S1218
Clinical - Urology
ESTRO 2026
through logistic regression. The impact of many clinical and dosimetry covariates was also tested, including baseline IBDQ values. For the questions showing significant association between Δ IBDQ ≤ -2 and acute and/or late lymphopenia, multi-variable models were assessed by bootstrap-based selection of the best combination of the three major predictors, including alternatively acute G3+ or late G2+ lymphopenia in model’s building. Results: 211/47 patients experienced acute G3+/late G2+ lymphopenia. IBDQ-b and two symptoms (frequency IBDQ1, urgency IBDQ24) showed significantly different time patterns if stratified according to lymphopenia, as shown in the Figures. Univariate analysis showed that acute and/or late lymphopenia was significantly associated to Δ IBDQ ≤ -2 for IBDQ1, IBDQ24 and IBDQ26 (accidental soiling). Patients with IBDQ1/IBDQ24/IBDQ26 ≤ -2 were 46/17/24. In the multi-variable models, acute lymphopenia was the strongest predictor for all three end-points with OR=2.4-2.6 (95%CI=1.2-1.4 and 4.6-5.2, p-value:0.001- 0.02). Models showed good calibration and moderate discrimination (AUC:0.62-0.68). Late lymphopenia was strongly associated with IBDQ24 ≤ -2 (OR=3.9; 95%CI:1.5-10.0) in the best multi-variable model (AUC=0.66). Among other retained variables, the most relevant were baseline IBDQ (for IBDQ1) and adjuvant hormonal therapy for IBDQ24.
Mini-Oral 2184
Lymphopenia after whole-pelvis Radiotherapy in prostate Cancer patients is a major predictor of late patient-reported Intestinal Toxicity Giuseppe Ricciardi 1 , Giusepppe Sanguineti 2 , Monica M Vincenzi 1 , Barbara Avuzzi 3 , Domenico Cante 4 , Nadia G Di Muzio 5 , Giuseppe Girelli 6 , Alessandro Magli 7 , Fernando Munoz 8 , Barbara Noris Chiorda 3 , Maddalena Pavarini 1 , Luciana Rago 9 , Vittorio Vavassori 10 , Elisa Villa 10 , Justyna M Waskiewicz 11 , Roberta Carlevato 12 , Tiziana Rancati 13 , Claudio Fiorino 1 , Cesare Cozzarini 5 1 Medical Physics, IRCCS San Raffaele Hospital, Milano, Italy. 2 Radiotherapy, IRCCS Regina Elena National Cancer Institute, Roma, Italy. 3 Radiotherapy, IRCCS Istituto Nazionale dei Tumori, Milano, Italy. 4 Radiotherapy, ASL TO4 Ospedale di Ivrea, Ivrea, Italy. 5 Radiotherapy, IRCCS San Raffaele Hospital, Milano, Italy. 6 Radiotherapy, Ospedale ddegli Infermi, Biella, Italy. 7 Radiotherapy, Azienda ospedaliera universitaria S Maria della Misericordia, Udine, Italy. 8 Radiotherapy, IOspedale Regionale Parini-AUSL Valle d'Aosta, Aosta, Italy. 9 Radiotherapy, IRCCS Crob, Rionero in Vulture, Italy. 10 Radiotherapy, Cliniche gavazzeni-Humanitas, Bergamo, Italy. 11 Radiotherapy, Comprensorio Sanitario DI Bolzano, Bolzano, Italy. 12 Radiotherapy, Azienda Ospedaliera SS Antonio e Biagio e Cesare Arrigo, Alessandria, Italy. 13 Data Science Unit, IRCCS Istituto Nazionale dei Tumori, Milano, Italy Purpose/Objective: Clinical implications of lymphopenia after Whole-Pelvis Radiotherapy (WPRT) for prostate cancer are poorly explored. Current investigation aimed to quantify the impact of prospectively and longitudinally registered lymphopenia on late (2-year) patient-reported intestinal toxicity, assessed using the Inflammatory- Bowel-Disease-Questionnaire (IBDQ). Material/Methods: Between 2012 and 2021, 884 patients treated in 14 Institutes with conventional/moderate hypo- fractionation were enrolled (IHU study; ClinicalTrials.govNCT2803086 [1-3]), including the prospective collection of patient-reported toxicities and blood samples data (at baseline/mid-RT/end- RT/6months/every 6 months up to 5years). Patients with complete data (IBDQ/ALC counts) at baseline, mid or end-RT and 2-year and with baseline IBDQ ≥ 5 were considered (n=555). Patients with CTCAE v4.03 acute Grade ≥ 3 (G3+,ALC<500/ μ L) and 2-year Grade ≥ 2 (G2+,ALC<800/ μ L) were identified. The impact of both lymphopenia end-points on the longitudinal changes of the IBDQ bowel domain (IBDQ-b) and of each single question was investigated by Mann-Whitney test. Then, the association between late moderate/severe changes ( ≤ -2 against the baseline on a 1-7 scale, Δ IBDQ ≤ -2) and IBDQ-b/each question was investigated
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