Central Nervous System

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MO_5_2580 - Dose-Reduced Stereotactic Radiosurgery for Brain Metastases in the Era of CNS-Penetrating Systemic Therapies

Monday, October 22
10:45 AM - 12:15 PM
Location: Innovation Hub, Exhibit Hall 3

Dose-Reduced Stereotactic Radiosurgery for Brain Metastases in the Era of CNS-Penetrating Systemic Therapies
A. J. Huang, K. E. Huang, R. J. Kumar, A. Goel, N. Harandi, M. C. Rounsaville, R. E. Abendroth, and J. W. Lee; California Pacific Medical Center, San Francisco, CA

Purpose/Objective(s): In the era of CNS-penetrating systemic therapies such as checkpoint inhibitors and small molecule inhibitors, higher intracranial control rates as well as higher rates of radionecrosis have been reported due to the radiosensitization effects of these systemic therapies. We wished to determine if dose-reduced SRS could achieve adequate control rates while minimizing the risk of symptomatic radionecrosis.

Materials/Methods: Our institution implemented a dose-reduced SRS regimen, typically 18Gy in 1fx for 1-3 lesions all <1 cm, and 18Gy in 2fx for >3 simultaneously treated lesions, with lesions all <2 cm. For larger lesions or resection cavities we would prescribe a dose of 21Gy in 3fx or 24Gy in 4fx. Median GTV-PTV expansion was 2mm (range 0-5mm). We reviewed all patients who received SRS for brain metastases between 2014-2015 and documented lesion location, prior radiation, volume, largest single dimension, and if symptomatic radionecrosis occurred. Cancer subtype, systemic therapies, cause of death, and performance status was included as well. Cox proportional hazards models were used to determine factors affecting local control.

Results: From 2014-2015, we treated 242 lesions from 59 patients using dose-reduced SRS. Minimum follow-up was 2-years. The majority of lesions came from a melanoma primary (n=140) while the remainder of the lesions came from a lung (n=61), breast (n=13), gastrointestinal (n=13), ovary (n=7), bladder (n=2), and unknown (n=1) primary. Eighteen lesions were resected before SRS. The majority (85%) of patients received CNS-penetrating systemic therapy concurrently or subsequently after SRS. Local control was 64% at 1-year, and 61% at 2-years. Radionecrosis occurred in 7 lesions (2.9%). The majority of lesions (n=172) were <1cc, and 52 were 1-10cc in volume. The remaining 18 were 10-98cc in volume. On multivariate analysis, maximum single dimension (p=0.018), and prior surgical resection (p=0.03) were independent predictors of local failure. Overall survival was 48% at 1-year and 36% at 2-years. Neurological death was seen in 25% (n=15) patients.

Conclusion: In the modern era of CNS-penetrating systemic therapies, dose-reduced SRS has acceptable local control rates with very low rates of symptomatic radionecrosis.

Author Disclosure: A.J. Huang: None. A. Goel: None. M.C. Rounsaville: None. R. Abendroth: None. J.W. Lee: None.

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