Brain metastases affect approximately 20% to 40% of cancer patients and their incidence has been increasing over time. Early detection, followed by a timely intervention, plays a critical role in mitigating the impact of this condition and significantly increasing the chances of treatment success. The Radiotherapy Follow-Up dataset (RFUds) contains medical images of 44 patients with brain metastases, whose primary tumors have different locations. Each patient was treated with radiotherapy, either with LINAC or Gamma Knife. RFUds consists of several patients with different number of treatments and follow-up sessions and contains pre-treatment NifTI CT and MRI files, along with volumes concerning each of the structures delineated during each treatment planning phase, and MRIs acquired in follow-up sessions. RFUds is derived from an original dataset after processing to enhance contrast and improve image quality. The CT datasets were subjected to windowing and artifact reduction and the MRI datasets were processed using the CLAHE technique. Image registration was performed between CT and MRI datasets to align all data from the same patient. In addition, a document containing the transformation matrix resulting from the image registration process is included for each MRI dataset.