P202] No improvement in kV-MV based setup for breast radiotherapy with optical surface guided correction of arm posture

Abstract

Purpose Optical surface scanning can be used to correct the arm posture in breast radiotherapy. The purpose of this study was to investigate if such arm posture corrections can improve kV-MV based patient setup. Furthermore it was evaluated whether setup based on surface scanning alone would be sufficient. Methods Twenty-one patients without and 19 patients with arm posture correction using an optical surface scanning system (Catalyst and Sentinel, from C-RAD Positioning AB, Uppsala, Sweden) were included. A surface scan was acquired, and patients were subsequently imaged using kV-MV imaging. Required translational shifts were applied to reach the treatment position. The patients were treated and then imaged using cone beam computed tomography CBCT. The setup errors in the two groups (with and without arm correction) were evaluated using the CBCT as ground truth. Based on alignment of the surfaces from treatment to the surface from the CT room the potential treatment positions, had setup been based on surface scanning alone, were calculated. Results Arm posture correction was needed in 86% of the treatment fractions. Correcting the arm posture did not lead to any statistical significant differences in setup errors compared to the group with no arm correction. If patient setup had been based solely on surface scanning statistical significant larger setup errors would have been a result. Conclusions Using an optical surface scanning system for arm posture correction prior to kV-MV imaging in breast radiotherapy was not found to improve the kV-MV based setup. The study suggest that surface based setup can be used for initial setup, but target position should be verified using e.g. kV-MV imaging.