Main Session
Sep 29
PQA 03 - Central Nervous System, Professional Development/Medical Education

2636 - Impact of Time from MRI on Local Control for Fractionated Single Isocenter Zero Margin Radiosurgery for Brain Metastases

08:00am - 09:00am PT
Hall F
Screen: 7
POSTER

Presenter(s)

Luke Moradi, MD Headshot
Luke Moradi, MD - University of Alabama at Birmingham, Birmingham, AL

L. Moradi1, R. A. Popple1, R. Travis1, S. Marcrom2, K. Riley3, J. M. Markert3, C. D. Willey4, M. C. Dobelbower1, H. Boggs5, R. Sullivan6, J. A. Pogue5, and J. B. Fiveash1; 1University of Alabama at Birmingham Department of Radiation Oncology, Birmingham, AL, 2Department of Radiation Oncology,University of Alabama at Birmingham, Birmingham, AL, 3University of Alabama at Birmingham Department of Neurosurgery, Birmingham, AL, 4University of Alabama Birmingham, Birmingham, AL, 5Department of Radiation Oncology, University of Alabama at Birmingham, Birmingham, AL, 6University of Alabama at Birmingham, Birmingham, AL

Purpose/Objective(s): Fractionated Stereotactic Radiosurgery (fSRS) is an established method to treat larger brain metastases with excellent local control and acceptable toxicity. MRI fused with CT simulation provides high resolution imaging which is optimum for target delineation for fSRS planning. Logistical challenges along the treatment planning process may result in delays from imaging to treatment initiation. There is concern that delayed initiation of fSRS >14 days from time of MRI can lead to unrecognized tumor progression and worse local control. The purpose of this study was to retrospectively review the local control of brain metastases treated with fSRS as a function of time from MRI to initiation of fSRS.

Materials/Methods: A retrospective review of 251 patients from 2015 to 2022 was conducted which included 1215 tumors receiving either 9 Gy x 3 fx (27 Gy) or 6 Gy x 5 fx (30 Gy) brain fSRS. MRI was fused with CT simulation for optimum target delineation. IV contrast was administered for CT simulation on all patients unless medically contraindicated. All tumors were treated with a single isocenter Volumetric Modulated Arc Therapy (VMAT) via manual (volumetric modulated arc therapy) or automated (HyperArcTM) treatment planning using 0 mm CTV/PTV margin. All tumors in a plan were treated with a single prescription, typically chosen at physician preference dictated by largest tumor size. Local tumor failure was defined as 25% increase in maximum tumor diameter (minimum 3 mm) or more than scant tumor cells at time of salvage surgery. Local tumor control was calculated using Kaplan-Meier method and Cox Linear Regression. Outcomes were measured on a per-tumor basis.

Results: 925 tumors were treated with MRI’s =14 days old and 286 tumors were treated with MRI >15 days old. Tumor local control for the entire cohort was 93% (±0.010) at one year and 88% (±0.015) at two years. The one-year local control rates among tumors with MRI image =14 days old vs. 15+ days was 92% and 94%, respectively (p = 0.29). As a continuous variable, increased time from MRI was not associated with worse local control (HR 0.97, p = 0.083). Using cox multivariate analysis of tumor histology and time from MRI, the only factor that remained a significant predictor of tumor local control was colon histology (n = 29) (HR 6.4, p <0.001).

Conclusion: In the setting of a contrasted CT simulation scan, increased time between MRI and treatment start did not lead to worse local tumor control when treating brain metastases with fSRS.