直肠癌五野调强放疗与传统适形放疗剂量学研究

Dosimetric study of five-field intensity modulated radiotherapy compared with conventional three-dimensional conformal radiotherapy for rectal cancer

目的:研究五野调强技术(IMRT)与三维适形(3DCRT)技术治疗直肠癌肿瘤靶区和危及器官照射剂量的区别。方法:回顾性分析15例直肠癌患者的放疗资料,其中7例为术前放疗,8例为术后放疗。在每位患者的模拟定位CT上分别勾画肿瘤靶区及小肠、膀胱、股骨头等危及器官(OAR),并分别进行3DCRT和IMRT计划设计,要求处方剂量至少覆盖95%的计划靶体积。应用适形指数(CI)和均匀指数(HI)评价肿瘤靶区剂量的分布,应用Dx%(接受高量照射的x%的体积所受到的最低剂量)和平均剂量评价OAR受照射剂量。两个计划剂量分布的差别采用配对t检验比较。结果:在IMRT和3DCRT计划中,CI分别为0.94和0.87(P=0.000);HI分别为1.13和1.17(P=0.001);小肠D30%分别为19.67Gy和25.20Gy,D50%分别为15.13Gy和22.20Gy,平均剂量分别为18.81Gy和22.89Gy(P均为0.000);膀胱的D30%分别为34.20Gy和44.67Gy,D50%分别为24.80Gy和35.07Gy,平均剂量分别为28.70Gy和35.68Gy(P均为0.000);股骨头D5%分别为40.60Gy和40.47Gy(P=0.936),平均剂量分别为30.14Gy和25.57Gy(P=0.001)。结论:IMRT在靶区剂量均匀性和适形度方面均优于3DCRT计划,对正常组织的保护也存在明显的优势。

Objective：To compare the difference of dose distribution in clinical target volume and organ at risk （OAR） between five-field intensity modulated radiotherapy （IMRT） and conventional three-dimensional conformal radiotherapy （3DCRT） in the radiotherapy of rectal cancer. Methods：Fifteen patients with rectal cancer treated with radiotherapy （RT） were retrospectively analyzed. Among the patients, seven received RT preoperatively and 8 postoperatively. The target volume and the organ at risk such as the small intestine, bladder and femoral head were contoured for each patient. 3DCRT plan and IMRT plan were performed for each patient respectively, with the prescribed dose covering at least 95% of the planning target volume （PTV）. The conformity index （CI） and homogeneity index （HI） were used for evaluation of the dose distribution in the tumor target volume, and the Dx% （the lowest dose to the x% volume of the OARs that received the highest dose of irradiation） and the mean dose were used for evaluation of the dose to OARs. Paired-T test was used for comparison of the difference between the two plans. Results： In the IMRT-plan and 3DCRT-plan, the CI were 0. 94 and 0. 87 （P =0. 000） and the HI werel. 13 and 1.17, respectively （P =0. 001 ）. For small intestine, the D30%, D50% and the mean dose were 19. 67Gy, 15. 13Gy and 18.81Gy in the IMRT-plan and were 25.20Gy, 22. 20 Gy and 22. 89Gy in the 3DCRT-plan, respectively （ P 〈 0. 001 for all pairs of parameters）. For bladder, the D30%, D50%, and the mean dose were 24. 80Gy, 34. 20Gy and 28. 70Gy in the IMRT-plan, and 35.07Gy, 44. 67Gy and 35.68Gy in the 3DCRT-plan, respectively （P 〈 0. 001 for all pairs of parameters）. For femoral head, the D5% in the IMRT-plan and 3DCRT-plan were 40. 6Gy and 40.47Gy, respectively （ P = 0. 936 ）, and the mean dose were 30. 14Gy and 25.57Gy, respectively （ P = 0. 001 ）. Conclusion ： IMRT plan is better than 3DCRT plan in conformity and dose homogeneity within target volume and also better in sparing the small intestine and bladder.