膀胱自主充盈状态对直肠癌术后三维适形放疗靶区和器官的影响

摘要

目的：研究在直肠癌术后三维适形放疗中，对比膀胱自主充盈状态和排空状态下靶区和周边重要器官体积改变以及照射剂量变化。方法临床8例直肠癌患者（Ⅱ/Ⅲ期），均由术后病理确诊，无严重合并症，行三维适形放疗。CT定位前1 h、30 min口服稀释造影剂各500 mL ，采用俯卧位及有孔腹部定位板进行膀胱自主充盈状态和排空状态下CT全盆腔定位扫描。对2次CT图像分别勾画直肠癌靶区和周围重要器官轮廓，三维计划设计。分析比较临床靶体积（CTV）、计划靶体积（PTV）、膀胱、股骨头和盆腔小肠体积，CTV、PTV、膀胱、股骨头和盆腔小肠平均照射剂量，对比2种状态下40 Gy膀胱、30 Gy股骨头和盆腔小肠最大照射剂量时各器官结构体积变化以及照射剂量差别。结果膀胱充盈使体积增加了569．31％，分别为（137±9）、（777±58）m L （ P＜0.05）；盆腔小肠体积减少28．95％，分别为（616±34）、（868±15）mL（P＜0.05）；CTV、PTV、股骨头的变化差异无统计学意义（ P＞0.05）。充盈时膀胱受照剂量为排空时的75．20％，分别为（3215±68）、（4275±169）cGy （ P＜0．05）；盆腔小肠受照剂量下降了46．61％，分别为（2719±173）、（1452±74）cGy（P＜0.05）；CTV、PTV、股骨头的变化差异无统计学意义（ P＞0.05）。40 Gy膀胱体积因膀胱充盈减少了55．58％（ P＜0.05），盆腔小肠最大照射剂量为排空状态下的81．15％（ P＜0.05）），30 Gy股骨头的变化差异无统计学意义（ P＞0.05）。结论直肠癌术后三维适形放疗中膀胱自主充盈状态对膀胱体积有影响，与膀胱排空相比膀胱充盈能减少膀胱、盆腔小肠照射剂量，对膀胱、盆腔小肠起一定保护作用。%Objective To study postoperative rectal cancer with three-dimensional conformal radiation ther-apy (3DCRT ) ,we tried distribution to the target and surrounding critical organs .Methods Eight cases of postop-erative rectal cancer with stage pT 1-3 N0-1 M0 were studied .All patients received 3DCRT and inferior seminal vesi-cle .One hours before CT simulation ,the bladder was first self-filled ,and then 500 mL of oral contrast solution was given at every half hour before the CT scan .The patient lay prone on the belly board and start to scan .Ure-thral catheterization was used for voiding or filling the bladder .Two sets of transverse images were taken for the whole pelvis in empty and full bladder .After the target and critical organs (bladder ,pelvic small bowel ,and femo-ral heads)were contoured ,a treatment plan of 3DCRT was made using the electrical precise PIAN treatment plan-ning system(TPS) .The volume and mean doses of CTV ,PTV ,bladder ,femoral heads ,and pelvic small bowel with the bladder empty and full were evaluated .The percentage of volume which received 40 Gy in the bladder ,30 Gy in the femoral heads ,and the maximal dose to the pelvic small bowel were also assessed and dose distribution in these targets or organs was compared between the empty and full bladder status .Results Comparing to the bladder empty status ,full bladder led to mean increase of 569 .31% in the bladder volume ,(137 ± 9) ,(777 ± 58) mL( P <0.05);and pelvic small bowel was reduced by 28 .95% ,in the volume ,(616 ± 34) ,(868 ± 15)mL( P <0.05);respectively ,no volume change was found in the CTV ,PTV and femoral heads( P>0.05) .The mean dose to the bladder in full status was 75.20% of that in empty status ,(3 215 ± 68) ,(4 275 ± 169)cGy( P <0 .05);re-spectively ,The mean dose to the pelvic small bowel was reduced by 46 .61% in the full bladder status ,(2 719 ± 173) ,(1 451 ± 74)cGy( P<0 .05);respectively ,no volume change was found in the CTV ,PTV ,femoral heads ( P>0.05).Fromemptytofull,dosevolumehistogram(DVH)comparisonshowed55.58% reductioninthepercent-age of bladder which received 40 Gy( P <0.05) ,The maximal dose to the pelvic small bowel in the full bladder status was 81 .15% of the empty status( P <0.05) ,without change in femoral heads( P >0.05) .Conclusion When treating rectal cancer with 3DCRT ,the filling status of bladder would result in the change of bladder vol-ume .Distended bladder is able to reduce the irradiation dose to the bladder ,pelvic small bowel ,thus brings up a better protection to these organs.