ESTRO 2025 - Abstract Book

S2079

Clinical - Urology

ESTRO 2025

3938

Digital Poster Correlations between radiation-induced lymphopenia and risk of failure after post-prostatectomy salvage RT in men receiving elective nodal irradiation Cesare Cozzarini 1 , Adraina Faiella 2 , Andrea Brignoli 3 , Luciana Rago 4 , Elisa Villa 5 , Chiara Deantoni 1 , Andrei Fodor 1 , Roberta Carlevato 6 , Fiorella D'Auria 4 , Giuseppe Ricciardi 7 , Monica Vincenzi 7 , Rosario Mazzola 5 , Oreste Durante 6 , Giuseppe Sanguineti 8 , Fernando Munoz 3 , Claudio Fiorino 7 , Nadia Gisella Di Muzio 1,9 1 Radiotherapy, San Raffaele Scientific Institute, Milan, Italy. 2 Radiotherapy, Istituto Nazionale dei Tumori "Regina Elena, Rome, Italy. 3 Radiotherapy, Ospedale Regionale Parini- AUSL Valle d’Aosta, Aosta, Italy. 4 Radiotherapy, Ospedale San Carlo, Potenza, Italy. 5 Radiotherapy, Cliniche Gavazzeni-Humanitas, Bergamo, Italy. 6 Radiotherapy, A.O. SS. Antonio e Biagio, Alessandria, Italy. 7 Medical Physiscs, San Raffaele Scientific Institute, Milan, Italy. 8 Radiotherapy, Istituto Nazionale dei Tumori "Regina Elena",, Rome, Italy. 9 Università Vita Salute, San Raffaele Scientific Institute, Milan, Italy Purpose/Objective: Elective nodal irradiation (ENI) has an established role in salvage radiotherapy (SRT) for BCR after radical prostatectomy for prostate cancer (PCa). Nevertheless, the radiation-induced lymphopenia (RIL) resulting from larger irradiation fields may mitigate the therapeutic effect of ENI, if not proving detrimental for pts for whom it could be not necessary. Aim of this analysis was to analyze the correlation between RIL and clinical outcome after SRT, with a particular emphasis on the role of ENI volumes and cranio-caudal (CC) extension of lymph-nodal PTV volume (PTVLNv). Material/Methods: This analysis pertains to 171 pts prospectively followed in five Institutes for whom detailed data relative to post-SRT clinical outcome and blood samples at baseline, SRT mid-point and end, and 3,6, 12, 18, 24, 30 and 36 months were available. The median FU was 94 months (IQR 67-116), PSA at SRT 0.31 ng/mL (IQR 0.21-0.49), EQD2 SRT dose to prostatic bed (PB) and lymph-nodal PTV (PTVLN) 74 (IQR 73.14-74.40) and 49.99 (IQR 49.88-51.84) Gy, respectively. ADT was prescribed for 50 pts for a median of 24 months. A total of 1330 blood samples (median 8/patient, IQR 6-9) were available from baseline to 36 months. Median PTVLNv was 1040 cc (IQR 945-1198) and its CC extension arbitrarily calculated from the inferior border of L5 was 45 mm (IQR 38-55). Results: The actuarial 10-year post-SRT biochemical-recurrence free survival (BRFs) was 75%. The low number of clinical failures ruled out any meaningful analysis relative to DFS. Patients were grouped as low-risk (LR, pT2/3a and ISUP≤3, n=69) and high -risk (pT3b and/or ISUP 4-5, n=92), actuarial 10-year BRFS of 90 vs 61%, respectively (p=0.003, HR 4.80). An ANOVA analysis (Fig .1) clearly indicated that the mean ALC counts at 12, 24 and 36 months were significantly lower (p=0.009) in pts experiencing a post-SRT BCR.