膀胱直肠管理对前列腺癌靶区及OAR剂量影响

Effects of bladder and rectum management on dose distributions of target and organs at risk in intensity-modulated radiotherapy for prostate cancer

目的：应用IGRT技术观察膀胱、直肠在治疗中变化，分析其对治疗影响。方法入选18例接受根治性IMRT的前列腺癌患者，共行CBCT在线校正治疗体位247次。在模拟CT和CBCT图像上勾画CTV、膀胱及直肠，观察膀胱、直肠体积和位置变化。将x、y、z轴方向平移摆位误差引入TPS中重新计算得到PTV、膀胱体积（ BV）、直肠体积（ RV）等剂量体积参数，分析各参数对治疗的影响。对再计划与原计划结果行配对t检验，采用Pearson相关法分析膀胱、直肠位移和膀胱、直肠体积对靶区受量影响。结果治疗过程中膀胱和直肠充盈度有较大变化，其中原计划与再计划PTVD95％为7777．37 cGy ∶7628．56 cGy （P＝0．027），PTV Dmin为87．91 cGy ∶83．35 cGy （P＝0．000），RVP 为5．89％∶8．31％（ P＝0．000）。 PTVD95％与膀胱、直肠移动具有相关性（ r＝0．296、0．177）。直肠体积与PTVD95％有一定相关性（ r＝0．115）。对PTV Dmin而言，除上述各指标之外，与膀胱体积有一定相关性（ r＝？0．128）。结论在前列腺癌IMRT中，使膀胱、直肠尤其是后者尽量复原定位时状态对保证靶区受量及减少直肠受照有明显意义。

Objective To observe the motions of the rectum and bladder by image？guided radiotherapy （ IGRT） and to analyze their impact on treatment. Methods Eighteen patients with prostate cancer undergoing intensity？modulated radiotherapy （ IMRT） were enrolled in the study and 247 cone？beam computed tomography （ CBCT） images were obtained from this study. The clinical target volume, bladder, and rectum were contoured on all simulated CT and CBCT to examine their volume and position changes. The dose distributions were recalculated based on the data of the x？, y？, and z？axis setup errors. The doses to planning target volume （ PTV） and organs at risk were calculated in the replanning, and their impact on treatment was analyzed. Comparison of the planning and replanning results was made by paired t？test. The effects of displacements and volumes of the bladder and rectum on target doses were analyzed by Pearson correlation method. Results Great changes in the volumes of the bladder and rectum were observed during the treatment. For the planning and replanning results, PTVD95% was 7777. 37 cGy vs. 7628. 56 cGy （ P=0. 027）, PTV Dmin was 87. 91 cGy vs. 83. 35 cGy （P=0. 000）, and RVP was 5. 89% vs. 8. 31%（P=0. 000）. There were correlations between PTVD95% and the motions of the bladder and rectum, with correlation coefficients of 0. 296 and 0. 177, respectively. The correlation coefficient between rectal volume and PTVD95% was 0. 115, indicating a certain correlation. There is a certain correlation between and PTV Dmin and bladder volume, with a correlation coefficient of？0. 128. Conclusions The recovery of the state during localization for the bladder and rectum, especially the latter, has great significance to ensure the target dose and reduce exposure of the rectum in the IMRT for prostate cancer.