Investigation of patient characteristics associated with setup errors in intensity-modulated radiotherapy after breast-conserving surgery

Abstract

Background and purpose: Intensity-modulated radiation therapy (IMRT) is a widely used radiotherapy technique in whole breast irradiation. Therefore, planning target volume (PTV), with appropriate margins from clinical target volume (CTV), would adequately account for the setup uncertainty. However, it is still controversial regarding whether the protocol-required margin around the CTV adequately accounts for setup inaccuracies. The aim of this study was to determine the impacts of patient characteristics on the magnitude of geometric setup errors in patients with breast cancer and to obtain individualized PTV margins. Methods: A total of 97 patients treated with IMRT after breast-conserving surgery in Fudan University Shanghai Cancer Center from January 2019 to December 2019 were reviewed. Cone-beam computed tomography (CBCT) scan records were used to analyze setup errors. The impacts of patient characteristics on setup errors were also analyzed, including age, tumor location, body mass index (BMI), chest circumference and breast volume. Population in the two groups was compared in terms of distribution of the median patient characteristics, and individualized PTV margins were obtained. Results: The BMI, chest circumference and breast volume showed moderate positive correlation with superior-inferior (Pearson=0.40, P<0.01), superior-inferior (Pearson=0.43, P<0.01), and right- left directions (Pearson=0.42, P<0.01), respectively. Meanwhile, there were significant differences in setup errors of superior-inferior direction (t=-3.923, P=0.001; t=-5.182, P=0.001; t=-2.712, P=0.008) among the three groups, and significant differences were  also observed in setup errors of left-right direction between the chest circumference and breast volume groups (t=-2.124, P=0.036; t=-3.550, P=0.001). When dividing patients into two groups on the basis of median value of BMI, chest circumference, breast volume and the margin in left-right, superior-inferior and anterior-posterior directions were 3.1-4.5, 4.6-8.0 and 4.9-5.3 mm, respectively. Conclusion: Patient characteristics such as BMI, chest circumference and breast volume were significantly correlated with geometric setup errors. The individualized PTV margins were recommended to adequately compensate for the setup variation detected according to patient characteristics.

Keywords

• patient characteristics| breast neoplasm| radiotherapy|cone-beam computed tomography|setup error