鼻咽癌调强放疗中靶区剂量变化规律研究

目的 研究鼻咽癌调强放疗(IMRT)过程中肿瘤靶区变化对剂量分布的影响.方法 21例行根治性IMRT初程治疗鼻咽癌患者分别于计划设计前及治疗开始后前5周每周固定同一天行螺旋CT扫描各1次,共126次.以计划制定前扫描cT的3个体表标记点作为参考标记并确定靶区中心,然后由计划系统进行正向计算,得出治疗开始后前5周每周CT扫描时的靶区实际受量,比较其间有无差异并与计划设计前相比较.结果 GTV_(nx) CTV_1、CTV_2在治疗过程中连续5周每周同时间采集的D_(mean)、D_(95)、D_(90)、D_(10)、D_5和V_(100)经方差分析均相似,GTV_(nx)的分别为15.44～15.60 Gy(F=0.07,P=0.996)、14.66～14.92 Gy(F=0.11,P=0.990)、14.81～15.06 Gy(F=0.12,P=0.988)、15.88～16.29 Gy(F=0.28,P=0.924)、16.00～16.38 Gy(F=0.25,P=0.940)、98.1%～99.5%(F=0.08,P=0.995),CTV_1的分别为14.75～14.98 Gy(F=0.07,P=0.997)、13.39～13.73 Gy(F=0.20.P=0.964)、13.74～13.96 Gy(F=0.08,P=0.995)、15.65～15.90 Gy(F=0.09,P=0.994)、15.91～16.05 Gy(F=0.10,P=O.992)、98.2%～99.5%(F=0.02,P=1.000),CTV_2的分别为13.34～13.64 Gy(F=0.18,P=0.970)、12.71～13.18 Gy(F=0.32,P=0.898)、12.89～13.28 Gy(F=0.23,P=0.949)、13.79～14.03 Gy(F=0.12,P=0.987)、13.92-14.16 Gy(F=0.12,P=0.987)、94.4%～99.6%(F=0.25,P=0.937).结论 鼻咽癌调强放疗中随靶区变化其剂量变化不显著,即使在外轮廓变化最大点处初始计划仍能很好地覆盖靶区,因此临床上因肿瘤靶区改变而修订计划的意义不大.

Dose distribution variation of target volumes in nasopharyngeal carcinoma treated with intensity modulated radiotherapy

Objective To analyze the dose distributions of changing target volumes during intensity modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC). Methods Twenty-one NPC patients received definitive IMRT. A total of 126 computed tomography (CT) planning images were acquired, including the first CT scan for the primary plan and a series of scans taken weekly from the start of treatment to the fifth week. The images were registered to the planning images. Target volumes (GTV_(nx), CTV_1 ,CTV_2 ,PTV, and PTV_2) and normal structures (the parotid, brain stem and spinal cord) were re-contoured on the fusion CT images. Results The D_(mean) D_(95), D_(90), D_(10), D_5 and V_(100) of GTV_(nx) were 15.44 -15.60 Gy (F=0.07,P=0.996),14.66 -14.92 Gy (F=0. 11,P=0.990),14.81 -15.06 Gy (F= 0. 12,P=0.988),15.88 -16.29 Gy (F =0.28,P=0.924),16.00 -16.38 Gy (F=0.25,P =0. 940) and 98. 1% -99. 5 % (F = 0. 08, P = 0. 995), CTV_1 with 14. 75 -14. 98 Gy (F = 0. 07,P = 0. 997), 13.39 -13.73 Gy (F=0.20,P=0.964),13.74 -13.96 Gy (F=0.08,P=0.995), 15.65 -15.90 Gy (F= 0.09,P=0.994),15.91 -16.05 Gy (F=0. 10,P=0.992), 98.2% -99.5% (F=0.02,P= 1.000), and CTV_2 with 13.34 -13.64 Gy (F=0. 18,P=0.970),12.71 -13. 18 Gy (F=0.32,P=0.898), 12.89 -13.28Gy(F=0.23,P=0. 949) ,13.79 -14.03Gy(F=0. 12,P=0. 987) ,13.92 -14. 16 Gy (F=0. 12,P=0.987), 94.4% -99.6% (F=0.25,P=0.937), respectively. Conclusions No significantly different dose distributions exists with the changes of the target volumes, even on the largest variations of external contours. The primary plan could ensure adequate doses to the changing target volumes. The replanning is unnecessary in terms of the change of target volumes during radiotherapy.