In this study, we evaluate the dose distributions of $^{4}$He and $^{6}$He ion beams under the same irradiation settings by using the Monte Carlo method. For the simulations, we defined a water phantom that which includes three normal regions and one target region for measuring the dose deposition in various regions. In addition, we define the $^{4}$He and the $^{6}$He ion beams with specified parameters. Then, we obtain the distributions of the doses and the tracks of $^{4}$He and $^{6}$He ion beams and calculate the dose deposited in each region. The calculated results show that in the proximal volume, lateral volume, distal volume, and target volume, the dose depositions of the $^{4}$He ion beam are 73.77%, 31.44%, 73.5%, and 98.50% of that of $^{6}$He ion beam. In conclusion, we can say from the aspect of physical dose distribution, that the $^{4}$He ion beam is more ideal than the $^{6}$He ion beam. To more objectively evaluate the therapatic effects of $^{4}$He and $^{6}$He ion beams, in our need experiment-based study, we will consider the biological effects of $^{4}$He and $^{6}$He ion beams.

Keywords: $^{4}$He, $^{6}$He, Monte carlo method