JRSBRT 10.1-2, p. 57-62 (PDF)

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Inter-fraction monitoring of brain metastases resection cavities during fractionated stereotactic radiosurgery on the 0.35 T MRI-Linac
Natalia Lutsik, Karen Chin Snyder, Eyub Y. Akdemir, Alessandro Valderrama, Gregory A. Azzam, Gregory J. Kubicek, Rupesh Kotecha, Parag J. Parikh and Eric A. Mellon

Background: Fractionated stereotactic radiosurgery (fSRS) is a standard treatment for brain metastases resection cavities, but changes in cavities sizes during SRS can affect radiation precision. MRI-guided adaptive radiotherapy (RT) offers per-fraction imaging to visualize and address these changes.

Materials and methods: We analyzed five patients treated with fSRS on a 0.35 T MRI-Linac at three centers, assessing cavity volume changes across 3–5 treatment fractions. Pre-treatment and fractional MRIs were used to evaluate relative changes in planning target volume (PTV index), brain volume pulled into the PTV (migration volume), and PTV Hausdorff distances.

Results: Three of five patients showed >1 ml cavity shrinkage during fSRS. The ranges for PTV index, brain migration volume, and Hausdorff distance were 0.59 to 1.13 (median: 0.85 ± 0.14), −1.57 to 16.53 ml (median: 2.59 ± 4.78 ml), and 2.34 to 9.84 mm (median: 4.30 ± 1.96 mm).

Conclusion: MRI-Linac imaging during fSRS allows adaptive adjustments, potentially reducing toxicity for post-surgical brain metastasis treatment.

Keywords: fractionated stereotactic radiosurgery, brain metastasis, MRI-linear accelerator