鼻咽癌调强放疗中解剖结构改变对剂量分布影响研究

Impact of anatomical changes on dose distribution of intensity-modulated radiotherapy for nasopharyngeal carcinoma

目的 利用变形融合与配准技术观察和分析鼻咽癌调强放疗（IMRT）过程中患者体形和几何结构改变及对治疗剂量分布的影响.方法 随机选取实际接受IMRT的鼻咽癌患者10例,利用疗程中重复CT图像,根据初始计划轮廓和变形融合配准软件自动勾画疗程中鼻咽和转移淋巴结大体肿瘤体积（GTVnx、GTVnd）、临床靶体积和危及器官（OAR）.分别计算和评估GTVnx、GTVnd 、 OAR体积改变和变化规律,以及剂量参数相对原计划的改变.结果 与治疗前相比,治疗2、4、6周时GTVnx体积分别缩小6.44%、10.23%、9.72%（F=1.34,P=0.278）,GTVnd的分别缩小16.59%、30.98%、35.13%（F=9.22,P=0.000）,CTV1的分别缩小0.73%、1.86%、1.41%（F=0.33,P=0.722）,CTV2的分别缩小-1.78%、-6.47%、-9.34%（F=16.89,P=0.000）,左腮腺的分别缩小13.96%、32.97%、37.77%（F=17.17,P=0.000）,右腮腺的分别缩小13.56%、29.57%、35.63%（F=13.49,P=0.000）.与计划的分次剂量相比,治疗2、4、6周时GTVnx平均剂量变化率分别为-0.39%、0.08%、0.32%（F=0.15,P=0.860）,GTVnd的分别为0.53%、1.19%、0.69%（F=0.81,P=0.455）,脊髓的分别为1.95%、2.70%、3.78%（F=0.61,P=0.552）,脑干的分别为0.32%、0.81%、0.62%（F=0.03,P=0.975）,左腮腺的分别为4.50%、4.66%、7.20%（F=0.33,P=0.725）,右腮腺的分别为2.20%、7.17%、7.12%（F=1.24,P=0.306）.结论 鼻咽癌IMRT时GTVnd、CTV2和左右腮腺体积随治疗时间增加明显退缩,而GTV、CTV、脊髓、脑干、腮腺分次剂量随治疗时间增加变化不大,但最终还须加大样本量研究证实.

Objective To observe the physique and anatomy changes in patients with nasopharyngeal carcinoma （NPC） during intensity-modulated radiotherapy （IMRT）, using repeated CT images and deformable registration technique, and analyze their impact on delivery dose distribution.Methods Ten NPC patients were randomly selected from those who had received IMRT treatment.Gross tumor volume of nasopharyn （GTVnx）, GTV of metastastatic lymph node （GTVnd）, clinical target volume （CTV） and normal tissue or organ （OAR） were re-contoured on the in-course repeated CT images using a kind of deformable registration and auto-segmentation software according to the original planning contouring.Changes in volume of treatment targets and organs at risk were evaluated and the trends were then analyzed.Dose distributions were recalculated with repeated CT images and compared to the original plans.Results The volume of GTVnx were decreased by 6.44%,10.23% and9.72%（F=1.34,P=0.278） in the 2-,4-and 6-week after IM RT comparing with before IM RT, with 6.59%, 30.98 % and 35.13 % （F = 9.22, P =0.000） in GTVnd, 0.73%, 1.86% and 1.41% （F=0.33,P=0.722） in CTV1, -1.78%, -6.47%and -9.34% （F =16.89 ,P =0.000） in CTV2, 13.96%, 32.97% and 37.77%（F=17.17,P=0.000）in the left parotid , and 3.56% , 29.57% and 35.63% （F = 13.49 , P = 0.000） in the right parotid.The mean dose change rate of GTVnx were -0.39%, 0.08% and 0.32% （F =0.15 ,P =0.860） in the 2-,4- and 6-week after IMRT comparing with planning faction dose, with 0.53%, 1.19% and 0.69% （F=0.81,P=0.455） in GTVnd, 1.95%, 2.70% and 3.78% （F=0.61,P=0.552） in the spinal cord,0.32%, 0.81% and 0.62% （F=0.03,P=0.975） in the brain stem, 4.50%, 4.66% and 7.20% （F=0.33,P=0.725） in the left parotid, 2.20%, 7.17% and 7.12% （F= 1.24,P=0.306） in the right parotid.Conclusions The GTVnd, CTV2 and parotids shrinks obviously along with the treatment times for NPC patients during IMRT.Although changes in fraction dose of GTV, CTV, spinal cord, stem and parotids are not significant, further study with larger samples is needed.