Background/Purpose Sex has been shown to influence the prognosis of various cancers. However, the impact of sex on setup accuracy in radiotherapy for rectal cancer has not been reported. To address this gap, we conducted a large-scale real-world study to analyze the influence of sex on setup accuracy and planning target volume (PTV) margins in rectal cancer patients undergoing radiotherapy. Materials and Methods We retrospectively collected data from rectal cancer patients treated with volumetric modulated arc therapy (VMAT) between January 2020 and December 2023. Patients were divided into male and female groups based on sex. Setup errors were compared between the two groups for the overall body, coccyx, and the fifth lumbar vertebra (L5) as regions of interest (ROIs). The PTV margins(With regard to setup errors alone)for each ROI were calculated using the van Herk formula(<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\text{MPTV}=2.5\Upsigma +0.7\delta\)</EquationSource> </InlineEquation>). The correlation between bladder filling status and setup errors in different directions was also analyzed. Results A total of 116 patients were included in the analysis, with 70 males and 46 females. The overall setup errors between males and females were as follows: in the left-right (LR) direction, (0.23 ± 1.82) mm vs. (−0.40 ± 1.95) mm (P < 0.001); in the superior-inferior (SI) direction, (−0.37 ± 3.01) mm vs. (0.65 ± 3.35) mm (P < 0.001); and in the anterior-posterior (AP) direction, (0.24 ± 1.83) mm vs. (0.16 ± 2.07) mm (P = 0.642). Significant differences in setup errors were observed in the coccyx region in all three directions (LR, SI, AP) and in the L5 region in the LR and SI directions. The PTV margins for males in the LR, SI, and AP directions were 3.9 mm, 5.0 mm, and 3.9 mm, respectively, while for females, they were 4.4 mm, 6.2 mm, and 4.6 mm, respectively. In the coccyx and L5 regions, the maximum PTV margin required for males was 6 mm in the SI direction, whereas for females, it was 7.4 mm in the SI direction. No correlation was found between bladder filling status and setup errors in any direction. Conclusion This study is the first to demonstrate that sex influences setup accuracy and PTV margins in rectal cancer patients undergoing VMAT radiotherapy. The overall registration errors underestimated the local regional errors. Bladder filling status did not correlate with setup errors. These findings provide important insights for personalized treatment planning.

The impact of sex on setup accuracy in radiotherapy for rectal cancer: a real-World observational study

期刊论文
发表日期：

2026年4月22日

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Fei Bai,
Tingting Hu,
Bo Li,
Jie Li,
Lihua Zhang,
Xiaowei Yao,
Fating Yang,
Hua Yang,
Linlin Xu,
Lina Zhao

摘要

Background/Purpose

Sex has been shown to influence the prognosis of various cancers. However, the impact of sex on setup accuracy in radiotherapy for rectal cancer has not been reported. To address this gap, we conducted a large-scale real-world study to analyze the influence of sex on setup accuracy and planning target volume (PTV) margins in rectal cancer patients undergoing radiotherapy.

Materials and Methods

We retrospectively collected data from rectal cancer patients treated with volumetric modulated arc therapy (VMAT) between January 2020 and December 2023. Patients were divided into male and female groups based on sex. Setup errors were compared between the two groups for the overall body, coccyx, and the fifth lumbar vertebra (L5) as regions of interest (ROIs). The PTV margins(With regard to setup errors alone)for each ROI were calculated using the van Herk formula( \(\text{MPTV}=2.5\Upsigma +0.7\delta\) ). The correlation between bladder filling status and setup errors in different directions was also analyzed.

Results

A total of 116 patients were included in the analysis, with 70 males and 46 females. The overall setup errors between males and females were as follows: in the left-right (LR) direction, (0.23 ± 1.82) mm vs. (−0.40 ± 1.95) mm (P < 0.001); in the superior-inferior (SI) direction, (−0.37 ± 3.01) mm vs. (0.65 ± 3.35) mm (P < 0.001); and in the anterior-posterior (AP) direction, (0.24 ± 1.83) mm vs. (0.16 ± 2.07) mm (P = 0.642). Significant differences in setup errors were observed in the coccyx region in all three directions (LR, SI, AP) and in the L5 region in the LR and SI directions. The PTV margins for males in the LR, SI, and AP directions were 3.9 mm, 5.0 mm, and 3.9 mm, respectively, while for females, they were 4.4 mm, 6.2 mm, and 4.6 mm, respectively. In the coccyx and L5 regions, the maximum PTV margin required for males was 6 mm in the SI direction, whereas for females, it was 7.4 mm in the SI direction. No correlation was found between bladder filling status and setup errors in any direction.

Conclusion

This study is the first to demonstrate that sex influences setup accuracy and PTV margins in rectal cancer patients undergoing VMAT radiotherapy. The overall registration errors underestimated the local regional errors. Bladder filling status did not correlate with setup errors. These findings provide important insights for personalized treatment planning.