RADIONECROSIS VERSUS PROGRESSION IN BRAIN TUMORS: RESULTS OF A PROMISING MRI TOOLS

Abstract Background Distinguish between radiation necrosis (RN) and tumor progression, in patients with irradiated primary or metastatic brain tumors, is a diagnostic challenge. Also the use of new MRI sequences, like diffusion, perfusion-weighted and spectroscopy, or PET with new amino acid tracers, is not always able to differentiate these two entities.To overcome this crucial problem, encouraging results have been obtained using the analysis of delayed contrast extravasation MRI to calculate high resolution maps, called “treatment response assessment maps” (TRAMs). Aim of this exploratory analysis is to assess TRAM ability in differentiate between radiation effect and tumor progression in a small cohort of brain tumor patients treated with radiation therapy (RT). Material and Methods Thirty-four patients irradiated for primary and metastatic brain tumors were evaluated. 12 patients have primary brain tumors, 22 patients have brain metastases from different solid tumors. Distinguish by histological subtypes and type of treatment, the 12 patients with primary brain tumors were: 8 glioblastoma, 2 anaplastic astrocitoma, 1 pleomorphic xanthoastrocytoma WHO grade II, and 1 anaplastic xanthoastrocytoma WHO grade III, treated with surgery followed by RT and concomitant and\or adjuvant chemotherapy with temozolomide. Among brain metastatic patients, primary tumor was: 18 non-small cell lung cancer, 2 malignant melanoma, 1 breast cancer and 1 renal cell carcinoma. All of them were treated with stereotactic radiosurgery at the dose of 20-24Gy in 1fraction, or with hypofractionated stereotactic radiotherapy at the dose of 27-30Gy in 3fractions. All images were uploaded and elaborate into the image workstation ([Brainlab AG, Olof-Palme-Straße 9, 81829 Munich]). TRAMs were calculated by subtracting T1 MRI images acquired 5 minutes after contrast injection from the T1 MRI images acquired 60-105 minutes later. On TRAMs, radiation effects appeared as red areas whereas persistent tumoral lesion appeared as blue areas. Results From February 2021, 34 patients have been evaluated, in a prospective study, with this novel MRI modality. During their follow-up, 13patients (38%) showed a clinicoradiologic suspicion of a persistent tumoral lesion or progressive disease, and 21 (62%) a suspicion of RN. For 14patients a brain MET-PET has been performed. TRAMs analysis have shown a fair agreement with clinicoradiologic diagnosis, perfusion-weighted MRI, and PET imaging. Moreover, 7 patients underwent surgical resection, with histopathological confirm of persistent disease in 4 and radionecrosis in 3. Conclusion These preliminary results show the ability of TRAMs evaluation in distinguish between RN and progressive disease. The recruitment of new patients continues, and further evaluations are ongoing to evaluate sensitivity and positive predictive value of TRAMs analysis.