Abstract
Stereotactic radiosurgery (SRS) is an effective and well tolerated treatment for selected brain metastases; however, local recurrence still occurs. We investigated the use of diffusion weighted MRI (DWI) as an adjunct for SRS treatment planning in brain metastases. Seventeen consecutive patients undergoing complete surgical resection of a solitary brain metastasis underwent image analysis retrospectively. SRS treatment plans were generated based on standard 3D post-contrast T1-weighted sequences at 1.5T and then separately using apparent diffusion coefficient (ADC) maps in a blinded fashion. Control scans immediately post operation confirmed complete tumour resection. Treatment plans were compared to one another and with volume of local recurrence at progression quantitatively and qualitatively by calculating the conformity index (CI), the overlapping volume as a proportion of the total combined volume, where 1 = identical plans and 0 = no conformation whatsoever. Gross tumour volumes (GTVs) using ADC and post-contrast T1-weighted sequences were quantitatively the same (related samples Wilcoxon signed rank test = −0.45, p = 0.653) but showed differing conformations (CI 0.53, p < 0.001). The diffusion treatment volume (DTV) obtained by combining the two target volumes was significantly greater than the treatment volume based on post contrast T1-weighted MRI alone, both quantitatively (median 13.65 vs. 9.52 cm3, related samples Wilcoxon signed rank test p < 0.001) and qualitatively (CI 0.74, p = 0.001). This DTV covered a greater volume of subsequent tumour recurrence than the standard plan (median 3.53 cm3 vs. 3.84 cm3, p = 0.002). ADC maps may be a useful tool in addition to the standard post-contrast T1-weighted sequence used for SRS planning.
Highlights
Brain metastases are increasingly common and cause significant morbidity and mortality in patients with solid tumours [1,2,3,4]
Median overall survival was 11.8 months and median time to local recurrence was 8.0 months
In fifteen of seventeen cases neurosurgical resection of a solitary cerebral metastasis was followed by adjuvant whole brain radiotherapy (WBRT) 30 Gy in 10 fractions
Summary
Brain metastases are increasingly common and cause significant morbidity and mortality in patients with solid tumours [1,2,3,4]. J Neurooncol (2017) 131:549–554 patients and diffusion MRI (DWI) sequences are commonly included, historically to distinguish these ring enhancing tumours from abscesses but more recently to aid in differentiating solitary metastases from glioma, for surgical planning and even to predict prognosis [11]. Changes in ADC in the peritumoral brain may precede micro-metastasis appearance in animal models [14] and lower tumour ADC values have been shown to be predictive of earlier recurrence and shorter survival after neurosurgery [12, 13] and SRS [15]. The aim of this study was to investigate whether the addition of an ADC map to a standard post-contrast T1 weighted sequence would aid SRS planning, in terms of increasing the final planned treatment volume or potentially encompassing peritumoral areas where local recurrence subsequently occurred
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