Set-up error and CTV margin in one-week ultra-hypofractionated whole breast irradiation after breast-conserving surgery based on daily CBCT
10.19401/j.cnki.1007-3639.2025.08.003
- VernacularTitle:基于每日CBCT的乳腺癌术后单周超大分割全乳放疗的位置误差及外扩边界研究
- Author:
Mengxiao WANG
1
;
Wendong FAN
;
Jingjing CAO
;
Jiayi CHEN
;
Gang CAI
;
Lu CAO
Author Information
1. 上海交通大学医学院附属瑞金医院放射治疗科,上海 200025
- Publication Type:Journal Article
- Keywords:
Breast cancer;
Ultra-hypofractionated radiotherapy;
Whole breast irradiation;
Set-up error;
Margin
- From:
China Oncology
2025;35(8):752-760
- CountryChina
- Language:Chinese
-
Abstract:
Background and purpose:Single-week ultra-hypofractionated whole breast irradiation(WBI)after breast-conserving surgery could shorten the treatment duration while ensuring efficacy and safety,making it a viable option for WBI.However,ultra-hypofractionated WBI requires daily image-guided radiotherapy(IGRT),and its impact on setup errors remains unclear.This study aimed to identify factors associated with set-up errors in ultra-hypofractionated WBI guided with daily cone-beam computed tomography(CBCT)and calculate margin expanded from clinical target volume(CTV)to planning target volume(PTV).Methods:This study included patients enrolled in a prospective trial that explored the safety of single-week ultra-hypofractionated WBI(NCT04926766)in Shanghai Ruijin Hospital,which was approved by Shanghai Ruijin Hospital Ethics Committee(No.2020-352).All patients received CBCT1 after positioning.After correcting errors,patients received CBCT2.CBCT3 was conducted after radiotherapy was completed.The translational errors between CBCT1,CBCT2,and plan CT were initial and residual inter-fractional errors.The translational error between CBCT2 and CBCT3 was an intra-fractional error.The PTV margin was calculated according to the van Herk formula.Results:A total of 34 patients were enrolled in this study,and 510 CBCT images were collected.Daily CBCT significantly reduced set-up error in anterior-posterior(AP),superior-inferior(SI)and right-left(RL)directions(initial inter-fractional error vs residual inter-fractional error:AP,2.8 mm vs 0.4 mm;SI,1.6 mm vs 0.5 mm;RL,1.8 mm vs 0.3 mm,all P＜0.001).Higher CTV volume(＞402.5 cm3 vs≤402.5 cm3)was associated with larger residual inter-fractional error(0.5 mm vs 0.3 mm,P=0.023)and intra-fractional error(0.5 mm vs 0.2 mm,P=0.001)in AP direction.Higher CTV volume was also associated with larger residual inter-fractional error in the SI direction(0.6 mm vs 0.5 mm,P=0.037).Higher BMI(＞23.2 kg/m2 vs≤23.2 kg/m2)and larger weight(＞60.0 kg vs≤60.0 kg)were associated with larger intra-fractional error in AP direction:0.7 mm vs 0.2 mm(P＜0.001)and 0.5 mm vs 0.2 mm(P=0.033),respectively.Under guidance with daily CBCT,the recommended margins were 2.3 mm in AP direction,2.8 mm in SI direction,and 2.0 mm in RL direction.However,in patients with CTV volume＞402.5 cm3 and BMI＞23.2 kg/m2,a larger margin was recommended in SI direction:3.1 mm and 3.4 mm,respectively.Conclusion:The 3 mm margin was feasible under guidance with daily CBCT.The CTV to PTV margin should be larger in patients with higher BMI or CTV volume.
