Evaluation of the clinical implementation of a tattoo-free positioning technique in breast cancer radiotherapy using ExacTrac

Purpose: Conventionally, tattoos and temporary skin marks are used in patient positioning procedures for breast cancer radiotherapy. However, many patients dislike these marks because their daily lives are affected by them. Therefore, we developed a new positioning technique using ExacTrac (BrainLAB AG, Munich, Germany). This study aimed to evaluate the clinical implementation of a tattoo-free positioning technique for breast cancer radiotherapy using ExacTrac.Methods: We included 35 patients with breast cancer, 14 with tattoo-based positioning and 21 with tattoo-free positioning using ExacTrac. In this ExacTrac-based positioning technique, the patients were aligned around the mamilla of the ipsilateral breast, and 6D registration was performed later at the virtual isocenter, which was placed at the spinal cord. The target displacement relative to the treatment isocenter was identified and then compensated for using robotic couch translations and rotations.The gamma index method analyzes the integrated dose images of the transmitted radiation dose through patients to investigate the irradiation accuracy of the two positioning techniques. The clinical implementation of the ExacTrac-based positioning technique was evaluated by comparing the gamma passing rate of the tattoo-based and ExacTrac-based positioning techniques. Results: The mean gamma passing rates of the tattoo-based and ExacTrac-based positioning techniques were 86.0 +/- 10.2% and 90.9 +/- 6.9%, respectively.Conclusion: The ExacTrac-based positioning technique provided positioning comparable to that of the tattoobased positioning technique. Consequently, the clinical implementation of the tattoo-free positioning technique in breast cancer radiotherapy using ExacTrac was demonstrated.