This study analyzed the setup error of breast cancer patients in IMRT with DIBH and analyzed the dose distribution due to setup error.
A total of 45 breast cancer cases were divided according to primary site location and breast size. We performed a retrospective clinical analysis including the mean (M), three-dimensional setup displacement error (3-D error), systematic error (Σ), random error (σ). In addition, the re-treatment planning was carried by shifting the setup error from the isocenter at the treatment. Based on this, the dose distribution of PTV and OARs was compared and analyzed.
The mean error value obtained from daily IGRT was within 3 mm in all directions and the rotation error was within 1 degree. There was a correlation of setup errors with breast size. The 3D-errors were 3.1 mm, 3.7 mm and 4.1 mm in small breast volume group, medium breast volume group and large breast volume group, respectively. DVH results showed HI for the PTV difference between standard treatment plan and re-treatment plan of 14.4%. The difference in CI for the PTV was 4%. The difference in D5 and V20 of the ipsilateral lung was 5.6%, 13% respectively. The difference in D5 and V5 of the heart of right breast cancer patients was 6.8%, 8% respectively. The difference in D5, V20 of the heart of left breast cancer patients was 7.2%, 23.5% respectively.
In this study, there was a significant association between breast size and significant setup error in breast cancer patients. In the IMRT with DIBH, large breast size patients will need to be particularly interested in setup. In addition, it is considered that the correction of the setup error using daily IGRT is important because the change in the dose distribution due to setup errors during IMRT is sensitive despite the risk of increased treatment time and increased patient exposure.