ESTRO 2025 - Abstract Book

S813

Clinical - Gynaecology

ESTRO 2025

1526

Poster Discussion Real-world outcomes of particle beam re-irradiation in gynaecological malignancies Amelia Barcellini 1,2 , Alessandro Vai 3 , Giulia Fontana 4 , Chiara Cassani 5,6 , Jessica Franzetti 2 , Angiolo Gadducci 7 , Concetta Laliscia 8 , Fabio Landoni 9 , Roberta Lazzari 10 , Laura Deborah Locati 1,11 , Domenica Lorusso 12 , Giorgia Mangili 13 , Sandro Pignata 14 , Viviana Vitolo 2 , Ester Orlandi 5,2 1 Department of Internal Medicine and Therapeutics, University of Pavia, Pavia, Italy. 2 Radiation Oncology Unit, Clinical Department, CNAO National Center for Oncological Hadrontherapy, Pavia, Italy. 3 Medical Physics Unit, Clinical Department, CNAO National Center for Oncological Hadrontherapy, Pavia, Italy. 4 Clinical Department, CNAO National Center for Oncological Hadrontherapy, Pavia, Italy. 5 Department of Clinical, Surgical, Diagnostic and Pediatric Sciences, University of Pavia, Pavia, Italy. 6 Unit of Obstetrics and Gynecology, Foundation IRCCS Polyclinic San Matteo, Pavia, Italy. 7 Division of Gynecology and Obstetrics, Department of Clinical and Experimental Medicine, University of Pisa, Pisa, Italy. 8 Department of Translational Medicine, Division of Radiation Oncology, University of Pisa, Pisa, Italy. 9 Unit of Obstetrics and Gynecology, University of Milano Bicocca- IRCCS Fondazione San Gerardo dei Tintori, Monza, Italy. 10 Department of Radiotherapy, IEO European Institute of Oncology IRCCS, Milano, Italy. 11 Medical Oncology Unit, Istituti Clinici Scientific Maugeri IRCCS, Pavia, Italy. 12 Department of Obstetrics and Gynecology, Humanitas University, Milano, Italy. 13 Unit of Gynaecology and Obstetrics, IRCCS San Raffaele Scientific Institute, Milano, Italy. 14 Department of Urology and Gynecology, Istituto Nazionale Tumori, IRCCS-Fondazione G., Napoli, Italy Purpose/Objective: This study aimed to provide real-world evidence on the efficacy and safety of proton beam radiotherapy (PBT) and carbon ion radiotherapy (CIRT) delivered as salvage treatment for recurrent gynaecological cancer recurrence within the previously irradiated field. Material/Methods: Retrospective data were analysed for patients treated between 2017 and 2023. Key outcomes included objective response rate (ORR)—the combined rate of complete and partial responses—and 1- and 2-year local control (LC) survival rates. The secondary endpoint was toxicity. Actuarial outcomes, assessed via radiological follow-up, were evaluated using the Kaplan-Meier method while potential predictors were explored using the Log-rank test. The treatment toxicity was graded using the CTCAE 5.0 scale. Results: 27 patients (median age 64.5 years, range 39-60) for a total of 28 recurrent lesions received PBT (N=12 lesions) or CIRT (N=16 lesions), without any concurrent systemic therapies, with a median total dose of 43.5 Gy[RBE] (range: 39 60 Gy[RBE]) and 48 Gy[RBE] (range: 39-68 Gy[RBE]) respectively. The majority of cases involved cervical (29.6%), endometrial (25.9%), and ovarian (22%) cancers, along with rare and radioresistant tumours like melanomas and sarcomas. Compared to those treated with PBT, the lesions treated with CIRT were characterized by larger volumes (median= 118 [IQR=66, 233.5] vs 99 [IQR=54, 152.3]) and lower alpha/beta ratios (median= 3.8 [IQR=3.5, 4.5] vs 7.3 [IQR=3.5, 10.0]). Despite these unfavourable characteristics in the group treated with CIRT, the ORR did not differ between the two cohorts (75% for PBT and 63% for CIRT, p=0.687), reaching an overall ORR of 68% within 6 months. After a median follow-up of 14.3 months, LC at 1 and 2 years were 100% and 100% for PBT and 83% and 62% for CIRT, respectively ( p=0.075). Among all the factors explored, larger volumes (p=0.035), the failure to achieve ORR (p=0.009) and a lower alpha/beta ratio (p=0.078) negatively impacted the LC. Treatments were well tolerated and no grade ≥ 3 toxicities were observed. Conclusion: Particle beam re-RT in a real-world setting of gynaecological recurrence is effective and safe. The differences in LC and ORR between CIRT and PBT seem to be related to tumour histologies and the larger volumes treated with CIRT. Larger collaborative cohorts and longer follow-up are needed to further validate these findings.