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目的调强放射治疗(IMRT)能较好的保护危及器官并给予肿瘤足够的致死剂量,基于多叶准直器(MLC)分步照射的IMRT技术对复杂病例需要更多子野。研究对直肠癌术后放射治疗使用不同子野数目的IMRT计划进行比对,选择合理的子野数。方法选取2010年48月入院的直肠癌术后患者10例,保持射野入射角度及优化目标参数相同,仅改变MLC子野数目,设计不同IMRT对每一患者治疗计划的靶区适形指数(CI)、均匀性指数、最大剂量、最小剂量、平均剂量,危及器官关注体积的受照剂量,机器跳数及治疗时间进行分析。结果所有治疗计划中靶区及危及器官的剂量学评估指标无统计学意义(P>0.05),只有亚临床计划靶区(PTV)CI在15个子野的方案中(0.74±0.06)明显差于25个子野方案(0.82±0.03)、40个子野方案(0.81±0.06)及60个子野方案(0.84±0.03),有统计学意义(P<0.05);治疗机器跳数(MU)随子野数目增多明显增大,15、20、40及60个子野方案所需MU分别为(458±56)、(559±62)、(614±74)、(622±82),有统计学意义(P<0.05),但40个子野方案与60个子野方案间无统计学意义。治疗时间明显随子野数增加而增大。结论直肠癌术后IMRT计划使用25个子野能满足临床剂量要求,同时能有效降低治疗时间,可作为临床应用参考值。
Objective IMRT can protect the endangered organs and give enough lethal dose to the tumor. IMRT based on multi-leaf collimator (MLC) step-by-step irradiation requires more subfields for complex cases. To compare the number of IMRT plans using different number of subfields for postoperative radiotherapy of rectal cancer, and to select a reasonable number of subfields. Methods Ten patients with postoperative rectal cancer admitted in hospital in 2010 were selected. The incidence angle and the optimal target parameters were kept the same. Only the number of MLC subfields was changed. The conformal index of the target area for each patient’s treatment plan was designed. CI), Uniformity Index, Maximum Dose, Minimum Dose, Average Dose, Exposed dose that endangers the volume of organ of concern, Machine hop count, and Treatment time are analyzed. Results There were no statistically significant differences in the dosimetry of the target area and the endangered organs in all treatment plans (P>0.05). Only subclinical plan target (PTV) CI was significantly worse in the 15 subfields (0.74±0.06). Twenty-five subfield protocols (0.82±0.03), 40 subfield protocols (0.81±0.06) and 60 subfield protocols (0.84±0.03) were statistically significant (P<0.05); the number of hops (MU) of treatment machines varied with subfields The number increased significantly. The MUs required for 15, 20, 40, and 60 subfield programs were (458±56), (559±62), (614±74), (622±82), respectively, which was statistically significant ( P<0.05), but there was no statistical difference between the 40 subfields and the 60 subfields. Treatment time increased significantly with increasing number of subfields. Conclusion IMRT plans to use 25 subfields for rectal cancer surgery to meet the clinical dose requirements, and can effectively reduce the treatment time, which can be used as a reference value for clinical application.