• World Neurosurg · Feb 2017

    Choosing a prescription isodose in stereotactic radiosurgery for brain metastases: Implications for local control.

    • Kara D Romano, Daniel M Trifiletti, Allison Garda, Zhiyuan Xu, David Schlesinger, William T Watkins, Brian Neal, James M Larner, and Jason P Sheehan.
    • Department of Radiation Oncology, University of Virginia, Charlottesville, Virginia, USA. Electronic address: kara.e.downs@gmail.com.
    • World Neurosurg. 2017 Feb 1; 98: 761767.e1761-767.e1.

    ObjectiveStereotactic radiosurgery (SRS) achieves excellent local control (LC) with limited toxicity for most brain metastases. SRS dose prescription variables influence LC; therefore, we evaluated the impact of prescription isodose line (IDL) on LC after SRS.MethodsA retrospective analysis of patients with brain metastases treated on a Gamma Knife platform from 2004 to 2014 was conducted. Clinical, toxicity, radiographic, and dosimetric data were collected. Cox proportional hazards regression was used to determine progression-free survival (PFS) and competing risks analysis was used to determine predictive factors for LC.ResultsA total of 134 patients with 374 brain metastases were identified with a median survival of 8.7 months (range, 0.2-64.8). The median tumor maximum dimension was 8 mm (range, 2-62 mm), median margin dose was 20 Gy (range, 5-24 Gy), and 12-month LC rate was 88.7%. On multivariate analysis, PFS improved with increasing IDL (P = 0.003) and decreased with non-non-small-cell lung cancer histology (P = 0.001). Margin dose, tumor size, conformality, and previous whole-brain irradiation failed to independently affect PFS. When adjusting for death as a competing risk, the cumulative likelihood of LC improved with higher IDL (P = 0.04). The rate of SRS-induced radiographic and clinical toxicity was low (16.6% and 1.5%, respectively), and neither was affected by IDL.ConclusionsOur results confirm that SRS for brain metastases results in favorable LC, particularly for patients with smaller tumors. We noted that dose delivery to a higher prescription IDL is associated with small but measurable improvements in LC. This finding could be related to higher dose just beyond the radiographically apparent tumor.Copyright © 2016 Elsevier Inc. All rights reserved.

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