At present, the development of the accelerator-based irradiation system for boron neutron capture therapy (BNCT) is energetically performed by various groups in the world. Especially in Japan, BNCT using various accelerator-based irradiation systems may be carried out at plural facilities in the near future. Thus, it is the time when BNCT is shifting from a special particle therapy to a general therapy, now. In order to promote this shift, not only the development and improvement for the irradiation system but also the preparation and improvement in the physical engineering and medical physics, such as dosimetry system, etc., is important. Recently, as part of the improvement in the dosimetry method for BNCT, the estimation method of three-dimensional dose distribution using gel detector is focused. In this paper, the principle of BNCT, especially for dose deposition, is introduced, and the studies for gel detector in BNCT are introduced referring to the proceedings of the international symposium for BNCT.