ESTRO meets Asia 2024 - Abstract Book

S102

Interdisciplinary – CNS

ESTRO meets Asia 2024

103

Digital Poster

The clinical outcomes of LINAC based stereotactic radiotherapy for multiple brain metastases

Hikaru Niitsu 1,2 , Yoshio Tamaki 2,3 , Yuichi Hiroshima 1,2 , Reiko Kanuma 2 , Toshiyuki Okumura 2 , Michihisa Kawashima 4 , Kazuya Shinoda 4 , Hideyuki Sakurai 1 1 Department of Radiation Oncology, University of Tsukuba, Tsukuba, Japan. 2 Department of Radiation Oncology, Ibaraki Prefectural Central Hospital, Ibaraki Cancer Center, Kasama, Japan. 3 Department of Radiation Oncology, Fukushima Rosai Hospital, Iwaki, Japan. 4 Department of Radiation Technology, Ibaraki Prefectural Central Hospital, Ibaraki Cancer Center, Kasama, Japan

Purpose/Objective:

Advances in chemotherapy and radiotherapy techniques have expanded the indications for stereotactic radiosurgery and radiotherapy (SRS/ SRT) in treating multiple brain metastases. At our hospital, we introduced the Elements Multiple Brain Mets System (mSRS/ SRT system) developed by Brainlab AG (Munich, Germany) in December 2018, employing the dynamic conformal arc method with a single isocenter. This method has proven efficient, facilitating easy verification and quick execution of SRS/ SRT for multiple brain metastases. This study aims to analyze the clinical outcomes of patients treated with the mSRS/ SRT system for multiple brain metastases.

Material/Methods:

Patients with multiple brain metastases treated with the mSRS/ SRT using Varian Trilogy linac with 5 mm multileaf collimeters between December 2018 to March 2023 were identified from the treatment database. The prescribed dose for the PTV, determined by D95%, was 21 Gy or 18 Gy in a single fraction for lesions with a maximum tumor diameter <= 2 cm. For lesions with a maximum tumor diameter > 2 cm, the prescribed dose was 30 Gy in 3 fractions or 35 Gy in 5 fractions. To differentiate recurrence from necrosis, T1/ T2 mismatch or apparent diffusion coefficient (ADC) values on contrast enhanced magnetic resonance imaging (MRI) was used. Overall survival (OS: per patients) and local control rate (LC: per lesions) were evaluated by the Kaplan-Meier method, and the association with treatment factors was analyzed by log-rank and Cox regression model. Adverse events were evaluated with CTCAE v5.0. This study was approved by ethics committee in our hospital.

Results:

Thirty patients and 133 lesions were included in this study. Median age was 67 years (range: 45-84 years). According to primary lesions, 20 patients were lung cancer, 4 were colon cancer, 3 were breast cancer and 3 were other cancers. Median number of treated lesions were 3 (2-12) and median maximum tumor diameter was 1.11 cm (0.51-2.88 cm). Twenty-two patients, 88 lesions were treated in single fraction and eleven patients, 45 lesions were in multi-fraction. Repeated SRS/ SRT for recurrence outside irradiation field was performed in 6 cases. The median follow-up time was 7.2 months (3.0-52.1 months) in all patients and 21.4 months (4.6-52.1 months) in survival group. The 12-months OS was 46.8% (95%CI: 37.3-56.3%). On univariate analysis for prognostic factor of OS, primary lesions (lung cancer vs others), number of lesions, total tumor volume, presence of chemotherapy before or after SRS/ SRT were significant prognostic factors (p=0.002/ 0.043/ 0.027/ 0.027/ <0.001). On multivariate analysis, presence of chemotherapy after SRS/SRT was the only significant factor (p=0.014). The 12-months LC was 83.8% (95%CI: 79.4-88.2%). On univariate analysis, tumor diameter, fraction size and presence of chemotherapy after SRS/ SRT have significant differences (p=0.005/ 0.002/ 0.001). On multivariate analysis, maximum tumor