Repeat radiation therapy to the breast using proton therapy following a recurrence of breast cancer

Breast cancer is the most common cancer among women. After breast-conserving surgery, the entire breast is typically treated with radiation to reduce the risk of recurrence. Nevertheless, some patients may experience a recurrence of the tumor in the same breast. Until now, a mastectomy (complete removal of the breast) has often been recommended in such cases, as repeat radiation therapy using conventional methods carries an increased risk of side effects on the skin and surrounding tissue that have already been irradiated. Proton therapy is a novel radiation treatment method with unique physical properties. The protons (positively charged particles) deliver their energy specifically to the tumor area (known as the Bragg peak), thereby better sparing the surrounding healthy tissue than conventional radiation therapy using photons. Proton therapy is already used as a radiation treatment for various types of cancer; however, in Germany, it has not yet been established as a treatment for repeat partial breast irradiation in cases of breast cancer recurrence.

The aim of this study is to investigate the efficacy and tolerability of partial breast irradiation with proton therapy following a repeat breast-conserving surgery. The treatment consists of 15 individual sessions. This is a single-arm study, meaning all patients receive the same treatment. The primary endpoint of the study is the occurrence of severe skin reactions (grade 3 or higher) within the first six months after the start of partial breast irradiation.

Women aged 18 and older with recurrent or newly diagnosed breast cancer in a breast that has already been treated with radiation, who have undergone a repeat breast-conserving surgery, are eligible to participate in this study. Additional eligibility criteria include, among others, that the recurrent tumor is smaller than 3 cm, no lymph nodes are involved, the tumor margins were tumor-free at the time of surgery (R0 resection), and at least twelve months have passed since the last radiation treatment.