RATES OF POST-TREATMENT OEDEMA AND THEIR EFFECTS IN PATIENTS WITH MENINGIOMAS TREATED WITH STEREOTACTIC RADIOSURGERY

Abstract AIMS Stereotactic radiosurgery (SRS) is increasingly used for treating meningiomas, offering an alternative to surgery or fractionated radiotherapy. Oedema following SRS occurs in 20-50% of cases, with 5-43% of patients reporting related symptoms. Typically developing 3-9 months post-treatment, oedema peaks around 6 months and can last up to 18 months. Factors such as tumour location, size, prior surgery, and radiation dose may influence its development. However reported risk factors vary across studies, warranting further investigation. There is considerable variation in recommendations for dose and fractionation for meningioma SRS. This audit aims to evaluate post-treatment oedema rates in meningioma patients treated with SRS at the Royal Marsden Hospital and explores characteristics influencing oedema development and impact on neurological function. METHODS This single-centre retrospective study includes 161 treatments in 135 patients at RMH, since the initiation of our service in 2016. Patient demographic and treatment data were collected prospectively at the time of treatment, obtaining approval from the Institutional Review Board as a service evaluation. Dosimetric data and outcome radiological data were collected retrospectively through EPIC, PACS, radiotherapy planning systems, and the NHS Spine system. Variables examined include tumour characteristics pre-treatment, SRS details (dose, frac- tionation), and outcomes such as presence/absence of oedema, tumour response/recurrence, and neurological symptoms at 3-months and yearly post-SRS. RESULTS Data analysis is due April 2025, collating data from meningioma patients treated with single-fraction (n=25) and fractionated (n=136) SRS. This analysis aims to assess rates of both symptomatic and asymptomatic oedema and investigate potential risk factors. CONCLUSION This study seeks to identify risk factors for oedema in meningioma patients post-SRS and understand its neu- rological sequelae and relationship with radiological outcomes. Findings will help refine treatment strategies, enhancing patient selection and may advise dose and fractionation for SRS.