鼻咽癌调强放疗中目标剂量覆盖率的研究

To Dissect the Subject about Dose Coverage in the Design of Intensity Modulated Radiation Therapy Plan for Nasopharyngeal Carcinoma

目的:探索鼻咽癌调强放疗计划中目标剂量是否最大限度覆盖靶区,是否同时满足靶区和重要器官的处方剂量和目标耐受量要求。方法:随机选取70例鼻咽癌病人的PTV70、PTV66、PTV60和PTV50.4作为研究对象,用剂量体积直方图有关参数进行分析,来评价靶区剂量覆盖率、适形度和不均匀性指数等,并分析正常组织耐受量的余量问题。结果:在四个靶区中,大于85%以上的等剂量面覆盖PTV70和PTV66为100%,其中满足大于93%处方剂量的覆盖率分别为80%和84%;PTV60和PTV50.4覆盖率不理想,大于85%以上的等剂量面覆盖率为75%和50%,其中满足大于93%处方剂量的覆盖率只有44%和39%,所有靶区的最大剂量均小于110%的处方剂量。正常组织中脊髓、脑干、视交叉、视神经1%体积所受最大剂量均值为39 Gy、51 Gy、45 Gy和42 Gy,和目标耐受量相比还有22%、15%、25%和30%的余量;晶体、眼球全部体积所受平均剂量均值为2 Gy和7 Gy,和目标耐受量相比,还有50%和80%的余量。腮腺受量只有16%的病人健侧50%体积所受剂量小于26 Gy以下,其余全部体积的平均剂量均值为36 Gy,无加量余地。结论:本研究显示各正常器官除腮腺外还有15%-30%的余量,如果按鼻咽癌的剂量响应梯度19%即再增加靶区19%的处方剂量(GTV总量达83Gy),是可以用正常组织的耐受余量来完成的,那么将鼻咽癌的局部控制率再提高20%应是可行的。在同期整合推量照射(simultaneous integrated boost,SIB)技术中,PTV70和PTV66能得到确定的剂量,但是要注意PTV60和PTV50.4的低剂量区。

Objective： To explore the coverage of the target dose in the process of IMRT in the treatment of nasopharyngeal carcinoma,and the satisfaction degree of the target doses for both target volume and critical normal tissues. Methods： To evaluate coverage rate of target doses, conformity index （CI）, homogeneity index （HI）, and to analyze the coverage of the objective tolerance doses in normal tissues by using dose-volume histogram （DVH） in 70 randomized selected NPC patients whose PTVT0, PTV~, PTV~,, and PTVs（~4 were studied. Results： In four targets, for the PTVT0 and PTV6~, the coverage rate of the isodose curve of 85% and above are all 100%, and of 93% and above, is 80% and 84%, respectively. For the PTV6o and PTV594 the coverage rate of the isodose curve of 85% and above is 75% and 50%, respectively, and of 93% and above, is only 44% and 39%, respectively. Maximum doses in all target volumes are less than 110% of the described dose. Among the critical normal tissues, received mean value of maximum dose in 1% volume of spinal cord, brain stem, chiasm and optic nerve are 39 Gy,51 Gy,45 Gy and 42 Gy, respectively. Comparing with their objective tolerance doses, the remaining tolerance doses are 22%,15%,25% and 30%,respectively. The mean received doses in whole volume of lens and eyes are 2 Gy and 7 Gy. Comparing with their objective tolerance doses,the remaining doses are 50% and 80%,respectively. For parotid,it is difficult to restrict tolerance dose,only 16 % of single parotid meet tolerance doses which are less than 26 Gy, and others＇ volume mean tolerance doses are 36 Gy. Conclusion： All critical normal structures except parotid have 15%-30% of remaining tolerance dose. NPC has a dose response gradient of 19%, with IMRT, the prescribed dose of target volume can be increased by 19% （up to 83 Gy） though using remaining tolerance doses. In this way, it is hopeful to elevate the local control rate of 20% for nasopharyngeal carcinoma. With（simultaneous integrated boost, SIB） technique, PTV70 and PTV66 can achieve an assured dose, more attention must be paid to low dose areas in the PTV60 and PTV504.