Proton Reirradiation for High-Risk Recurrent or New Primary Breast Cancer

Abstract

Radiotherapy is an integral component of multidisciplinary breast cancer care. Given how commonly radiotherapy is used in the treatment of breast cancer, many patients with recurrences have received previous radiotherapy. Patients with new primary breast cancer may also have received previous radiotherapy to the thoracic region. Curative doses and comprehensive field photon reirradiation (reRT) have often been avoided in these patients due to concerns for severe toxicities to organs-at-risk (OARs), such as the heart, lungs, brachial plexus, and soft tissue. However, many patients may benefit from definitive-intent reRT, such as patients with high-risk disease features such as lymph node involvement and dermal/epidermal invasion. Proton therapy is a potentially advantageous treatment option for delivery of reRT due to its lack of exit dose and greater conformality that allow for enhanced non-target tissue sparing of previously irradiated tissues. In this review, we discuss the clinical applications of proton therapy for patients with breast cancer requiring reRT, the currently available literature and how it compares to historical photon reRT outcomes, treatment planning considerations, and questions in this area warranting further study. Given the dosimetric advantages of protons and the data reported to date, proton therapy is a promising option for patients who would benefit from the added locoregional disease control provided by reRT for recurrent or new primary breast cancer.

Keywords: breast cancer; proton therapy; radiation therapy; reirradiation.

Figure 1

Representative axial radiation plan images of a female patient with a primary diagnosis of cT2N0M0 left breast cancer status post neoadjuvant chemotherapy followed by left total mastectomy and axillary lymph node dissection, ypT2N2aM0, followed by comprehensive post-mastectomy radiotherapy (RT) to the left chest wall (CW) and regional lymph node (LN) basins to 50 Gy in 25 fractions, then 7.4 years later with left CW recurrence s/p excision with high-risk features (skeletal muscle and fibroadipose tissue invasion, positive surgical margins, lymphovascular invasion), who received reirradiation to the left CW and regional LN basins. (A) Initial photon radiation plan, (B) cumulative initial photon and reirradiation proton plan, and (C) cumulative initial photon and reirradiation volumetric-modulated arc therapy (VMAT) plan. Colorwash: low dose (blue) = 1000 cGy to DMax (red).