Comparison of setup errors between two immobilization methods in prostate cancer radiotherapy based on cone-beam computed tomography
10.19723/j.issn.1671-167X.2025.04.010
- VernacularTitle:基于锥形束CT的前列腺癌放射治疗两种体位固定方式摆位误差比较
- Author:
Jie LIU
1
;
Mingwei MA
1
;
Qing'an WANG
1
;
Ming SHI
1
;
Jinpeng YIN
1
;
Zhanping WANG
1
;
Jingtao SHEN
1
;
Xianshu GAO
1
Author Information
1. 北京大学第一医院放射治疗科,北京 100034
- Publication Type:Journal Article
- Keywords:
Prostate cancer;
Cone-beam computed tomography;
Setup error;
Immobilization;
Thermo-plastic mask
- From:
Journal of Peking University(Health Sciences)
2025;57(4):692-697
- CountryChina
- Language:Chinese
-
Abstract:
Objective:To analyze and compare the interfractional setup errors between two body posi-tioning fixation methods(lithotomy position with carbon fiber full-body fixation frame vs.conventional carbon fiber body fixation frame combined with thermoplastic membrane)in radical radiotherapy for pros-tate cancer,and to calculate the clinical target volume(CTV)to planning target volume(PTV)margin(MPTV)for both methods to optimize immobilization techniques and radiotherapy workflows.Methods:A retrospective analysis was conducted on 37 consecutive patients who underwent radical prostate radio-therapy at Peking University First Hospital between August 2021 and March 2023.The patients were di-vided into two groups based on the immobilization method:Group A(18 patients,450 CBCT image sets)used a carbon fiber whole-body fixator in the lithotomy position,while Group B(19 patients,461 CBCT image sets)used a conventional carbon fiber fixator combined with a thermoplastic mask.All the patients underwent daily cone-beam computed tomography(CBCT)image guidance.Bone registration combined with manual registration was used to obtain the setup error data in the left-right(X),cranio-caudal(Y)and anterior-posterior(Z)directions.The positioning errors of the two groups were compared by using the independent sample t-test,the Mann-Whitney U test and the chi-square test.The average positioning error,systematic positioning error(Σ)and random positioning error(δ)were calculated,and the CTV-PTV extension distance was calculated by using the(MPTV=2.5Σ+0.7δ).Results:The analysis of the setup errors in the three-dimensional direction showed significant differences between the two groups(all P＜0.01).Specifically,the median(quartile)absolute values of the errors in the X,Y,and Z di-rections of group A were[0.40(0.20,0.70)cm,0.50(0.30,0.80)cm,and 0.35(0.20,0.60)cm],respectively.In group B,the corresponding values were significantly reduced to[0.20(0.10,0.40)cm,0.40(0.20,0.70)cm and 0.20(0.10,0.40)cm].The results of Mann-Whitney U test showed that the differences in each direction were highly statistically significant(X:z=-6.86;Y:z=-2.76;Z:z=-5.71).The cumulative distribution ratio of the setup error displacement within 0.5 cm in the X,Y,and Z directions in group A and group B were 297(66.0％)and 408(88.5％)(P＜0.01),250(55.6％)and 285(61.8％)(P=0.055),308(68.4％)and 391(84.8％)(P＜0.01),re-spectively.The CTV-PTV margins in three directions were X 0.66 cm in group A and 0.35 cm in group B;Y0.67 cm and 0.45 cm;Z 0.54 cm and 0.42 cm.Conclusion:Conventional carbon fiber human body fixator combined with thermoplastic film can significantly reduce the setup error.However,the car-bon fiber whole-body fixator in the lithotomy position demonstrated larger setup errors in the X,Y,and Z directions compared with the conventional fixator combined with a thermoplastic mask,indicating the need for further workflow optimization.Given that the lithotomy position is essential for transperineal ultrasound-guided techniques,further research and improvements are required to achieve higher positioning accuracy.
