P14.21.B ROLE OF 11C-METHIONINE POSITRON EMISSION TOMOGRAPHY EMPLOY BEYOND THAT ADVANCED MAGNETIC RESONANCE IMAGING FOR TARGET VOLUME DELINEATION IN PATIENTS UNDERWENT RE-IRRADIATION FOR RECURRENT GLIOBLASTOMA
Authors: Navarria P , Pessina F , Bellu L , Clerici E , Vernier V , Politi L , Raspagliesi L , Di Cristina L , Simonelli M , Di Pasquale A , Bono B , Franzini A , Evangelista L , Scorsetti M 
Published: October 2024

Abstract

BACKGROUND
Reirradiation for recurrent glioblastoma patients is a challenging and important topic under investigation. No clear evidences exists regarding indications, sequences with other therapeutic approach, optimal dose to delivered, and fractionation to use. But even more, the critical point is reaching correct tumor delineation based on imaging. The contrast enhancement T1-weighted-MRI usually outlines the most aggressive tumor area, and T2-weighted FLAIR-MRI allows a more accurate definition of the infiltrating microscopic disease growing outside the enhanced area on T1 MRI. More recently, different reports suggest that the use of carbon-11-methionine positron emission tomography ([11C]-methionine PET ([11C]METPET) improves diagnostic accuracy for treatment planning allowing more precise viable tumor cell identification. Evidence regarding the predictive, and prognostic value is still lacking, and its use in planning radiation therapy, is debated. For this reason, we investigated the role of [11C]-Methionine PET (PET-MET) in a cohort of adults patients with recurrent GBM treated with adiation therapy aiming to evaluate how it could modify target volume delineation, and if it could detect eventually tumor cells not otherwise visible.

MATERIAL AND METHODS
Patients with recurrent GBM, and an interval time (IT) from previous RT &gt; 6 months were included. Simulation CT scan, MRI with different sequences and a 11CMETPET were performed in all patients, and images were co-registrated one with each other to define the target volume. Two different target volume were defined: Biological Target Volume (BTV) corresponded to the pathological uptake on METPET, and Clinical Target Volume (CTV) defined as the abnormalities volume on postcontrast T1 MRI. Correlation between BTV and CTV were recorded.

RESULTS
From September 2013 to January 2024, 121 patients received reirradiation for recurrent GBM. The median age was 52 years, and majority had KPS 90-100. In all cases, the whole BTV was inside the CTV, and in 10 (11%) patients, part of the BTV was outside the CTV into the FLAIR abnormalities area. The overlap between BTV and CTV showed low correlation between the two volumes, with CTV not always fully included in BTV. According to the 11CMETPET uptake, CTV was modified.

CONCLUSION
11CPET-MET allowed to detect areas at higher risk of recurrent. A challenging issue is represented by integration of morphological, and functional imaging to define CTV in the setting of reirradiation. This results are promising and could permit to better define the tumor volume, to reduce the dose at organs at risk, and potentially to allow a dose escalation for a better local control improving patients outcome in recurrent glioblastoma patients.