S1117
Clinical – Upper GI
ESTRO 2026
induction chemotherapy, were recruited from three consecutive institutional prospective trials. Absolute lymphocyte counts were obtained before, during, and after CRT. Spleen dosimetric parameters were analyzed, including mean dose, maximum dose, and several volume-dose metrics (V5, V10, V15, V20, V25, V30, and V35), expressed in both absolute volume (cc) and relative percentage of the spleen. Receiver- operating characteristic (ROC) curves and univariate and multivariate logistic regression analyses were performed to identify significant dose thresholds associated with the occurrence and severity of lymphopenia. Survival outcomes were also evaluated. Results: Seventy-eight patients (39 males and 39 females; median age 61.7 years, range 43–76) were analyzed. All patients developed lymphopenia during CRT: 15.4% (n=12) had mild and 84.6% (n=66) had severe grade 3– 4 lymphopenia. Both univariate and multivariate analyses revealed significant correlations between severe lymphopenia and specific splenic dose parameters. The identified thresholds were 5 Gy for mean dose, 27 Gy for maximum dose, 35% for V5, 20% for V10, 11% for V15, and 9% for V20. Severe lymphopenia was also significantly associated with absolute spleen volume doses: 147 cc for V5, 65 cc for V10, 27 cc for V15, and 21 cc for V20. The mean baseline volume of the spleen was 347±178 cc. Follow- up imaging was available for 76 patients one month after the end of radiotherapy, 26 patients 12 months after, and 13 patients 24 months after. The mean spleen volume at the first, second and third follow-up appointments was 348 ± 168 cc, 303 ± 123 cc and 270 ± 92 cc, respectively. Conclusion: This study demonstrates a strong association between splenic radiation exposure and the development of severe treatment-related lymphopenia in patients undergoing CRT for pancreatic cancer. These findings support the need to consider the spleen as an organ of interest during pancreatic irradiation and to establish dose guidance aimed at preserving immune function. Incorporating spleen-sparing strategies into treatment planning may improve immune preservation, treatment tolerance, and ultimately clinical outcomes. Keywords: Pancreatic cancer, Spleen, Dose guidance
Conclusion: EDIC showed no significant association with overall survival or lymphocyte nadir levels, suggesting that it is not an independent prognostic factor in thoracic esophageal cancer. References: 1.Xu et al. (2020) Radiotherapy and Oncology 146:180– 86. 2.Qiu et al. (2023) Frontiers in Immunology 14:1066255.3. De Kermenguy et al. (2025) International Journal of Radiation Oncology Biology Physics.4. Zhao et al. (2025) BMC Cancer 25(1):238. 5.Zhang et al. (2024) BMC Cancer 24(1):779.6.Luan et al 2025. Radiotherapy and Oncology 212:111123. 7.McCall et al 2022. Radiotherapy and Oncology 174:133–40. Keywords: EDIC, Esophagus, Lymphocyte Impact of Splenic Radiation Dose on Treatment- Related Lymphopenia in Patients with Pancreatic Cancer (MEUSA Study) Gian Marco Petrianni 1 , Michele Fiore 2,1 , Gabriele D'Ercole 1 , Elena Onorati 1 , Pasquale Trecca 1 , Rita Alaimo 1 , Daniele Carlotti 1 , Valerio Marè 1 , Guenda Meffe 1 , Edy Ippolito 2,1 , Sara Ramella 2,1 1 Operative ResearchUnit of Radiation Oncology, Fondazione Policlinico Universitario Campus Bio- Medico, Rome, Italy. 2 Research Unit of Radiation Oncology,Department of Medicine and Surgery, Università Campus Bio-Medico di Roma, Rome, Italy Digital Poster 4499 Purpose/Objective: Pancreatic cancer is one of the most aggressive malignancies, with poor prognosis and limited therapeutic options. Radiation-induced lymphopenia (RIL) is a frequent adverse effect that can compromise immune response and survival outcomes. This study aimed to quantify the incidental radiation dose delivered to the spleen during chemoradiotherapy (CRT) for pancreatic cancer and to evaluate its correlation with treatment-related lymphopenia. Material/Methods: Patients with borderline resectable or unresectable pancreatic cancer treated with CRT, with or without
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