直肠癌放疗不同技术和体位对小肠受照剂量的比较

目的:分析直肠癌放射治疗过程中，不同放疗技术和不同治疗体位对小肠受照射体积的影响。方法:选取18例直肠癌患者，膀胱充盈的状态下，治疗体位为仰卧位和俯卧位下分别扫描两组定位CT图像，分别传输至计划系统。在两组CT图像上分别制作三维适形（3D-CRT）和调强放射治疗（IMRT）计划，比较小肠在接受不同剂量的受照绝对体积差异（V5~45）。结果:相同体位，IMRT相比3D-CRT，小肠V45明显降低，V15两者基本接近。采用相同放疗技术，俯卧位相比仰卧位小肠V45和V15均明显降低。结论:直肠癌放射治疗，相比放疗技术，治疗体位对小肠受照体积的影响更大。

Influence of modern radiotherapy technique or treatment position on the irradiated volume in small bowel sparing for rectal cancer patients

Objective:To compare the effect of small bowel sparing between modern radiotherapy technique on intensity modulated radiotherapy(IMRT) and prone position with belly-board for rectal cancer radiotherapy.Methods:Eighteen rectal cancer patients underwent two series of CT scans,prone positioned with a belly board and supine positioned with a flat board,both combined using a full bladder protocol.Supine three dimensional conformal radiotherapy(3D-CRT),supine IMRT and prone 3D-CRT,prone IMRT plans were constructed for each patient.The volume of small bowel receiving doses in 5Gy increments from(5~45)Gy was calculated using dose-volume histograms for each plan.Results:Volumes of small bowel receiving dose in 5Gy increments from(5~45)Gy were calculated,from(35~45)Gy,there was a significantly lower volume of small bowel treated using the IMRT technique in both supine and prone positions.Compared with supine position,a trend was found for lower volume of irradiated small bowel at each dose level between 5 and 45Gy for prone position,whether using IMRT or not.The differences in small bowel V15 (the absolute volume of small bowel receiving at least 15Gy) and V45(the absolute volume of small bowel receiving at least 45Gy) between supine and prone position were significant.The V45 for the small bowel was significantly smaller for IMRT than 3D-CRT,but the V15 was approximately equal for IMRT and 3D-CRT.Conclusion:Patient position had a greater impact on small bowel sparing than modern radiotherapy technique.