Tolerance range of breast cancer patients with set?up errors after volume modulated radiotherapy / 中华放射医学与防护杂志

ABSTRACT

Objective To predict the tolerance range of set-up errors in clinical practice by predicting the virtual set-up errors of postoperative radiotherapy patients for breast cancer. Methods A retrospective analysis was made of the patients who underwent radiotherapy after breast cancer surgery in recent 3 years. According to different treatment method, 10 cases of breast cancer after modified radical mastectomy and 10 cases after breast conserving radical mastectomy were selected. The target area was delineated, the volume modulated radiation therapy plan was made, the virtual moving error of the center point of the plan was moved, and the maximum moving error was 5 mm by 1 mm step. After recalculating the dose, the corresponding data including the clinical target areas ( CT ) , CTV ( V50 ) , average heart volume, V20 of the affected lung and CTV volume were recorded. SPSS 19. 0 software was used for statistical analysis, and repeated measurement of variance analysis was used to analyze the changes of the actual dose in the target area after moving the center point. Linear regression analysis method was used to analyze the correlation between the CTV volume and the dose change after the CTV moving midline. Results The virtual set-up error had little influence on the axis direction of the approximate mammary tangent direction, while the vertical direction of the approximate mammary tangent direction had greater influence. After moving more than 3 mm on the vertical axis, the CTV ( V50 ) decreased to below 90％, which was lower than the general requirement for the target area of CTV. Statistical analysis of set-up errors in all directions showed that there was significant difference in dosimetric changes ( F=34. 182, 12. 877, 16. 443, 9. 846, 46. 829, 10. 122, 57. 931, P <0. 05) in all directions except the B direction of left breast set-up errors (P>0. 05). Between breast conserving surgery and modified radical mastectomy, there was little effect on target movement. Through correlation analysis, it was found that the volume of CTV in the target area of breast cancer patients was linearly related to the errors caused by the movement of B, C and B directions of left breast and right breast(F=5. 733, 18. 496, 6. 630, P<0. 05). Conclusions In postoperative radiotherapy for breast cancer, the errors perpendicular to the section of breast should be paid special attention to whether left or right breast. When the error of this direction exceeds 3 mm, CTV is obviously less than V50 below 83. 85％. The effect of set-up error on the dose of CTV was not related to the operation mode of breast cancer and there was no obvious correlation with the volume of the target area.