ESTRO 2025 - Abstract Book

S688

Clinical - CNS

ESTRO 2025

Conclusion: Anlotinib combined with radiotherapy is efficacious and well-tolerated and might be a treatment option for newly diagnosed malignant brain stem glioma in adults.

Keywords: Malignant brainstem glioma, anlotinib, adults

2024

Digital Poster A representative pattern for radiation-induced cerebral contrast enhancements post intensity modulated proton therapy treatment Jen Yu 1,2 , Omer Gal 1,2 , Alonso Gutierrez 1,2 , Matthew Hall 1,2 , Andrew Wroe 1,2 , Minesh Mehta 1,2 , Robert Press 1,2 , Rupesh Kotecha 1,2 1 Radiation Oncology, Miami Cancer Institute at Baptist Hospital Miami, Miami, USA. 2 Radiation Oncology, Florida International University, Miami, USA Purpose/Objective: For patients with primary brain tumors treated with intensity modulated proton therapy (IMPT), radiation-induced cerebral contrast enhancement (RICE) has been observed but is not well understood. In this study, we aim to establish a representative pattern by incorporating dosimetric, radiobiologic, and spatial aspects of RICE-identified lesions to inform IMPT treatment planning. Material/Methods: IMPT plans and subsequent imaging studies of 136 patients with primary brain tumors treated between 2017 to 2023 to a minimum prescription dose of 50.4 Gy RBE (median 54, range 50.4-75 in 30 fractions) with at least 1 year of follow-up were evaluated. IMPT plans typically used 3 beams and were robustly optimized to clinical target volume (CTV). For centrally located CTVs, bilateral symmetric beams were normally used whereas for eccentrically located CTVs, ipsilateral asymmetric beams entering closer to the CTV were used. Physical dose, dose averaged LET d , locations, ventricle involvement and beam geometry for RICE were analyzed. Un-paired t-test was used to evaluate statistical significance. Results: Among 136 patients 36 patients were identified developed RICE-lesions and there was total 73 lesions. Compared with 100 non-RICE patients, RICE patients received higher mean dose to CTV and hot spot dose to ventricles, 54.4 and 51.2 Gy vs. 50.8 and 44, respectively ( p=0.008 and 0.01 ). LET d values were similar between non-RICE and RICE patients (Table 1). Among 73 RICE-lesions, 56 (77%) occurred in eccentrically located CTVs with asymmetric beams resulting in higher mean LET d values in RICE regions compared to symmetric beams (3.2 vs. 2.8 keV/µm, p=0.017 ). Most RICE-lesions (54, 74%) occurred along the CTV border ( B ); a majority (50, 68%) occurred within or close to the Bragg peak distal end area, where LET d ( L ) values are elevated, resulting in higher mean LET d in RICE-lesions than CTVs (3.1 vs. 2.6 keV/µm, p<0.001 ). Lesions were most prevalent (56, 77%) within a 1 cm expansion of ventricles ( V ), receiving lower physical dose than those away from ventricles (49.1 vs. 54.4 Gy, p=0.004 ). Almost all RICE-lesions (70, 96%) occurred within 1 cm expansions of the respective CTVs and therefore received similar doses ( D ) as CTVs (Figure 1).