RSI: A Novel Biomarker Predicts RT Therapeutic Benefit in Breast Cancer

Abstract

rotational movements (degrees) in pitch, roll, and yaw were recorded and analyzed. For lung, liver and spine SBRT patients the mean ± SD absolute setup errors for the first CBCTwere: 3.1 ± 2.6 mm, 3.4 ± 2.9 mm, 2.2 ± 1.9 mm, 0.77 ± 0.57, 0.85 ± 0.67, and 0.70 ± 0.55. For second CBCT the mean ± SD absolute immobilization errors were: 0.4 ± 0.5 mm, 0.5 ± 0.5 mm, 0.5 ± 0.7 mm, 0.23 ± 0.29, 0.33 ± 0.35, and 0.22 ± 0.28. For third CBCT, the mean ± SD absolute immobilization errors were: 0.4 ± 0.6 mm, 0.6 ± 0.7 mm, 0.6 ± 0.8 mm, 0.23 ± 0.27, 0.29 ± 0.32, and 0.21 ± 0.26. For fourth CBCT, the mean ± SD absolute immobilization errors were: 0.3 ± 0.4 mm, 0.6 ± 0.8 mm, 0.4 ± 0.6 mm, 0.23 ± 0.30, 0.25 ± 0.3, and 0.19 ± 0.24. The magnitude of setup errors after first CBCT was significantly higher than the immobilization errors (p 0.0001). The immobilization errors after second to fourth CBCTs were submm with no significant difference between them. The data was similar for all SBRT sites. There was no difference in setup or immobilization errors with or without the use of abdominal compression during SBRT. The mean time interval from the first to the fourth CBCT was 38 minutes (SD 7 minutes) (range, 29-63 minutes). Conclusions: These data demonstrate that during SBRT: (1) Image guidance using first CBCT is required for accurate target localization by minimizing setup errors; and (2) the BodyFix, vacuum sleeve and HexaPod system facilitates good immobilization with submm 6 conformal positioning accuracy. This system is user friendly and accurate even in centers like ours with no prior SBRT experience.