Research on CTV referential safety margins modification of PTV study in 247 cases of Three-dimensional Conformal Radiotherapy target volume
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摘要:
目的研究肿瘤三维适形放疗临床靶区到计划靶区外扩边界的范围。 方法对2013年1月~12月间我科应用三维适形放疗的247例患者进行复位前后和第N（N为随机量）次治疗前后选取固定正、侧位野拍摄等距离验证片各1张，运用HW-TPSQA软件与计划系统中的照射野数字重建影像进行比较，得出摆位误差。每例患者各个方向的摆位系统误差以Σ表示，摆位随机误差以σ表示，放疗靶区CTV到PTV外扩边界的范围以SCTV→PTV表示，依据Van Herk等推导公式SCTV→PTV=2.5Σ+0.7σ。 结果肿瘤三维适形放疗靶区CTV外扩PTV边界范围的参考数据：头颈部x、y、z方向外扩边界参数分别为1.09、0.62、2.42 mm；胸、上腹部x、y、z方向外扩边界参数分别为2.36、4.04、3.69 mm；下腹部x、y、z方向外扩边界参数分别为2.79、2.23、3.11 mm。 结论本研究为肿瘤三维适形放射治疗CTV外扩PTV边界范围的确定和修正提供有效的理论依据，降低肿瘤靶区遗漏的可能性，使得肿瘤三维精确适形放射治疗的优越性得到充分的发挥。 Abstract:Objective Tostudy the reference data of CTV referential safety margins of PTV in Three-dimensional Conformal Radiotherapy target volume. Methods The translational deviation of 247 patients during Jan~Dec. in 2013 were examined in this study. Thermoplastic mask was used for head and neck and vacuum cushion was used for chest and abdomen immobilization. The verification films were taken for each patient prior the first treatment and the Nth were compared with the digitally reconstructed radiographs (DRR) by the HW-TPSQA system, in order to make translational deviation. CTV margin should be calculated with the formula 2.5Σ+0.7σ by Van Herk al. Σ means Systematic Error, σ means Random Error. Result The margin of PTV of head and neck in three directions (X, Y, Z) was 1.09 mm, 0.62 mm, 2.42 mm respectively, the margin of PTV of chest in three directions (X,Y, Z) was 2.36 mm,4.04 mm,3.69 mm and the margin of PTV of abdomen in three directions (X, Y, Z) was 2.79 mm, 2.23 mm, 3.11 mm. Conclusion It has laid a theoretic foundation for our CTV margins by analyzing the translational deviation and made our design of radiotherapy system more scientific and normal in Three-dimensional Conformal Radiotherapy target volume. -
表 1 头颈部摆位误差相关结果及外扩边界
Table 1. The related factors of translational deviation and margin in three directions of head-neck tumors (mm)
方向 病例数 均值 标准差 摆位误差 中位数 误差极值 MPTV Σ σ Max Min X 58 -0.1143 2.4748 -0.14 0.98 -1.3 2.7 -2.1 1.09 Y 58 0.2657 3.0729 0.04 0l.62 0.2 3.1 -2.7 0.62 Z 58 0.0148 4.6231 -0.64 0.96 0.3 4.9 -2.6 2.42 X正负、值分别为左、右方向; Y正负、值分别为头、脚方向; Z正负、值分别为腹、背方向. 
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表 2 胸部摆位误差相关结果及外扩边界
Table 2. The related factors of translational deviation and margin in three directions of chest tumors (mm)
方向 病例数 均值 标准差 摆位误差 中位数 误差极值 MPTV Σ σ Max Min X 87 -0.4258 2.5863 -0.18 2.97 -0.8 5.6 -7.9 2.36 Y 87 0.8762 5.4769 0.94 2.33 0.7 9.9 -9.7 4.04 Z 87 0.1026 3.3189 0.57 2.81 -0.2 6.2 -9.6 3.69 X正负、值分别为左、右方向; Y正负、值分别为头、脚方向; Z正负、值分别为腹、背方向.
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表 3 腹部摆位误差相关结果及外扩边界
Table 3. The related factors of translational deviation and margin in three directions of abdomen tumors (mm)
方向 病例数 均值 标准差 摆位误差 中位数 误差极值 MPTV Σ σ Max Min X 102 -0.2972 3.2748 0.57 1.79 -2.3 8.7 -7.6 2.79 Y 102 0.3871 6.5729 0.07 2.54 0.1 9.8 -8.9 2.23 Z 102 0.1727 4.2231 0.62 2.37 0.4 9.6 -10.2 3.11 X正负、值分别为左、右方向; Y正负、值分别为头、脚方向; Z正负、值分别为腹、背方向.
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表 4 胸部摆位误差范围及剂量分布
Table 4. The percent of set-up errors and the different dose distribution in three directions of chest tumors (mm)
摆位误差 X方向 Y方向 Z方向 ≤ 5 mm 93.44% 85.25% 91.80% 5~10 mm 6.56% 14.75% 8.20% >10 mm 0% 0% 0% 90%剂量分布 -4.7~3.8 -8.2~8.9 -5.4~5.6 95%剂量分布 -5.5~4.6 -9.9~9.8 -6.4~6.6
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表 5 腹部摆位误差范围及剂量分布
Table 5. The percent of set-up errors and the different dose distribution in three directions of abdomen tumors (mm)
摆位误差 X方向 Y方向 Z方向 ≤ 5 mm 89.00% 80.59% 80.10% 5~10 mm 11.00% 19.40% 17.91% >10 mm 0% 0% 2% 90%剂量分布 -4.7~3.8 -8.2~8.9 -5.4~5.6 95%剂量分布 -5.5~4.6 -9.9~9.8 -6.4~6.6
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