Breast Radiotherapy Using MR-Linac

Pursuing the aim to reduce long-term treatment-related toxicity, current research in breast radiotherapy focuses on reduction of the target volumes. Adjuvant partial breast irradiation instead of whole breast irradiation already represents a standard option for patients with low-risk breast cancer. Magnetic resonance (MR)-guided radiotherapy performed on an MR-Linac offers improved breast tissue and tumor visibility as well as the possibility of a daily online treatment adaptation. This might allow for a further reduction of the irradiated volumes and facilitate neoadjuvant treatment. In this chapter, we discuss partial breast radiotherapy performed on an MR-Linac, including its rationale, advantages, and challenging aspects, with a focus on neoadjuvant partial breast irradiation.