F. Bai1, L. L. Xu2, and L. N. Zhao3; 1Department of Radiation Oncology, Xijing Hospital, Fourth Military Medical University, xian, Shaanxi, China, 2Department of Radiation Oncology, Xijing Hospital, Fourth Military Medical University, xian, shaanxi, China, 3Department of Radiation Oncology, Xijing Hospital, Air Force Medical University, Xian, China
Purpose/Objective(s): Gender is increasingly recognized as an important factor in medicine, although it has long been neglected in medical research in many areas. The influence of gender on setup accuracy in rectal cancer radiotherapy has not been reported. To fill this gap on the effect of gender on setup accuracy in rectal cancer radiotherapy, we conducted a large real-world study. Our aim was to analyze the effect of gender on setup accuracy and PTV margins in patients undergoing radiotherapy for rectal cancer. Materials/
Methods: Between January 2020 and August 2023, we retrospectively collected VMAT radiotherapy patients diagnosed with rectal cancer. They were divided into male and female groups according to gender. The overall setup errors (the overall registration frame covering the entire pelvic region) and setup errors using the coccyx and fifth lumbar vertebrae as regions of interest were compared between the two groups of patients. The PTV margins for each region of interest were calculated according to the formula of van et al.MPTV =2.5S+0.7d. The correlation between the different degrees of bladder filling and the setup errors in each direction was analyzed. Results: A total of 569 CBCT data from 116 patients were available for analysis, 70 males (median age 57 years, range 27-84 years) and 46 females (median age 57 years, range 27-82 years). Total setup error of males vs. females, ML direction: (0.23±1.82) vs (-0.40±1.948) mm (P<0.001). SI direction: (-0.37±3.01) vs (0.65±3.35) mm (P<0.001). AP direction: (0.25±1.81) vs (0.16±2.07) mm (P=0.594). Setup errors in the coccyx region, ML direction: (0.20±1.78) vs (-0.33±1.97) mm (P=0.001 ). SI direction: (-0.61±3.36) vs (0.73±3.96) mm (P<0.001). AP direction: (0.33±2.09) vs (-0.18±2.38) mm (P=0.008). Setup errors in the L5 region, ML direction: (0.47±1.76) vs (-0.29±1.99) mm (P<0.001 ). SI direction: (0.24±3.34) vs (1.50±3.78) mm (P<0.001). AP direction: (0.20±2.74) vs (0.11±2.52) mm (P=0.708). The total PTV margins in the ML, SI and AP directions were 3.9 mm, 5.0 mm and 3.9 mm in males and 4.4 mm, 6.2 mm and 4.6 mm in females; in the coccyx region the margins were 3.6 mm, 5.7 mm and 4. 7 mm in males and 4.4 mm, 7.4 mm and 5.5 mm in females; in the L5 region, 3.6 mm, 5.8 mm and 5.8 mm were required in males and 4.3 mm, 7.0 mm and 5.0 mm in females. There was no correlation between different levels of bladder filling and setup errors in all directions. Conclusion: This study demonstrates for the first time that setup accuracy and PTV margin differ by gender in VMAT radiotherapy for rectal cancer. Setup errors were smaller in males than in females. Males require a maximum PTV margin of 5 mm in the SI direction, whereas females require a margin of 6 mm. These findings provide important evidence for individualized PTV margins.
