In this paper, computational dosimetry studies for gadolinium-157 neutron capture therapy (157GdNCT) were carried out using MCNP Monte Carlo code, and the total equivalent dose rate was calculated in a Snyder head phantom with convenient and more accurate methods compared to the previous methods. The potential effectiveness of such therapy was assessed by calculating the therapeutic ratio based on the calculated dose distribution. The total neutron kerma factor for 157Gd was calculated according to the latest nuclear data. The 157Gd dose was calculated by kerma approximation and also directly by 157Gd capture reactions. The kerma of 157Gd photons was calculated in tumor and compared with the photon dose calculated from the transport of the produced electrons. The results reveal that, due to the severe neutron flux depression and high photon production in the tumor, the kerma approximation does not properly estimate the 157Gd dose and dose of 157Gd photons in a small-size tumor. Increasing the size of the tumor, the 157Gd kerma without considering neutron flux depression and photon kerma approach the dose of 157Gd and photons, respectively. If 157Gd is incorporated into the nucleus of the cancer cells, the therapeutic ratio of 157GdNCT will be greater than one and 157Gd might, therefore, be a good candidate for neutron capture therapy.

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