Evaluation of the Setup Accuracy of a Skin-markerless Positioning Using Surface-guided Radiotherapy in Accelerated Partial Breast Irradiation.

Abstract

Background/aim: Accelerated partial breast irradiation (APBI) is an alternative to whole-breast irradiation in early-stage breast cancer. This study evaluated the setup accuracy of a workflow without skin markers that uses surface-guided radiotherapy (SGRT) in conjunction with clip-based alignment in patients undergoing APBI.

Patients and methods: This study recruited 35 patients who underwent APBI after breast-conserving surgery. Treatment plans were generated with 30 Gy in five fractions. During the treatment period, patients were positioned using AlignRT, intentionally omitting the skin marks. After the initial setup, the position was verified via daily kV images or cone-beam computed tomography, with matching surgical clips serving as the basis. Translational and rotational shifts were recorded, along with the monitoring-on time by AlignRT.

Results: A total of 175 treatment fractions were analyzed. The mean±standard deviation (SD) residual setup error detected via image registration was 0.01±0.18, -0.09±0.22, and -0.04±0.19 cm in the vertical, longitudinal, and lateral axes, respectively. Setup accuracy within 5 mm in all axes was achieved in over 95% of the treatment fractions assessed. During the treatment period, 28% of patients (10 out of 35) maintained position deviations of less than 3 mm in the 3D vector direction. The mean±SD monitoring-on time was 603.3±214.1 s (range=349-1,353 s).

Conclusion: The integration of surface-guided radiation therapy and clip alignment effectively achieved accurate and efficient patient positioning; this can serve as an alternative to traditional skin markers in the external beam APBI workflow.