Increasing the dose proved to be effective (fewer biochemical recurrence) in external beam radiotherapy for prostate cancer. Underway attempts to extrapolate this relationship to permanent (low-dose) brachytherapy, although the validity of this extrapolation is still in question. In contrast to external beam radiotherapy, brachytherapy requires the implementation of quality control manipulations based от visualization of actual (rather than planned) source distribution within the prostate and calculation of the actual radiation dose. The main tool for this task is the postimplant dosimetric analysis (PDA), and its most important indicator determining the local focal dose in the target organ - D90. However, satisfactory PDA is not always associated with high rates of disease-free survival, and vice versa, a good disease-free survival sometimes occurs in the "failure" irradiation. In this review the authors present results of clinical studies, including multicenter, describing the situation from different perspectives: one confirm this postulate, others deny that the D90 is one of the most important predictors of disease-free survival with permanent prostate brachytherapy. The analysis of the reasons that explain why some of the recent studies could not find a dose-response relationship for permanent brachytherapy. Despite some limitations, D90 is one of the main parameters for assessing the quality of implantation, it was especially important in the early days of the technique, but still remains very useful for at least a rough comparison of results from different centers.