Proton therapy for locally advanced breast cancer: A systematic review of the literature

Abstract

Background: Radiation therapy plays a major role in the management of adjuvant breast cancer with nodal involvement, with an iatrogenic increase of cardio-vascular risk. Photon therapy, even with intensity modulation, has the downsides of high mean heart dose and heterogeneous target coverage, particularly in the case of internal mammary irradiation. This systematic review of the literature aims to evaluate proton therapy in locally advanced breast cancer.

Material and methods: PubMed was searched for original full-text articles with the following search terms: «Proton Therapy» and «Breast Cancer». On-going trials were collected using the words "Breast Cancer" and "Protons".

Results: 13 articles met the criteria: 6 with passive proton therapy (Double Scattering), 5 with Pencil Beam Scanning (PBS) and 2 with a combination of both. Proton therapy offered a better target coverage than photons, even compared with intensity modulation radiation therapy (including static or rotational IMRT or tomotherapy). With proton therapy, volumes receiving 95% of the dose were around 98%, with low volumes receiving 105% of the dose. Proton therapy often decreased mean heart dose by a factor of 2 or 3, i.e. 1 Gy with proton therapy versus 3 Gy with conventional 3D, and 6 Gy for IMRT. Lungs were better spared with proton therapy than with photon therapy. Cutaneous toxicity observed with double scattering is improved with PBS.

Conclusion: Proton therapy reduces mean heart dose in breast cancer irradiation, probably reducing late cardio-vascular toxicity. Large clinical studies will likely confirm a clinical benefit of proton therapy.

Keywords: Breast cancer; Cardiotoxicity; Heart; Proton therapy; Radiation therapy; Systematic review.