Verification of Surface-Guided Radiation Therapy (SGRT) Alignment for Proton Breast and Chest Wall Patients by Comparison to CT-on-rails and Kv-2D Alignment.

Background: Surface-guided radiation therapy (SGRT) systems have been widely installed and utilized on linear accelerators. However, the use of SGRT with proton therapy is still a newly developing field, and published reports are currently very limited.Purpose: To assess the clinical application and alignment agreement of SGRT with CT-on-rails (CTOR) and kV-2D image-guided radiation therapy (IGRT) for breast treatment using proton therapy.Methods: Four patients receiving breast or chest wall treatment with proton therapy were the subjects of this study. Patient #1 ' s IGRT modalities were a combination of kV-2D and CTOR. CTOR was the only imaging modality for patients #2 and #3, and kV-2D was the only imaging modality for patient #4. The patients' respiratory motions were assessed using a 2-min surface position recorded by the SGRT system during treatment. SGRT offsets reported after IGRT shifts were recorded for each fraction of treatment. The agreement between SGRT and either kV-2D or CTOR was evaluated.Results: The respiratory motion amplitude was <4 mm in translation and <2.0 degrees in rotation for all patients. The mean and maximum amplitude of SGRT offsets after application of IGRT shifts were <=(2.6 mm, 1.6 degrees) and (6.8 mm, 4.5 degrees) relative to kV-2D-based IGRT; <=(3.0 mm, 2.6 degrees) and (5.0 mm, 4.7 degrees) relative to CTOR-based IGRT without breast tissue inflammation. For patient #3, breast inflammation was observed for the last three fractions of treatment, and the maximum SGRT offsets post CTOR shifts were up to (14.0 mm, 5.2 degrees).Conclusions: Due to the overall agreement between SGRT and IGRT within reasonable tolerance, SGRT has the potential to serve as a valuable auxiliary IGRT tool for proton breast treatment and may improve the efficiency of proton breast treatment.