P17.22.B EFFICACY AND TUMOR DYNAMICS OF DAILY MRI-GUIDED ONLINE ADAPTIVE RADIOTHERAPY FOR BRAIN GLIOMA

Abstract BACKGROUND Magnetic resonance image (MRI) guided radiotherapy has the potential to improve outcomes in patients with brain glioma. This study aims to evaluate the tumor dynamics, efficacy and potential benefits of MRI-guided online adaptive radiotherapy (MRIgOART) for brain glioma. MATERIAL AND METHODS Patients with diagnosed brain glioma who received chemoradiotherapy (chemoRT) of 54 ~ 60 Gy in 30 fractions on the 1.5T MR-Linac were eligible for this study. The MRIgOART including adapt-to-shape (ATS) and adapt-to-position (ATP) approaches employed daily MR scan to correct the treatment errors and assess treatment response. The pre-treatment and inter-fractional tumor changes were quantified by absolute/relative volume (Vrel), Hausdorff distance (HD) and Dice similarity coefficient (DSC) metrics. Covariables evaluated included: extent of surgery, O6-methylguanine-DNA-methyltransferase methylation (MGMT), 1p/19q status, telomerase reverse transcriptase (TERT) mutation status, and isocitrate dehydrogenase mutation (IDH) status. Target coverage and normal brain tissue constraints were used to compare ART and non-ART plans. The pattern of failure, progression-free survival (PFS) and overall survival (OS) were assessed in the study. RESULTS Fifty-seven patients treated between 2021 and 2023 were included in this study. Pronounced pre-treatment tumor changes were observed, with statistical significance noted in patients who experienced a longer interval (>10 days) between simulation and Fx1 (P < 0.001). Overall, the tumor volume gradually decreased during treatment, while changes in its position and shape became increasingly significantly. We found that there were correlations between extent of surgical resection and DSC, as well as between prognosis and HD. The ATS adaptive radiotherapy was implemented in 52.6% of patients (30/57) during treatment at least once fraction. The first ATS fraction always occurred in Fx1 ~ 10 for 60% (18/30) patients. The frequency of ATS was significantly higher in TERT wild-type compared to TERT mutant (P = 0.013). The results showed the median PFS was 13 months (95% CI, 10.2 ~ 15.8 months) and OS was 28 months (95% CI, 23.3 ~ 32.7 months) for high-grade glioma (HGG) patients. And we found 58.9% of recurrences in the radiation field, 17.6% of recurrences at the margin of radiation field and 23.5% of recurrences outside the radiation field. The IDH status was associated with patterns of failure. CONCLUSION MRIgOART not only corrected the treatment errors but also optimized the concomitant therapy protocols through daily MRI guidance for brain glioma. The reduction in recurrences within the radiation field and the favorable efficacy of MRIgOART have been demonstrated in patients with HGG. However, further large-scale randomized studies are necessary to validate these findings and further refine treatment strategies.