PURPOSE: To identify weak points in daily routine use of radiation therapy (RT) for non-metastatic breast cancer patients, particularly when data are lacking or equivocal, a "think tank" of experts met in Assisi. METHODS: Before the meeting, controversial issues on non-metastatic breast cancer were identified and reviewed, and clinical practice investigated by means of an online questionnaire. During the 3-day meeting, topics were discussed in-depth with attendees and potential sponsors that are involved in breast cancer treatment. RESULTS: Three issues were identified as needing further investigation: (1) Regional lymph node treatment in early-stage breast cancer; (2) Combined post-mastectomy RT and breast reconstruction; (3) RT in patients treated with primary systemic therapy. Future research proposals included the following: (1) Participating in appropriately selected on-going clinical trials; (2) Designing new randomized controlled clinical trials and prospective population cohort studies; (3) Setting-up large database(s) to generate predictive response models and detect biomarkers for tailored loco-regional treatments. CONCLUSIONS: It is hoped that the ATTM findings, as described in the present white paper, will stimulate a new generation of radiation oncologists to focus on research in these areas, and that the white paper will become a tool for multidisciplinary groups to help them design research proposals and strategies.