鼻咽癌调强放疗中肿瘤和正常组织体积-剂量变化的研究

目的:研究鼻咽癌在调强放射治疗过程中，肿瘤和正常组织的体积、形态变化对各自剂量受量的影响。方法:2009年1月-2010年6月间初诊经病理明确诊断的鼻咽癌患者42例，所有患者经头颈肩膜固定行模拟CT，在CT图像上逐层勾画治疗靶区和正常组织，采用6MV X线9野共面调强放射治疗计划（IMRT）。鼻咽原发灶及颈部转移淋巴结照射剂量66Gy/30f/6w，鼻咽部和颈部淋巴引流区亚临床病灶照射剂量60Gy/30f/6w。治疗设备为西门子ONCOR直线加速器。治疗期间每日采集患者治疗体位0度和90度正交二维摄片图像，同原始计划DRR图像对比，在三维方向对患者进行摆位误差校正，然后实施放射治疗。每周采集一次患者治疗体位头颈部CT图像，把治疗计划按照标记点移植到每周CT上，重新进行计量计算，分析患者在治疗期间靶区及正常组织剂量分布变化。同步化疗采用多西他赛加顺铂方案，每三周一次，在放疗开始前1周内开始同步治疗。结果:所有患者放疗前GTV1平均体积39.19cc，GTV2平均体积16.59cc，放疗第4周及第6周GTV1平均退缩分别为26.41%、62.68%，GTV2平均退缩分别为28.43%、53.93%。治疗前双侧腮腺体积平均为24.16cc，放射治疗第4周，平均腮腺体积为19.04cc，第6周平均腮腺体积为17.54cc。正常组织计量受量方面，脊髓（D1%）、脑干（D1%）、颞叶（D1%）、内耳（Dmean）、腮腺（V30），原计划计量分别为:（41.2±0.98）Gy、（51.26±1.57）Gy、（59.95±2.11）Gy、（45.02±1.98）Gy、（47.87±18.05）%。照射第4周分别为:（44.09±1.88）Gy、（52.81±2.47）Gy、（62.04±2.43）Gy、（47.24±3.68）Gy、（49.03±15.68）%。第六周（44.44±2.7）Gy、（54.14±2.51）Gy、（62.34±2.86）Gy、（48.37±5.37）Gy、（52.19±15.51）%。结论:随着鼻咽癌调强放射治疗的进行，照射肿瘤靶区同原始计划剂量分布会有一定差异，除1例淋巴结退缩及病人消瘦等原因而造成外轮廓内收较大的患者以外，其余CTV实际照射剂量为处方剂量95%以上。正常组织在整个治疗过程所受照射剂量同原始计划比较有所增加。

Dose-volume study for tumor and normal tissue of nasopharyngeal carcinoma with IMRT

Objective:To study the change of dose distribution by the change of the volume and morphology of the tumor and the normal tissues through the process of the nasopharyngeal carcinoma IMRT.Methods:All 42 patients who were pathologically diagnosed as nasopharyngeal carcinoma from January 2009 to June 2010 were admitted.All patients underwent a simulation CT before the treastment，and the images were uploaded to the Xio treatment therapy system (TPS).The target volume and normal tissues were contoured on the CT image and then the treatment IMRT plan was developed using 6MVX，9 coplanar fields.The dose to the nasopharyngeal tumor and lymph node was 66Gy/30f/6w，dose to the nasopharynx subclinical lesions and neck lymphatic drainage area was 60Gy/30f/6w.Daily orthogonal images were acquired in the patient treatment position to compare with the DRR of the original treatment planning image，and the patient positionning error was corrected in three dimensions，then the radiation therapy was implemented.Each patient underwent a simulation CT scan weekly to analyse the dose distribution changes of the target and the normal tissues.Concurrent chemotherapy regimen was cisplatin plus docetaxel every 3 weeks，the chemotherapy was started before the beginning of the radiaotherapy.Results:The average volume of GTV1 was 39.19cc before radiotherapy，GTV2 was 16.59cc，at 4th and 6th week of the radiotherapy course the average reduction of GTV1 were 26.41%,62.68%，for GTV2 were 28.43%and 53.93%respectively.Before treatment，the average volume of bilateral parotid was 24.16cc，at 4th week of radiation therapy，the average volume of parotid was 19.04cc，at 6th week the average volume of the parotid gland was 17.54cc.For the does distribution to the normal tissues，in the original plan，spinal cord（D1%)，brainstem（D1%)，temporal lobe（D1%)，the inner ear（Dmean)，parotid gland（V30）are (41.2±0.98)Gy，(51.26±1.57)Gy，(59.95±2.11)Gy，(45.02±1.98)Gy，(47.87±18.05)% respectively，at 4th week of radiotherapy，they are (44.09±1.88)Gy，(52.81±2.47)Gy，(62.04±2.43)Gy，(47.24±3.68)Gy，(49.03±15.68)%，and at 6th week，(44.44±2.7)Gy，(54.14±2.51)Gy，(62.34±2.86)Gy，(48.37±5.37)Gy，(52.19±15.51)%.Conclusion:In the nasopharyngeal IMRT process，the actual dose distribution of the tumor will be some difference to the original plan，except one case whose outline contour changes relatively sever because of the shrinkage of the lymph node and the weight loss，the CTV actual dose is above 95%of the prescribed dose，although after a few weeks of treatment the tumor target volume and shape changes，the difference was not significant.The dose to the normal tissues in the whole course of treatment will be increased compared with the original plan.