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目的比较直肠癌术前同期加量放疗中容积旋转调强放疗(volumetric modulated arc therapy,VMAT)和螺旋断层放疗(helical tomotherapy,HT)计划的剂量学差异。方法对10例Ⅱ~Ⅲ期直肠癌术前同步放化疗患者分别进行VMAT和HT的计划设计,统一给予肿瘤原发病灶及转移淋巴结(肿瘤大体靶区,pGTV)处方剂量56.25 Gy/25 F,高危复发区域和区域淋巴引流区(计划靶区,PTV)50 Gy/25 F,利用剂量体积直方图评价靶区剂量分布和危及器官照射剂量。结果与HT计划相比,VMAT计划的pGTV适形指数(conformity index,CI)CIpGTV变差(t=-2.803,P=0.005),PTV的中位剂量和最小剂量(D98)升高(t=8.895、3.663,P=0.000、0.005)。对小肠的保护VMAT计划优于HT计划,VMAT计划的小肠V15比HT计划降低约19%(t=-3.802,P=0.004)。VMAT计划骨盆V10低于HT计划(t=-7.047,P=0.000),但骨盆V30高于HT计划(t=4.704,P=0.001)。对膀胱的保护HT计划略优于VMAT计划。VMAT计划机器跳数比HT计划降低约89%(t=-2.666,P=0.008)。结论直肠癌术前同期加量放疗中采用VMAT技术可获得与HT计划相当的剂量分布,对小肠保护略有优势,机器跳数明显降低,但其疗效还需进一步临床评估。
Objective To compare the dosimetry differences between volumetric modulated arc therapy (VMAT) and helical tomotherapy (HT) in rectal cancer preoperatively. Methods The planned design of VMAT and HT were performed in 10 patients with stage Ⅱ ~ Ⅲ rectal cancer before operation. The prescribed dose of 56.25 Gy / 25 F was given uniformly to primary tumor and metastatic lymph nodes (pGTV) High-risk recurrence and regional lymphatic drainage (planned target area, PTV) 50 Gy / 25 F, dose-volume histogram to assess the target dose distribution and endanger the dose of organ irradiation. Results The pGTV conformal index (CI) CIpGTV of the VMAT plan was significantly lower than that of the HT plan (t = -2.803, P = 0.005), and the median and minimum dose of PTV (D98) 8.895, 3.663, P = 0.000, 0.005). The protection of the small intestine was superior to the HT plan for the VMAT program, which reduced the V15 of the small intestine by about 19% from the HT plan (t = -3.802, P = 0.004). VAT was lower in the VMAT than in the HT (t = -7.047, P = 0.000), but pelvic V30 was higher than in the HT (t = 4.704, P = 0.001). The Bladder Protection HT program is slightly better than the VMAT program. The VMAT plan machine hop count was approximately 89% lower than the HT plan (t = -2.666, P = 0.008). Conclusions The dose distribution of HTAT with VMAT can be obtained in the preoperative radiotherapy of rectal cancer. It has a slight advantage in the protection of small intestine and a significant decrease in the number of hops. However, its efficacy needs further clinical evaluation.