Evaluation of the Setup Error using On-Board Imager (OBI) System in Upper Abdominal Cancer

Abstract

Purpose: To study the setup error of patient’s positioning in upper abdominal cancer.

Materials and Methods: Eleven patients with upper abdominal cancer treated by 3D-CRT and IMRT techniques were studied during June 2008 to February 2009. Pre-treatment process began when two images in AP and Lat views of the patient were captured by using the OBI (Onboard Imager) System that attached with the linear accelerator machine. These two images were overlaid with the reference DRR (Digital reconstruction radiograph) of the planning CT (in the same views). As a consequence. the setup or couch position errors compared with the treatment planning values in three directions were calculated by the OBI software. Once the shifts applied, the couch had automatically moved to the right positions before treating the patient.

Results: For 134 OBI sessions. the average errors were 0.18±0.14 cm (0 - 0.7 cm), 0.24±0.22 cm (0-1.0 cm) and 0.21±0.18 cm (0 - 0.7 cm) in vertical (Vrt). longitudinal (Lng) and lateral (Lat) directions respectively. The maximum setup error was 1.0 cm in the Lng direction for a single patient. However. the errors within 0.5 cm in these three directions resulted as 99%, 88%, and 93%.

Conclusion: Most of the setup error values were acceptable within 0.5 cm in the entire directions; Vrt, Lng and Lat. Using OBI system, the patients were typically treated in the same position as mentioned in the treatment planning that helps to increase tumor control probability and decreasing complication rate.