Treatment planning for resected abdominal tumors: Differences in organ position between diagnostic and radiation-planning computed tomography scans

Purpose: To evaluate whether organ location, determined from preoperative diagnostic computed tomography scans (CTs), accurately reflects organ location when patients are positioned for radiation therapy. Methods and Materials: We identified patients with upper abdominal malignancies treated with surgery and/or radiation therapy. Comparisons of organ position relative to fixed bony landmarks were made among preoperative diagnostic CTs, postoperative diagnostic CTs, and radiation-planning CTs. We studied 18 patients who had CTs differing only in scanning technique, 11 patients who had CTs differing only in operative state, and 7 patients with CTs differing in both scanning technique and operative state. Results: For patients with diagnostic CTs and radiation-planning CTs that were either both preoperative or both postoperative, mean organ position, measured relative to a fixed bony landmark, ranged from 1.9 to 3.2 cm superior on radiation-planning CTs compared with diagnostic CTs (p < 0.0001). Mean organ position ranged from 0.9 to 1.7 cm posterior on radiation-planning CTs compared with diagnostic CTs (p ≤ 0.008). Shifts in the right-left direction were small and variable. For patients with pre- and postoperative diagnostic CTs, organ shifts were variable and not significant. Organ shifts for patients with preoperative diagnostic CTs and postoperative radiation-planning CTs were similar to shifts observed for the first group. Conclusions: Relative to bony landmarks, there are superior and posterior shifts in organ position for radiation-planning CTs compared with diagnostic CTs. These shifts should be considered during treatment planning for resected abdominal tumors.