静态调强放疗等中心点对鼻咽癌剂量学的影响

Dosimetric effects of isocenter on static intensity-modulated radiotherapy for nasopharyngeal carcinoma

目的:分析调强放射治疗等中心点的选择对鼻咽癌剂量学的影响,为治疗计划的设计提供参考依据。方法:选取17例鼻咽癌病例,分别以原发肿瘤和咽后淋巴结临床治疗靶区PGTVnx的中心点(以AP表示)和预防照射区临床治疗靶区PTV的中心点(以BP表示)作为治疗计划的等中心点,设计调强放疗计划。比较靶区的适形度指数以及均匀性指数、危及器官的最高剂量以及正常组织的低剂量体积。结果:两种治疗计划均能满足临床剂量要求。在所有靶区剂量体积百分比没有明显统计学差异情况下,AP组和BP组的靶区的适形度指数以及均匀性指数差异无统计学意义。但是AP组的视交叉_(D0.03 cm^3)剂量要明显低于BP组,分别为(36.7±12.1)Gy和(38.8±11.2)Gy(t=-3.070, P<0.01);AP组的正常组织V<30 Gy明显大于BP组,分别为(8 250±1 686)cm3和(8 166±1 669)cm^3(t=3.799, P<0.01)。结论:AP能明显降低视交叉的最高剂量,并且能降低正常组织的高剂量体积,减少病人的正常组织放疗并发症概率。

Objective To analyze the dosimetric effects of different isocenters on intensity-modulated radiotherapy(IMRT) for nasopharyngeal carcinoma(NPC) for providing reference for the design of treatment plan. Methods Seventeen patients with NPC were enrolled in this study. Two different kinds of IMRT plans were designed with different isocenters, namely one with the center of the primary tumor and pharyngeal lymph nodes clinical target area PGTVnx(AP) and the other with the center of prophylactic irradiation area clinical target area PTV(BP). The conformity index and homogeneity index of target areas, the maximum dose of organs-at-risk, and the low dose volume of normal tissues were compared between two different plans. Results Both two different kinds of IMRT plans met clinic dosimetric requirements. In the case of no statistical differences were found in the dose volume percentage of target areas, the homogeneity index and conformity index of target areas were similar in AP group and BP group, but compared with BP group, AP group had lower D0.03 cm3 of the optic chiasm [(36.7±12.1) Gy vs(38.8±11.2) Gy;t=-3.070,P<0.01] and higher V<30 Gyof normal tissues [(8 250±1 686) cm3 vs(8 166±1 669) cm3;t=3.799, P<0.01]. Conclusion AP can significantly decrease the maximum dose of optic chiasm and the high dose volume of normal tissues, so as to lower the normal tissue complication probability.