ESTRO 2025 - Abstract Book

S706

Clinical - CNS

ESTRO 2025

2604

Digital Poster Stereotactic Radiosurgery of Brain Metastases from Cancers that Rarely Metastasize to the Central Nervous System Senay MUTAF Radiation Oncology, 1. Acıbadem University School of Medicine, Istanbul, Turkey Purpose/Objective: Brain metastases are the most common type of brain tumor, with primary sources including lung, breast, melanoma, and renal cell carcinoma. Other cancers have a lower incidence of brain metastasis. This study aims to evaluate metastases from cancers that rarely metastasize to the central nervous system, including head and neck, genitourinary, gynecological, gastrointestinal, and other cancers. This study investigates local control rates, overall survival, and dosimetric parameters following stereotactic radiosurgery (SRS). Material/Methods: Between 2009 and 2023, 47 patients (201 lesions) with a primary tumor that rarely causes brain metastasis, out of a total of 1294 patients treated for brain metastasis at our clinic, were included in the study. Local control (LC) and overall survival (OS) were assessed using Kaplan-Meier method, and prognosis was analyzed using log-rank test based on tumor types and dosimetric factors. Results: The median follow-up time was 20 months (range: 0-140), with a median age of 53 years (range: 16-83). 53.1% of patients were female. Gastrointestinal cancer was the most common primary cancer (38.3%), with rectal cancer being the most frequent (7 patients). Other cancer types included head and neck (23.1%), gynecological (19.1%), genitourinary (12.8%), and others (8.5%). Only three patients had synchronous brain metastases, while 93.6% had metachronous metastases. Six patients underwent metastasectomy, and five received whole-brain radiotherapy. A total of 76 radiation treatments were administered, with 70.2% receiving stereotactic radiosurgery (SRS) once and 6.4% receiving SRS five times. The median number of fractions was one (range: 1-7), with a median dose of 20 Gy per fraction (range: 4-26 Gy). The total median radiotherapy dose was 20 Gy (range: 14-35 Gy), with a median biological effective dose (BED10) of 60 Gy (range: 28-93.6 Gy). The median overall survival (OS) was 89.9 months, with 30 months for gastrointestinal tumors and 13.9 months for gynecological tumors. No significant survival difference was found between cancer types, and the median survival from brain metastasis development was 30 months. Local recurrence occurred in 8% of cases, with local control rates of 90.3% at 1 year and 86.2% at 2 years. Five lesions developed necrosis at a median of 3.2 months, with no significant correlation between dose and necrosis. Conclusion: The incidence of brain metastases from cancers that rarely spread to the central nervous system has increased with advances in early treatment strategies. CyberKnife stereotactic radiosurgery (SRS) offers an effective treatment, providing high local control rates.

Keywords: Brain metastases, rare cancer, SRS