Local recurrent and advanced breast cancer (including inflammatory breast cancer type) is one of the most difficult conditions to cure, and there is a need for a new therapy. If sufficient boron compound can be targeted to the tumor, boron neutron capture therapy (BNCT) can be applied to local recurrent and advanced breast cancer. In this study, we performed preliminary dosimetry with a phantom model of the mammary gland at the Institute for Integrated Radiation and Nuclear Science, Kyoto University (KURNS), and a feasibility dosimetry with JAERI Computational Dosimetry System (JCDS) at the JRR4 reactor of the Japan Atomic Research Institute. Preliminary dosimetry on the phantom model was performed with a thermal neutron irradiation (OO-0011 mode) on a LiF collimation at KURNS. The thermal neutron flux was 5.16 × 108 cm−2 s−1 at the surface of phantom. The blood boron concentration is estimated to be 30 ppm; tumor boron concentration is also estimated to be 90 ppm according to a tumor/blood ratio of 3 and a skin/blood ratio of 1.2. The weighted dose Dw to the tumor is estimated to be 47 Gy/h, and the weighted dose Dw to the skin is 12.4 Gy/h. In the case of recurrent breast cancer, we performed the feasibility estimation on a 3D construction of the tumor according to the MRI images of a patient with epithermal neutron mode at JRR4. The blood boron concentration (ppm) and tumor/normal tissue ratio were estimated to be 24 and 3.5, respectively. The weighted dose Dw to the skin is restricted to 10 Gy/h. The maximum weighted dose Dw to the tumor, the minimum weighted dose Dw to the tumor, and the mean weighted dose Dw to the tumor are 64.3, 16.6, and 46.5 Gy, respectively, for half an hour’s irradiation. We also evaluated the tangent irradiation technique and en face technique. In this study, we showed the possibility to apply BNCT to local recurrent and advanced breast cancer. We can irradiate tumors selectively and safely as possible, reducing the effects on neighboring healthy tissues.