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° in rotation for all patients. The mean and maximum amplitude of SGRT offsets after application of IGRT shifts were ≤(2.6 mm, 1.6°) and (6.8 mm, 4.5°) relative to kV‐2D‐based IGRT; ≤(3.0 mm, 2.6°) and (5.0 mm, 4.7°) 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°). 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. [ABSTRACT FROM AUTHOR]