Purpose: External beam accelerated partial breast irradiation requires accurate localization of the target volume for each treatment fraction. Using the concept of target registration error (TRE), the performance of several methods of target localization was compared.
Methods and materials: Twelve patients who underwent external beam accelerated partial breast irradiation were included in this study. TRE was quantified for four methods of image guidance: standard laser-based setup, kilovoltage imaging of the chest wall, kilovoltage imaging of surgically implanted clips, and three-dimensional surface imaging of the breast. The use of a reference surface created from a free-breathing computed tomography scan and a reference surface directly captured with three-dimensional video imaging were compared. The effects of respiratory motion were also considered, and gating was used for 8 of 12 patients.
Results: The median value of the TRE for the laser, chest wall, and clip alignment was 7.1 mm (n=94), 5.4 mm (n=81), and 2.4 mm (n=93), respectively. The median TRE for gated surface imaging based on the first fraction reference surface was 3.2 mm (n=49), and the TRE for gated surface imaging using the computed tomography-based reference surface was 4.9 mm (n=56). The TRE for nongated surface imaging using the first fraction reference surface was 6.2 mm (n=25).
Conclusions: The TRE of surface imaging using a reference surface directly captured with three-dimensional video and the TRE for clip-based setup were within 1 mm. Gated capture is important for surface imaging to reduce the effects of respiratory motion in accelerated partial breast irradiation.