DE-iPTV

The aim of this study is to demonstrate if it is possible to delivering a novel and modern radiotherapy approach (Dose Escalated internal PTV (DE-iPTV)) and to collect health related quality of life in patients whose breast cancer has spread to the brain (brain metastases) at 8 weeks post enrolling into the study. The main questions that have been set out to to answer are: * Is it possible to deliver the novel radiotherapy approach, DE-iPTV? * Is it possible to measure health -related quality of life? * What impact does the novel radiotherapy approach have on: patient's quality of life, control of the brain metastasis (control of the lesion) and steroid use? Participants will: * Receive 5 doses of radiotherapy * Complete weekly quality of life (EQ-5D) assessments and medication (steroid) diaries (via telephone/ postal) until 12 weeks post enrolment * Be reviewed in clinic with up-to-date MRI scans at 8, 12 and 24 weeks post-enrolment * Complete a more detailed HRQoL panel of assessments will be assessed at baseline, 8 weeks, 12 weeks and 24 weeks post enrolment.