胸中段食管癌复位前后靶区移位和剂量学变化的初步研究

摘要

目的:分析胸中段食管癌放疗复位前后靶区和剂量学变化,探讨胸中段食管癌放疗复位的必要性和可行性.方法:回顾性分析10例接受三维适形放疗的食管癌患者,食管靶区长度平均为11.7cm.对患者行CT扫描并勾画靶区(GTV1),放疗40 Gy后行CT复位模拟定位,并且重新勾画靶区(GTV2).制定两套计划,治疗计划1(Planl)按前半程追加处方剂量至60 Gy;治疗计划2(Plan2)将后半程与前半程进行图像刚性配准,总处方60 Gy,比较分析两次计划靶区几何位移和剂量学变化.结果:复位后的靶区(PTV)体积明显小于复位前(P=0.036).在同一横断面上x轴相差最大4mm,y轴相差最大2.3 mm,z轴相差最大6.0mm.PTV达到处方剂量的体积平均分别为97.45％±0.73％和95.19％±2.37％;靶区最大剂量、最小剂量和平均剂量差异均没有统计学意义.危及器官心脏、左肺和全肺的平均剂量以及脊髓最大点剂量复位后的计划均小于复位前计划(P＞0.05);右肺平均剂量复位后显著小于复位前(t=3.172,P=0.025).结论:胸中段食管癌放疗过程中靶区体积及解剖位置的变化等因素可能导致的靶区低剂量和正常组织的超量照射,实施CT重新扫描定位和调整治疗计划可以修正靶区剂量,减少不必要的正常组织的照射.%Objective: To analyze the target motion during the mid- thoracic esophageal carcinoma radiotherapy and discuss the dosimetry change. Methods: Ten patients with primary middle thoracic esopheal carcinoma were selected retrospectively. The mean length of target was 11.7 cm. Each patient received two CT scanning and declining GTV1 and GTV2 during the radiotherapy. The two CT images were rigid deformed.Physicist designed plans both in GTV1 and GTV2 and campared the target motion and dosimetry variation. Results: The targets of new CT (GTV2) were significantly smaller than those of old CT (GTV1). On the same transverse the maximal difference of x-axis,y-axis was 4 mm and 2.3 mm. The avarage volume of GTV1 and GTV2 which achieved the prescription dose was 99.45%±0.73% and 97.19%±2.37% respctively. There were no statistical diffetence for the maximal dose,mean dose and the minimal dose of the target. The new plan for the mean dose of heart,left lung,total lung and the maximum dose of spinal-cord were smaller than those of the old plan with no significant dierrence.But there was statistically difference for the mean dose of right lung (t=3.172,P=0.025). Conclusions: The target volume change and anatomic position displacement of mid-thoracic esophageal carcinoma should not be neglected in clinics. These changes would cause underdose in target and overdose in normal tissue. Therefore, it is necessary to have another CT scanning and replan during the mid-thoracic esophageal carcinoma radiotherapy.