Evaluation of surface-guided radiation therapy for breast cancer using the Halcyon system

Abstract

Background: This study was conducted to evaluate the efficiency and accuracy of the daily patient setup for breast cancer patients by applying surface-guided radiation therapy using the Halcyon system instead of conventional laser alignment based on the skin marking method. Methods and materials: We retrospectively investigated 228 treatment fractions using two different daily patient setup methods. The accuracy of the residual rotational error of the surface-guided radiation therapy system was evaluated by using an in-house breast phantom. The residual translational error was analyzed using the couch position difference in the vertical, longitudinal, and lateral directions between the reference computed tomography and dailykilo-voltage cone beam computed tomography acquired from the record and verification system. The residual rotational error (pitch, yaw, and roll) was also calculated using an auto rigid registration between the two imagesbased on Velocity. The total setup time, which combined the initial setup time and imaging time, was analyzed to evaluate the efficiency of the daily patient setup for surface-guided radiation therapy. Results: The average residual rotational errors using the in-house fabricated breast phantom for pitch, roll, and yaw were 0.14°, 0.13°, and 0.29°, respectively. The average differences in the couch positions for laser alignment based on the skin marking method were 2.8±1.6 mm, 2.0±1.2 mm, and 2.1±1.0 mm for the vertical, longitudinal, and lateral directions, respectively. For surface-guided radiation therapy, the average differences in the couch positions were 1.9±1.2 mm, 2.9±2.1 mm, and 1.9±0.7 mm for the vertical, longitudinal, and lateral directions, respectively. The rotational errors for pitch, yaw, and roll without the surface-guided radiation therapy approach were 0.32±0.30°, 0.51±0.24°, and 0.29±0.22°, respectively. For surface-guided radiation therapy, the rotational errors were 0.30±0.22°, 0.51±0.26°, and 0.19±0.13°, respectively. The average total setup times considering both the initial setup time and imaging timewere 314 s and 331 s, respectively, with and without surface-guided radiation therapy. Conclusion: We demonstrated that using surface-guided radiation therapy improves the accuracy and efficiency of patient setups in breast cancer patients using the Halcyon system, which has limitations in correcting the rotational offset.