Setup Error and Effectiveness of Weekly Image-Guided Radiation Therapy of TomoDirect for Early XXXX .

@entity1 @entity0
Purpose: This study investigated setup error and effectiveness of weekly image-guided radiotherapy (IGRT) of TomoDirect for early @entity0 . Materials and Methods: One hundred and fifty-one breasts of 147 consecutive @entity1 who underwent breast conserving surgery (BCS) followed by whole breast irradiation using TomoDirect in 2012 and 2013 were evaluated. All @entity1 received weekly IGRT. The weekly setup errors from simulation to each treatment in reference to chest wall and surgical clips were measured. Random, systemic, and three-dimensional setup errors were assessed. Extensive setup error was defined as 5 mm above the margin in any directions. Results: All mean errors were within 3 mm of all directions. The mean angle of gantry shifts was 0.6   . The mean value of absolute three-dimensional setup error was 4.67 mm. In multivariate analysis, breast size (OR=2.82, 95% of CI: 1.00-7.90) was a significant factor for extensive error. The largest significant deviation of setup error was observed in the first week of radiotherapy (p<0.001) and the deviations gradually decreased with time. The deviation of setup error was 5.68 mm in the first week and within 5 mm after the second week. Conclusion: In this study, there was a significant association between breast size and significant setup error in @entity0 @entity1 who received TomoDirect. The largest deviation occurred in the first week of treatment. Therefore, @entity1 with large breasts should be closely observed on every fraction and fastidious attention is required in the first fraction of IGRT.
