Objective To explore the radio therapeutic positioning errors and radiation dose distribution between different kinds of fixation modes and BMI of patients in carcinoma of the rectum. Methods 96 patients with rectal cancer who underwent radiotherapy were selected from March 2014 to June 2016,each patient's BMI was calculated. According to the method of random numbers they were divided into A,B two groups,each group of 48 cases. Group A were treated by "traditional supine small vacuum pad fixed method",group B were treated by "body prone thermoplastic film + perforated web fixed method". Both of two groups of cases were conducted three stages before radiotherapy by CT simulation location,3D image reconstruction,the outline of the target area and endanger the normal organs. Treatment plan was adopted IMRT 5-7 days,and the volumes of the small bowel, bladder and femoral head were calculated on a dose volume histogram of two groups. During the treatment, images obtained from the CBCT scan before radiotherapy were registered with the scanned images of the CT simulator produced by the TPS planning system. The different BMI range, different ways of fixed hem error and irradiated dose difference were compared. Results Compared with normal group,lanky group was relatively close,overweight group and obese group had difference,which the error was the most obvious in obesity group,the left and right were the most significant. On the small intestine by the exposure dose for normal group and lean group,overweight and obese increased significantly(t=1.59,P<0.05). Around A group of patients before and after and the direction of the beam position error were significantly higher than that of group B,the difference was statistically significant (t=2.88,P<0.05,t=2.37,P<0.05),two groups of patients with head foot placement direction error had no statistical significance (t=1.47,P>0.05).Two groups of patients with femoral head there was no statistically significant difference by quantity (t=0.41,P>0.05);A group of patients with small intestine dose (24.76±1.64) was significantly higher than group B (13.33±2.12) (t=2.81,P<0.05);A group of patients with bladder volume (24.91±2.12) lower than that of group B (25.71±2.67),but there was no statistically significant difference (t=0.92,P>0.05). Conclusion Colorectal cancer patients with BMI and different fixed way affect the positioning error and radiation dose.%目的 探讨直肠癌患者BMI及不同固定方式对放疗摆位误差、剂量分布的影响.方法 选取2014年3月至2016年6月行放射治疗的直肠癌患者96例,入院治疗时计算每例患者BMI指数.依照随机数字法分为2组,每组各48例.A组患者采取仰卧位"真空垫固定法",B组患者采取俯卧位"热塑体膜+有孔腹板固定法".两组患者均经过放疗前CT模拟定位-3D图像重建-靶区与正常危及器官的勾画等三阶段,采用5～7d调强放射治疗计划,在剂量-体积直方图上计算两组小肠、膀胱和股骨头的受量.治疗期间,在放射治疗前行CBCT扫描所得图像,与TPS计划系统输出的CT模拟机扫描所得图像进行配准摆位误差.比较不同BMI区间、不同固定方式下摆位误差和受照射剂量的差异.结果 摆位误差:与正常组比较,体瘦组较为接近,超重组和肥胖组误差增大,其中肥胖组误差最明显,又以左右方向最显著.小肠受照射剂量上亦为正常组和较瘦组接近,而超重组与肥胖组显著增加(t=1.59,P<0.05).A组患者左右与前后方向的摆位误差均较B组显著增高,差异有统计学意义(t=2.88,P<0.05;t=2.37,P<0.05),两组患者头脚方向摆位误差无统计学意义(t=1.47,P>0.05).两组患者股骨头受量差异无统计学意义(t=0.41,P>0.05);A组患者小肠剂量(24.76±1.64)明显高于B组(13.33±2.12)(t=2.81,P<0.05).结论 直肠癌患者的BMI指数和不同固定方式对放疗时的摆位误差和受照剂量均有较大影响.
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