2674 - A Multi-Institutional Prospective Observational Study of Linear Accelerator-Based Single-Isocenter Stereotactic Irradiation for Multiple Brain Metastases

08:00am - 09:00am PT

Hall F

Screen: 9

POSTER

Presenter(s)

Megumi Uto, MD, PhD - Kyoto University Graduate School of Medicine, Kyoto, Kyoto

M. Uto¹, S. Itasaka², Y. Negoro³, K. Sakai², K. Fujii², H. Hanazawa², Y. Tsutsumi², K. Ogura³, D. Torizuka¹, and T. Mizowaki⁴; ¹Department of Radiation Oncology and Image-Applied Therapy, Graduate School of Medicine, Kyoto University, Kyoto, Japan, ²Department of Radiation Oncology, Kurashiki Central Hospital, Kurashiki, Japan, ³Department of Radiation Oncology, Japanese Red Cross Wakayama Medical Center, Wakayama, Japan, ⁴Department of Radiation Oncology and Image-Applied Therapy, Graduate School of Medicine, Kyoto University, Kyoto, Kyoto, Japan

Purpose/Objective(s): Stereotactic radiosurgery is used in daily clinical practice as a treatment option for patients with multiple brain metastases, as established by the JLGK0901 trial. A new irradiation method, linear accelerator (LINAC)-based single-isocenter stereotactic irradiation (SISTI), realized stereotactic irradiation beam deliveries in short treatment time. This multi-institutional, prospective, observational study was conducted to evaluate the efficacy and safety of SISTI for the treatment of multiple brain metastases.

Materials/Methods: Based on the JLGK0901 trial, patients who fulfilled the following criteria were included in this study: (1) age =20 years; (2) malignant solid tumors (excluding small cell lung cancer and malignant lymphoma) as primary tumors and metastases; (3) between 2 and 10 brain metastases on Gd contrast-enhanced MRI; (4) gross tumor volume (GTV) =10 cm³ with maximum diameter =3 cm; (5) total GTV =15 cm³; (6) performance status (PS) 0, 1, or 2, or PS 3 due only to neurological symptoms caused by the tumor; (7) no meningeal dissemination; and (8) no history of craniotomy or intracranial radiation therapy.

A total of 45 patients with 158 lesions were enrolled between May 2020 and December 2022. The median age was 72 years (range, 48-87), with 25 males and 34 lung cancers, two cases each of breast and colorectal cancer, and seven with other histologies. The median PS was 1, the median Karnofsky Performance Status score was 90, and extracranial lesions were uncontrolled in 31 cases. Among 31 patients with lung adenocarcinoma, 13 had EGFR, ALK, or ROS-1 gene mutations.

Results: The median number of planning target volumes was 3 (range 2-8), and the prescribed SISTI dose was 20-30 Gy in 1-5 fractions.

The median follow-up and overall survival (OS) were 13.0 months (range, 1.5-51.5) and 14.1 months [95% confidence interval (CI), 9.6-NA], respectively, and OS rates at 6 and 12 months were 82.2%, 54.3%, respectively. There was no significant difference in overall survival between the group with 2 to 4 brain metastases and the group with 5 to 10 brain metastases (20.8 months vs. 11.7 months, p=0.125).

The median intracranial progression-free survival (ICFS) was 6.4 months (95% CI, 5.3-8.1), and ICFS rates at 6 and 12 months were 62.2% and 26.7%, respectively.

Local recurrence was observed in nine lesions in six patients, with cumulative local recurrence rates at 6 and 12 months of 0% and 4.5% per case, and 0% and 2.6% per lesion, respectively. No significant correlation with local recurrence was found for BED10, BED12, GTV volume or distance between lesions and isocenter.

Regarding adverse events grade =3, one case of grade 3 cerebral edema was noted as a late toxicity.

Conclusion: Local control and adverse event rates were satisfactory, supporting the efficacy and safety of SISTI using LINAC.