食管癌简化调强放疗中靶体积变化及对初始计划剂量学影响

Study on relationship between the beginning plan and the anatomy and dosimetry change during intensity modulated radiotherapy for esophageal carcinoma

目的 探讨食管癌简化调强放疗（sIMRT）中解剖学动态变化规律和靶体积变化,以及这些变化对初始计划剂量学分布影响,评价重新修改放疗计划的必要性和时机.方法 29例接受单纯放疗的食管癌患者常规模拟CT扫描,其中11例在放疗开始后每2周扫描（每例4次）,18例在放疗第4周进行第2次扫描（每例2次）.将CT模拟图像与初始计划CT图像融合后由同一医生重新勾画靶区及正常器官,将初始计划导入新勾画的靶区,得出靶区及正常器官剂量学参数后与初始计划比较.结果 每2周扫描的11例忠者疗前和疗后第2、4、6周胸部轮廓体积变化平均值分别为13948cm3和13245、12789、11837 cm3（6周时t=2.07,P=0.043）,每2周体积缩小平均值为425 cm3.0～6周中大体肿瘤体积平均值逐渐降低,其中0周与4、6周比较下降最明显（47.22 cm3：37.78 cm3,t=2.44,P=0.035;47.22 cm3：33.55 cm3,t=2.55,P=0.029）,而4周和6周变化不明显（t=-0.75,P=0.261）.0～6周靶区适行指数逐渐降低和不均匀指数依次增加,分别为0.70、0.68、0.67、0.61（4周时t=3.20,P=0.013）和1.13、1.22、1.23、1.27（4周时t=-4.56,P=0.001）.全组患者sIMRT 4周时100%大体肿瘤受照剂量增加至62.57 Gy（t=-2.93,P=0.007）,99%临床靶体积受照剂量和95%计划靶体积受照剂量分别下降至58.24 Gy（t=1.49,P=0.147;2例＜54 Gy）和57.44 Gy（t=2.07,P=0.048）;正常组织中只有脊髓最大剂量和双肺V30的增加有统计学意义（41.52 Gy∶43.53Gy,t=-2.42,P=0.022;11.4%∶12.2%,t=-2.26,P=0.032）.结论 食管癌sIMRT4周时肿瘤体积变化最明显,是CT-CT融合观察靶体积变化的最佳时机.部分患者需要做二次计划的修改使肿瘤靶区获得合理剂量.

Objective To study the dynamic changes of anatomy and the dosimeter distribution those changes influenced. Methods Initially simplified intensity modulated radiation therapy （sIMRT）were performed to twenty-nine patients with phase Ⅲ - Ⅳa esophageal carcinoma from January 2007 to March 2009. The target volumes and involving organs were contoured on the primary spiral CT pictures.After sIMRT planning being finished, secondary CT scan was acquired to rectify the treatment center. For eleven patients at every other week and eighteen patients at the fourth week, spiral CT images were acquired according to the same treatment center, and thereafter fused with the first CT images. Firstly, the law of change and the best time of replanning were searched：the changed gross tumor volume （GTV）, gross node volume （GTVnd）, plan target volume （PTV） and normal organs （lung, spinal cord, heart and outline） on the fusion interface were modified by a single physician, the changes for each structure throughout treatment were measured by system software. Secondly, dose distributions were computed and evaluated for replanning CT using the same beams arrangement as the initial plan. Cumulative dose was estimated using weighted average and compared with the original plan. Results For eleven patients, The law of change：the volume of outlines and GTV gradually decreased, and the change come to peak in the fourth week. The conformal index for PTV gradually decreased, whereas the heterogeneous index gradually increased. For twenty-nine patients on the fourth week, the dose of GTV were more than 60 Gy. The dose of PTV-D95 and CTV-D99 decreased （ t = 1.49, P = 0. 147 and t = 2. 07, P = 0. 048 respectively）. The dose of CTV-D99 in two patients deceased to 54 Gy or less. The cord-Dmax and lung V30 increased significantly （ t = - 2. 42, P = 0. 022 and t = -2. 26,P =0. 032）. Conclusions During the course of sIMRT for esophageal cancer, the volume of GTV decreased and the change come to peak in the fourth week. It is the best time for evaluating the change of dose of target volume using CT-CT fusion. For some patients, revise of the treatment plan is needed to ensure adequate target volume dosage and safety of normal tissues.