Stereotactic radiotherapy (SRT) is being widely accepted as a treatment of choice for patients with a small number of brain metastases and an acceptable size, allowing a better target dose conformity resulting in high local control rates and better sparing of organs at risk. Currently, imaging for such a delivery technique requires both a recent magnetic resonance imaging (MRI) brain study for volume definition and a computed tomography (CT) scan for SRT planning. An MRI-only workflow could reduce the risk of misalignment between the two imaging modalities and shorten the delay of planning. Given the absence of a calibrated electronic density on MRI, the investigators aim to assess the equivalence of synthetic CTs generated by a generative adversarial network (GAN) for planning in the brain SRT setting.

Inclusion Criteria:

• age ≥ 18 years old
• SRT treatment for one or more brain metastasis(ses)
• brain MRI and planning CT scans realized less than 14 days prior to the treatment delivery

Exclusion Criteria:

• MRI's field of view (FOV) judged insufficient for tumour(s) and OAR visualization

Restrospective inclusion of all patients treated with intra-cranial SRT for brain metastases from 2014 to 2018 in our single institution

All collected data that underlie results in a publication.

Data will be available beginning 2 months and ending five years following the final study report completion.

Data access request will be reviewed by the internal committee of Brest University Hospital. Requestor will be required to sign and complete a data access agreement.