The goal of this prospective study was to determine the effect of hemoclip use on the size of radiation treatment fields based on a 3-cm margin around a surgical incision alone (field setup 1) vs. a 3-cm margin around the surgical incision plus hemoclips (field setup 2). Forty-seven dogs that underwent surgical resection of a total of 55 soft tissue masses had surgical hemoclips placed at the time of surgery and orthogonal radiographs made immediately postoperatively. Radiation treatment field simulation was done and field areas measured. Additional determinations included number of hemoclips outside of the radiation treatment field based on a margin around the incision alone, hemoclip distance from the incision, and association between incision length and greatest distance of hemoclips from the incision. There was a significant difference in radiation treatment field size using information regarding the location of hemoclips in conjunction with the surgical scar compared with the surgical scar alone for truncal (P=0.0003) vs. extremity tumors (P=0.087). In simulating radiation treatment fields hemoclips were located outside of field setup 1 for the majority of tumors (79%) resected from the trunk but only in a minority of tumors (10.7%) resected from extremity sites. The findings from this study suggest that surgical hemoclips have potential utility in simulation of radiation treatment fields in the postoperative setting.