ESTRO 2024 - Abstract Book

S914

Clinical - CNS

ESTRO 2024

3. Chun S-W, Kim KM, Kim M-S, Kang H, Dho Y-S, Seo Y, Kim JW, Kim YH, Park C-K. Adjuvant radiotherapy versus observation following gross total resection for atypical meningioma: a systematic review and meta-analysis. Radiat Oncol (2021) 16:34. doi: 10.1186/s13014-021-01759-9

4. Zeng Q, Shi F, Guo Z. Effectiveness of Postoperative Radiotherapy on Atypical Meningioma Patients: A Population Based Study. Front Oncol (2019) 9:34. doi: 10.3389/fonc.2019.00034

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Digital Poster

Post-radiosurgery response for intracranial meningioma: analysis method and cut-off value definition

Valentina Pinzi 1 , Anna Viola 2 , Riccardo Pascuzzo 3 , Marcello Marchetti 1 , Sara Morlino 1 , Laura Fariselli 1

1 Fondazione IRCCS Istituto neurologico Carlo Besta, Radiation Oncology, MILAN, Italy. 2 Isituto Oncologico del mediterraneo, Radiation Oncology, Catania, Italy. 3 Fondazione IRCCS Istituto neurologico Carlo Besta, Radiology, MILAN, Italy

Purpose/Objective:

Defining both a threshold of progression and the optimal endpoint for clinical trials on radiation therapy for benign meningioma is difficult. In fact, the growth rates of meningiomas are variable, and progression-free survival (PFS) requires long-term follow-up. While there is no standardized set of criteria for assessing control, it is clear that the criteria typically used to evaluate other brain tumors, such as high-grade glioma or metastases, may not be well suited for evaluating meningiomas. Volumetric analysis of Magnetic Resonance Imaging (MRI) has emerged as a promising method for detecting changes in slowly progressing brain tumors. [1] In light of this, we conducted an analysis of this approach in the context of post-radiosurgical intracranial meningiomas within the framework of a prospective clinical trial. The primary aim of the present study was to validate a volumetric assessment method after fractionated radiosurgery (f-RS) treatment of benign intracranial meningiomas. Secondary aims were evaluation of a cut-off to define progression, stable or partial response and volumetric response after f-RS. To validate the volumetric assessment, we appraised delta values of volume variations (ΔV) and computed the relative percentages (ΔV%). To evaluate tumor response, a volumetric analysis has been performed by means of co registration of each follow-up MRI on baseline MRI and contouring of the lesion on each post-treatment MRI. First radiological follow-up was scheduled 4 months after the treatment, then every 6 months throughout the first and second years, and subsequently, every 12 months, for 5 years at least. The ΔV% at last follow -up were clustered by the k-means method [2], which partitions the data into k groups starting from random assignments and obtaining the final groups such that the sum of squares from individual values to the assigned cluster centres is minimized. The optimal number of clusters was computed through the “gap” statistic, which compares the total intra -cluster variation for different values of k with their expected values under null reference distribution of the data (i.e., a distribution with no clustering) generated using Monte Carlo simulations [3]. Such clustering method was used to calculate a new cut-off for response-to-treatment definition by repeating the clustering procedure 1000 times and selecting the cut-off value that most often was used by the algorithm to separate the clusters. Material/Methods: