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.

Brain metastases from breast cancer are a common, and devastating, complication with survival times of 3 - 5 months from diagnosis.

The main treatment approaches to brain metastases are surgery, stereotactic radiosurgery (SRS), and whole brain radiotherapy. However, it is known that most patients with brain metastases receive either whole-brain radiotherapy (WBRT) or no treatment, with relatively low rates of surgery and SRS. Since the commonest treatment in those who do have treatment is WBRT, the local team have developed an approach that is believed to be (possibly) more effective than WBRT. The objective is to evaluate this approach in patients who are not suitable to receive more aggressive treatment and who would otherwise receive WBRT. The local approach involves using a modern radiotherapy planning approach, combined with careful, intra-metastasis dose escalation (Dose Escalated internal PTV (DE-iPTV)) to deliver a higher dose to tumour, while delivering less dose to the brain. The combination of less dose to normal structures and more dose to the lesion will hopefully improve Health-related Quality of Life (HRQoL).

The aim of this study is to demonstrate the feasibility of delivering complex radiotherapy, dose escalated internal PTV (DE-iPTV), and measuring quality of life at 8 weeks post-enrolment for patients with brain metastases from breast cancer who would otherwise receive WBRT. An exploratory blood-based biomarker sample collection and analysis will be completed. Furthermore, linked national cancer data will be used to measure the number of patients currently offered WBRT, including survival costs and hospital admissions, and thus provide a baseline to estimate the impact of this novel approach.

Inclusion Criteria

1. Written (signed and dated) informed consent and be capable of co-operating with treatment and follow-up
2. Adult (aged 16+) patients, resident in the United Kingdom.
3. Histologically confirmed primary breast cancer with brain metastases on MRI imaging
4. The treating oncologist considers whole-brain radiotherapy to be the most suitable treatment outside of the trial.
5. Eastern Cooperative Oncology Group Performance status 0, 1 or 2
6. Able to respond to question about their quality of life, symptoms, and side effects remotely (via telephone assessments
7. Life expectancy from extra-cranial disease >3 months

Exclusion Criteria

1. Leptomeningeal disease
2. "Miliary" pattern of metastases: patients with over 15 metastases are excluded (clinician-based assessment)
3. Cystic metastases
4. Previous whole or partial brain radiotherapy (previous surgery or SRS is acceptable)
5. Plan for hippocampal-sparing whole brain radiotherapy.
6. Unable to give informed consent.
7. Prognosis less than 3 months
8. Pregnant or nursing women
9. Unable to complete a brain MRI and/or known allergy to gadolinium.