  Background: The aim of this study was to investigate the role of clinical,
dosimetric and pretherapeutic magnetic resonance imaging (MRI) features for
lesion-specific outcome prediction of stereotactic radiotherapy (SRT) in
patients with brain metastases from malignant melanoma (MBM).
  Methods: In this multicenter, retrospective analysis, we reviewed 517 MBM
from 130 patients treated with SRT (single fraction or hypofractionated). For
each gross tumor volume (GTV) 1576 radiomic features (RF) were calculated (788
each for the GTV and for a 3 mm margin around the GTV). Clinical parameters,
radiation dose and RF from pretherapeutic contrast-enhanced T1-weighted MRI
from different institutions were evaluated with a feature processing and
elimination pipeline in a nested cross-validation scheme.
  Results: Seventy-two (72) of 517 lesions (13.9%) showed a local failure (LF)
after SRT. The processing pipeline showed clinical, dosimetric and radiomic
features providing information for LF prediction. The most prominent ones were
the correlation of the gray level co-occurrence matrix of the margin (hazard
ratio (HR): 0.37, confidence interval (CI): 0.23-0.58) and systemic therapy
before SRT (HR: 0.55, CI: 0.42-0.70). The majority of RF associated with LF was
calculated in the margin around the GTV.
  Conclusions: Pretherapeutic MRI based RF connected with lesion-specific
outcome after SRT could be identified, despite multicentric data and minor
differences in imaging protocols. Image data analysis of the surrounding
metastatic environment may provide therapy-relevant information with the
potential to further individualize radiotherapy strategies.
