Similar treatment plans or similar cases in radiotherapy treatment planning (RTP) databases of senior experienced planners could be helpful or educational for treatment planners who have few experiences of stereotactic body radiotherapy (SBRT). The aim of this study was to investigate the feasibility of beam arrangements determined using similar cases in a RTP database including plans designed by experienced treatment planners. Similar cases were automatically selected based on geometrical features and planning evaluation indices from 81 cases with lung cancer who received SBRT. First, the RTP database was searched for the five most similar cases based on geometrical features related to the location, size, and shape of the planning target volume, lung, and spinal cord. Second, the five beam arrangements of an objective case were automatically determined by registering five similar cases to the objective case with respect to lung regions by means of a linear registration technique. For evaluation of the beam arrangements, five plans were designed by applying the beam arrangements determined in the second step to the objective case. The most usable beam arrangement was selected by sorting the five plans based on 11 planning evaluation indices including tumor control probability and normal tissue complication probability. We applied the proposed two-step method to 10 test cases by using an RTP database of 81 cases with lung cancer, and compared the 11 planning evaluation indices between the original plan and the corresponding most usable similar-case-based plan. As a result, there were no statistically significant differences between the original beam arrangements and the most usable similar-case-based beam arrangements (P > 0.05) in terms of the 10 planning evaluation indices. The proposed method suggested usable beam arrangements with little difference from cases in the RTP database, and thus it could be employed as an educational tool for less experienced treatment planners.