Factors affecting the geometry variations of surgical clips in radiotherapy after breast-conserving surgery / 中华放射医学与防护杂志

ABSTRACT

Objective:To investigate the variations and related influencing factors of the volumes, positions, and morphologies of geometries formed by surgical clips in intensity-modulated radiation therapy (IMRT) for whole breasts after breast-conserving surgery.Methods:A retrospective analysis was conducted on 18 patients treated with IMRT from October 2021 to September 2022 after breast-conserving surgery. Set-up errors were obtained by reading the coordinate information of tumor bed surgical clips according to the cone beam CT (CBCT) images at 0, 10, 20, 30, 40, and 50 Gy sequentially. Geometries were constructed using the convex hull program, and the volumes ( Vct and V0-5) of geometries were then calculated based on the localization CT images and the six CBCT images, respectively. The centroid displacements ( D0-5) and degrees of inclusion ( DI0-5) of these geometries were compared. The t-test or rank-sum test was used to analyze the effects of radiation doses on V0-5, D0-5, and DI0-5. The Pearson correlation analysis was conducted to analyze the correlations between D0-5 and corresponding set-up errors in three-dimensional directions, and the correlations of average V0-5 variation ( AV), average D0-5 ( AD), and average DI0-5 ( ADI) with the body mass index (BMI), the volume of a breast ( VB), the breast axial height ( H), and the time interval from surgery to radiotherapy ( T) each. The influences of quadrants ( Q) where geometries are located and states ( S) of geometries adhering to or away from the chest walls on AV, AD, and ADI were analyzed through one-way ANOVA. Results:The differences between D5 and D0, between D5 and D1, and between D5 and D2 were statistically significant ( t = -3.27, -4.52, -3.38, P < 0.05), respectively. The differences between DI5 and DI0, between DI5 and DI1, between DI5 and DI2 were statistically significant ( t = 2.53, 2.70, 2.64, P < 0.05), respectively. D1 and D4 correlated with the set-up errors in the superior-inferior dimension, and D3 correlated with the set-up errors in the left-right dimension ( r = 0.50, 0.56, 0.53, P < 0.05). The AD was related to BMI, VB, and H ( r = 0.54, 0.48, 0.50, P < 0.05). There were statistically significant differences in AV and ADI of geometries away from ( S3) and near ( S2) chest walls ( F = 2.66, 3.83, P < 0.05). The AD differences of geometries between S3 and the state adhering to chest walls ( S1) and between S3 and S2 were statistically significant ( F = 7.46, P < 0.05), respectively. Conclusions:The geometries are relatively constant volumes during whole-breast radiotherapy. However, their positions and morphologies vary greatly in the late course. The volume variation ratios, centroid displacements, and degrees of inclusion of geometries are all affected by the states of their attachments to the chest walls. The centroid displacements correlate with breast morphologies and BMI. The radiotherapy plan modification can be individualized.