Initial radiological assessment, performed after a median of 101.5 days, revealed complete response in all cases. Over a median follow-up of 433 days, no local disease progression was observed, though one patient developed distant progression. Conclusion: radiotherapy for NHL with H&N localization using a 1.5 T MRI-linac was feasible, with no > G2 toxicity and optimal response rate and disease control. Digital Poster Retrospective analysis of toxicities after total body irradiation without lung shielding Justin Nguyen 1 , Daphne Van Kampen 1 , Christophe Vandekerkhove 2 , Marianne Paesmans 3 , Chloé Spilleboudt 4 , Paul Van Houtte 1 , Sebastien Penninckx 2,1 , Dirk Van Gestel 1 1 Radiotherapy, Institut Jules Bordet, Brussels, Belgium. 2 Medical physics department, Institut Jules Bordet, Brussels, Belgium. 3 Data Centre, Institut Jules Bordet, Brussels, Belgium. 4 Hematology Department, Institut Jules Bordet, Brussels, Belgium Purpose/Objective: Idiopathic Pneumonia Syndrome (IPS) is a diffuse alveolar injury of unknown etiology defined by objective and standardized criteria. It represents a significant acute pulmonary toxicity following total body irradiation (TBI) with high mortality rates. To date, no studies have assessed the toxicity associated with the absence of lung shielding using the most recent definitions of IPS. Material/Methods: This study included 108 patients (median age of 33 years) who underwent hematopoietic stem cell transplantation between 1995 and 2021. The primary objective was to assess the incidence of IPS. Descriptive comparisons were made with data from the existing literature. A systematic literature review was conducted to identify studies comparable to our analysis. Results: The incidence of IPS was 6%, with 4% occurring within the first 100 days post-transplant. Acute hypoxemia (occurring before day 100) was observed in 18 patients (17%), with a fatal outcome in 12 cases. Among these, there were 2 cases of idiopathic interstitial pneumonitis (0% mortality), 4 cases of IPS (100% mortality), 7 cases of Keywords: lymphoma,MR-linac,adaptive 2168