鼻咽癌调强放疗根据CT和MRI勾画腮腺的比较研究

摘要

Objective To compare the differences of volume and DVH between the CT-defined and the MRI-defined parotids for intensity modulation radiated therapy (IMRT) planning on 20 patients with nasopharyngeal carcinoma (NPC).Methods Twenty patients diagnosed NPC from May 2008 to November 2008 were enrolled in this study.They received MRI and CT scan one week before radiotherapy and the images were transmitted to the treatment planning system,where the volume of parotid based on CT or MRI were contoured respectively.After fusing the CT/MRI image by using mutual information method,the difference of the volume between CT-defined and the MRI-defined parotid was evaluated.The IMRT plan was based on CT image,then the difference of DVH between CT-defined and MRI-defined parotid was compared.Results The mean volumes of parotid contoured on CT and on MRI were (24.53±1.96×7.23)cm3 and (31.75±1.96×12.05)cm3 respectively,the mean V30-CT and V30-MR were (39.29%±1.96×9.30)% and (47.73%±1.96×9.54)% respectively,and the mean D50-CT and D50MR were (2 716±1.96×220)cGy and (3 000±1.96×339)cGy respectively.Conclusion s The contoured volume based on MRI is more accurate than that based on CT.The main difference between them is at the deep leaf of the parotid,parotid duct and subparotid.Contouring the parotid based on CT image would miss some part of the parotid and would influence the accuracy of the V30 and D50 in some cases.%目的 对鼻咽癌调强放疗的患者,在调强放疗的计划设计中,分别以MR及CT作为标准,勾画腮腺,比较其所勾画的腮腺体积差别及其对三维调强适形放疗(IMRT)计划中腮腺DVH的影响.方法 2008年5月至2008年11月间,20例实施根治性调强放疗的鼻咽癌患者,在放射治疗前1周行MR及增强定位CT扫描,并输入OTP治疗计划系统.然后将20例患者的CT影像及MR影像随机分成4组,由4名放疗科医师分别勾画其腮腺范围.之后将同一患者的CT及MR图像进行融合,评价所勾画的腮腺的体积差异,以CT为标准进行调强放疗计划设计,然后对比两种影像所勾画的腮腺的DVH的差别.结果 以CT和MRI为参照标准勾画的腮腺平均体积分别为(24.53±1.96×7.23)、(31.75± 1.96×12.05)cm3 ;V30 分别为(39.29± 1.96×9.30)%、(47.73±1.96×9.54)%;D50分别为(2 716±1.96×220)、(3 000 ±1.96×339)cGy.结论 以MR为标准勾画腮腺范围及体积较为准确,其与CT之差异主要集中在腮腺深叶及腮腺管、副腮腺区.以CT为标准勾画腮腺可能"遗漏"部分腮腺范围,并可能影响IMRT计划中部分腮腺的V30及D50评价的准确性.