S499
Clinical - Haemotology
ESTRO 2026
(27–36 Gy). Seven (58%) started with 4 Gy in 2 fractions; 5 achieved complete response (CR) with 4 Gy alone, while 2 with partial response (PR) were escalated to 24 Gy (10 × 2 Gy) and converted to CR. Final response was CR in all 12 patients (100%). At a median follow-up of 42 months (3–112), no local progression occurred, yielding 100% local control and local progression-free survival (PFS). One MCL patient developed systemic relapse (testicular and pulmonary) 12 months after RT, managed with rituximab, dexamethasone, high-dose cytarabine and oxaliplatin (R-DHAOx) followed by ibrutinib, while maintaining complete orbital remission; overall PFS was 92% (11/12). Acute toxicity was grade 1–2 conjunctivitis, blepharitis, or radiodermatitis; late effects included cataract (n=2) and ptosis (n=1). No ≥ G3 events occurred. Conclusion: Orbital RT achieved 100% local control and local PFS with minimal toxicity across exclusive, adjuvant, consolidative, and relapse scenarios. Most patients benefited from 4 Gy alone, while escalation to 24 Gy was effective in partial responders. Even in MCL with systemic relapse at 12 months, orbital RT ensured durable local control. These results support orbital RT as a safe, effective, and dose-tailorable strategy for both indolent and aggressive subtypes. References: Pinnix CC et al. Response-adapted ultra-low-dose vs standard-dose RT for indolent lymphoma: a randomized trial. JAMA Oncol. 2024;10:1195– 1203.Pinnix CC et al. Ultra-low-dose RT in ocular adnexal lymphoma: outcomes and toxicity. Head Neck. 2017;39:1095–1100.Martinet S et al. Radiotherapy for orbital lymphoma: long-term results. Int J Radiat Oncol Biol Phys. 2003;55:892–898.de Castro B et al. Four Gy and staged escalation in ocular adnexal lymphoma. Rep Pract Oncol Radiother. 2022;27:467–473.Zucca E et al. ESMO Guidelines: marginal zone lymphomas and extranodal disease. Ann Oncol. 2020;31:317–328.Yahalom J et al. ILROG guidelines for RT in extranodal lymphomas. Int J Radiat Oncol Biol Phys. 2015;92:11–31. Keywords: Orbital lymphoma, radiotherapy, ultra-low- dose RT Digital Poster 301 Spleen dose predicts lymphopenia in Radiotherapy alone for upper GI low-grade B-cell lymphoma Yoshikazu Kagami 1 , Kazunori Miyaura 1,2 , Masako Kato 1 , Emi Nishimura 1 , Kosuke Toyofuku 1 , Atsuhito Sekimoto 1 , Atsushi Imai 3 , Yukiko Ozawa 3 , Hidenori Shinjo 4 , Akifumi Niiya 4 , Madoka Morota 5 , Rei Kobayashi 5 , Yoshinori Ito 1
Digital Poster 64
Radiotherapy for orbital lymphomas: outcomes, toxicity and dose adaptation in a single university center. Suyapa M. Melendez Varela, Victoria Concepción Fernandez, Ana M Varela Pazos, Matias D Acosta, Diego F Acuña Viteri, Paula Vilariño Fernandez, Ana M Carballo Castro, Luis M Cascallar Caneda Radiation Oncology, Hospital Clínico Universitario de Santiago de Compostela, Santiago de Compostela, Spain Purpose/Objective: Orbital/ocular adnexal lymphomas are uncommon. Most are indolent extranodal marginal zone B-cell lymphomas (MALT), but aggressive histologies such as diffuse large B-cell lymphoma (DLBCL) and mantle cell lymphoma (MCL) also occur and require distinct management. We assessed outcomes, toxicity, and practice patterns of orbital radiotherapy (RT), including a response-adapted, ultra-low-dose strategy. Material/Methods: We retrospectively reviewed 12 consecutive patients treated between 2015–2025. Variables included demographics, histology (WHO 2016/2022), Ann Arbor stage, orbital subsite, RT indication (exclusive, adjuvant, consolidative, relapse), technique (3D- CRT/VMAT), dose/fractionation, image guidance, organs at risk, response (Lugano/Deauville), toxicity (CTCAE v5.0), and survival. Techniques included 3D- CRT and VMAT. Image guidance was performed with cone-beam CT (CBCT) in 7 patients, while the remaining 5 treated with 3D-CRT in earlier years were verified with portal imaging using an electronic portal imaging device (EPID). Results:
Median age was 66 years; 58% female. Histology: MALT 10/12 (83%), DLBCL 1/12 (8%), MCL (8%). Stage IEA 10/12 (83%), IVA 2/12 (17%). Subsites: conjunctiva 6, lacrimal gland 2, diffuse/intraconal 3, eyelid 1. Indication: exclusive 6 (50%), adjuvant 2 (17%), consolidative 17%, relapse 17%. Technique: 3D-CRT 8 (67%), VMAT 4 (33%); CBCT in 7 (58%) and EPID in 5 (42%). Five patients (42%) received conventional doses
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