ESTRO 2023 - Abstract Book

S542

Sunday 14 May 2023

ESTRO 2023

Results Figure 2 shows nine structures exhibiting significant DTI signal changes after RT. Posterior thalamic radiation showed the greatest alterations of the DTI parameters and a significant dose- and time-dependency of MD (-0.111%/month, - 0.135%/Gy), RD (-0.14%/month, -0.171%/Gy), and AD (-0.09%/month, -0.1%/Gy). The strongest correlation of FA with time appeared in superior longitudinal fasciculus (0.045%/month) and with dose in internal capsula (0.056%/Gy). All significant changes represented decreasing MD, RD, and AD and increasing FA after irradiation. No significant correlations were detected in medial lemniscus.

Conclusion Several WM structures showed significant time- and dose-dependent DTI signal changes after RT, which might indicate a stronger radiosensitivity of these structures. The results are in agreement with the investigation of dose-dependent irradiation effects on WM diffusion by Raschke et al. ( Radiother Oncol. 2019; 140 :110–115) and Dünger et al. ( Radiother Oncol. 2021; 164 :66–72). PD-0652 Re-irradiation of recurrent intracranial meningiomas: an Italian multicenter retrospective study I. Desideri 1 , I. Morelli 1 , L. Visani 2 , D. Greto 1 , B. Detti 3 , Z. Perini 4 , E. Zivelonghi 5 , G. Bulgarelli 5 , V. Pinzi 6 , P. Navarria 7 , E. Clerici 7 , A.M. Ascolese 8 , P. Anselmo 9 , D. Amelio 10 , M.F. Osti 9 , G. Minniti 11 , L. Livi 3 , D. Scartoni 10 1 Azienda Ospedaliero Universitaria Careggi, Università di Firenze, Radiation Oncology, Florence, Italy; 2 Istituto Fiorentino di Cura e Assistenza (IFCA), Cyberknife Center, Florence, Italy; 3 Azienda Ospedaliero Universitaria Careggi, Università di Firenze, Radiation Oncology , Florence, Italy; 4 Ospedale s. Bortolo, CyberKnife Unit, Vicenza, Italy; 5 Hospital Trust of Verona, Physics Department, Department of Neurosciences, Verona, Italy; 6 Fondazione IRCCS Istituto neurologico C. Besta, Radiotherapy Department, Milan, Italy; 7 IRCCS Humanitas Research Hospital, Radiotherapy and Radiosurgery Department, Milan, Italy; 8 St. Andrea Hospital, Sapienza University of Rome, Radiotherapy Department, Rome, Italy; 9 Santa Maria Hospital, Radiotherapy Oncology Centre, Terni, Italy; 10 Azienda Provinciale per i Servizi Sanitari , Proton Therapy Center, Trento, Italy; 11 University of Siena, Department of Medicine, Surgery and Neurosciences, Siena, Italy Purpose or Objective Re-irradiation (reRT) of intracranial meningiomas is often difficult due to the limited radiation tolerance of the surrounding tissue and the risk of side effects. Aim of this analysis is to report outcomes, toxicities and prognostic factors of reRT in a large cohort of patients with recurrent meningiomas (RM) treated with different RT modalities. Materials and Methods We collected a multi-institutional database of meningioma patients who recurred after prior radiation therapy and underwent reRT with different modalities: radiosurgery (SRS), multi-fraction stereotactic radiotherapy (f-SRT), proton therapy (PT), Intensity-Modulated radiotherapy (IMRT) and External Beam radiotherapy (EBRT). Biologically Equivalent Doses in 2 Gy-fractions (EQD2) for normal tissue and tumor were estimated for each RT course (a/b =2 for brain tissue and a/b = 4 for meningioma), as well as Biological Effective Dose (BED). The primary outcome measure was progression-free survival (PFS). Secondary outcomes included overall survival (OS) and treatment-related toxicity. Toxicity was assessed according to Common Terminology Criteria for Adverse Events version 5.0 (CTCAE v5.0). Kaplan–Meier curves were