Recent dosimetric tests with the NRG IROC suggested that approximations in analytic dose algorithms on commercial proton planning systems may over predict dose in distal regions of the beams. These findings suggest that the resulting underdosing may lead to recurrences in distal regions of the target. The purpose of this study is to determine if local recurrence is more frequent at the distal region when all beams enter from one side of the chest without an opposing beam. Patients who were treated with proton beam therapy (PBT) on a prospective randomized trial comparing intensity-modulated radiation therapy (IMRT) versus passively scattered proton therapy (PSPT) and developed LR of the tumor (defined as tumor recurring within the PTV) were included in this study. The recurrent tumors were delineated on diagnostic images and registered with the planning CTs and the dose distributions. The locations of the LRs were mapped and divided into two groups based on the hinge beam angle of <=90-degrees versus >90-degrees. We utilized two independent sample Wilcoxon test to compare the LRs in the distal regions between the two groups. A total of 84 patients (41 female and 43 male) underwent PBT, with a median age was 68 years (range, 39-80), mostly white (90.7%). The median radiation dose was 66Gy (range, 60-74Gy). 26 were in <=90-degree-group and 58 patients were in >90-degree-group. There were 5 distal LRs (19.2%) in <=90-degree group and 6 distal LRs (10.3%) in >90-degree group (p <0.001). Our result suggests an association between the beam angle arrangement and distal local recurrence resulting from the limitations of the dose calculation algorithms. The strategy of using opposing beams or wide beam angle in PBT planning should be considered under the existing proton planning system algorithm. Recurrences should be investigated further using more advanced dose calculation techniques (viz. Monte Carlo).