基于扇形束CT研究不同固定体位下宫颈癌术后放疗中膀胱体积改变对膀胱和小肠受照剂量的影响

目的:利用扇形束CT（FBCT）探讨宫颈癌术后放疗患者在不同固定体位下，膀胱体积的改变对膀胱、小肠的剂量学影响。方法:选取在中山大学肿瘤防治中心接受术后放疗的宫颈癌患者共22例，其中俯卧位固定患者10例，仰卧位固定患者12例，每次治疗前使用联影直线加速器uRT-linac 506c进行kV级FBCT，在放疗计划系统中对平移校正后的FBCT图像完成智能勾画，并复制原计划参数进行剂量计算。分析患者放疗过程中的膀胱体积变化趋势以及膀胱体积改变对膀胱和小肠受照剂量的影响。结果:22例患者在放疗过程中分次间膀胱体积与原计划膀胱体积均有不同程度的变化，且随着治疗进程，涨尿能力总体呈减弱趋势。仰卧位固定患者膀胱V45改变与膀胱体积变化率呈低度负相关（r=-0.431），膀胱V40、V30改变与膀胱体积变化率呈中度负相关（r=-0.651、r=-0.780），小肠V45、V40改变与膀胱体积变化率呈中度负相关（r=-0.701、r=-0.794），小肠V30改变与膀胱体积变化率呈高度负相关（r=-0.871）。而俯卧位固定患者膀胱V30改变与膀胱体积变化率呈低度负相关（r=-0.306），小肠V45改变与膀胱体积变化率呈低度负相关（r=-0.336），小肠V40、V30改变与膀胱体积变化率呈中度负相关（r=-0.505、r=-0.589）。结论:宫颈癌术后放疗患者治疗过程中分次间的膀胱体积与计划时的膀胱体积较难保持一致。相比于俯卧位固定，仰卧位固定患者的膀胱体积变化对其膀胱及小肠受照剂量的影响更大。

Effects of bladder volume variation on doses to bladder and small bowel in postoperative radiotherapy for cervical cancer in different patient positioning: an analysis based on FBCT

Abstract: Objective To investigate the dosimetric effect of bladder volume variation on bladder and small bowel in postoperative radiotherapy for cervical cancer in different patient positioning using fan beam computed tomography (FBCT). Methods A total of 22 cervical cancer patients who received postoperative radiotherapy in Sun Yat-sen University Cancer Center were retrospectively analyzed, including 10 patients in prone position and 12 patients in supine position. Before the treatment, kV FBCT was performed with UIH uRT-linac 506c accelerator. FBCT images after translational correction were automatically contoured in the treatment planning system, and the original plan parameters were copied for dose calculation. The trend of bladder volume variations and its effects on doses to bladder and small bowel were analyzed. Results The bladder volume of 22 patients changed to varying degrees during treatment. The urination ability showed a decreasing trend with the treatment course. For patients in supine position, the rate of bladder volume variations had a low negative correlation with V45 change of bladder (r=-0.431), moderate negative correlations with V40 and V30 changes of bladder (r=-0.651, r=-0.780) and V45 and V40 changes of small bowel (r=-0.701, r=-0.794), and a high negative correlation with V30 change of small bowel (r=-0.871). For patients in prone position, the rate of bladder volume variation had low negative correlations with V30 change of bladder and V45 change of small bowel (r=-0.306, r=-0.336), and moderate negative correlations with V40 and V30 changes of small bowel (r=-0.505, r=-0.589). Conclusion It is difficult to maintain the consistency of inter-fraction bladder volume in postoperative radiotherapy for cervical cancer, and the doses to bladder and small bowel are more affected by bladder volume variation in supine position as compared with prone position.