Effect of the Residual Errors on the Dose for Left-Sided Breast Cancer Radiotherapy After Translation Error...

ObjectiveThis study analyzed the dosimetric impact of residual errors (rotational and deformation errors) in left-sided breast cancer radiotherapy after cone-beam CT (CBCT)-based translational errors correction.MethodsTwenty patients treated with intensity-modulated radiotherapy (IMRT) were retrospectively analyzed. Virtual CT images were generated by deforming and registering CBCT images with planning CT images. The accumulated dose was calculated to assess residual errors effects on target and organs at risk (OARs). A phantom test was conducted to evaluate rotational errors impacts.ResultsResults showed significant dose differences: for 4005 cGy, D98 and D95 of the breast (PTV_b) decreased, and mean dose, V30, and V20 of the left lung reduced; for 5000 cGy, D98 of the supraclavicular lymph nodes (PTV_sc) and PTVb, D95 of PTV_b, and mean dose and V20 of the heart differed significantly. Phantom simulations revealed that pitch angles ≤-1.8° and roll/yaw angles >2° caused overdosing in the left lung and heart, with maximum dose differences of 31.89% (heart) and 19.19% (lung) for 4005 cGy, and 26.32% (heart) and 20.92% (PTV_sc) for 5000 cGy.ConclusionResidual errors significantly affect dose distribution despite CBCT-based translational correction. Improved immobilization techniques or 6DOF couch correction are recommended to mitigate rotational errors.