锥形束CT宫颈癌调强放疗中膀胱充盈程度对膀胱实际剂量及靶区影响的评估

Evaluation of the effect of bladder filling degree on the actual dose and target area of bladder in cone beam CT intensity modulated radiotherapy for cervical cancer

目的探讨锥形束CT(CBCT)宫颈癌调强放疗中患者治疗当次膀胱充盈程度的不同,其当次治疗时对膀胱实际照射剂量以及对靶区的影响,为膀胱剂量的准确评估及放射治疗前膀胱准备提供基础。方法选取我院2019年1月~2019年12月采用调强放疗技术的宫颈癌患者10例,由同一名放疗科医生在CT图像以及CBCT图像上勾画膀胱及靶区,分别比较膀胱质心变化以及膀胱实际剂量学变化参数并分析原因,并在不同剂量条件下统计其漏照靶区的体积。结果随着膀胱体积的增大,膀胱质心与上下方向、前后方向的相关系数分别为0.964、0.678,差异均有统计学意义(P<0.05),与左右方向相关系数为0.165,差异无统计学意义(P=0.242);随着膀胱体积的增大,V 30、V 40、V 50、D mean都呈减小的趋势,其相关系数分别为0.872、0.805、0.593、0.795,差异均有统计学意义(P<0.05);当膀胱体积的变化超过200mL时,靶区的漏照体积明显增加(P<0.05)。结论宫颈癌患者在放疗中膀胱充盈程度的一致性较差,从而导致靶区位移与膀胱在实际治疗时照射剂量的变化,所以放疗定位前应记录好患者尿量,在治疗前采用膀胱容量测量仪测量尿液体积,相对于定位时膀胱体积的变化应不超过200mL为宜。

Objective To study the actual dose changes of bladder in the treatment of cervical cancer and the effect on the target area according to bladder filling degree in patients with intensity-modulated radiotherapy,and provide a basis for accurate evaluation of bladder dose and bladder preparation before radiotherapy.Methods From January 2019 to December 2019,10 cervical cancer patients with intensity-modulated radiotherapy were selected.The bladder and the target area were delineated by the same radiotherapy doctor on the CT and cone beam CT(CBCT)image.The changes of bladder centroid and its dosimetric change parameters were compared and the reasons were analyzed.The volume of missed radiotherapy target area was counted under different dose conditions.Results With the increase of bladder volume,the correlation coefficients of bladder centroid with superior-inferior and anterior-posterior directions were 0.964,0.678,and all had statistically significant(P<0.05).The correlation coefficient with left-right direction was 0.165,and without statistically significant(P=0.242).With the increase of bladder volume,V 30,V 40,V 50 and D mean had decrease trend,the correlation coefficient was 0.872,0.805,0.593,0.795,and all have statistically significant(P<0.05).As the bladder volume changed more than 200mL(P<0.05),the volume of missed radiotherapy target area was obvious increased.Conclusion The consistency of bladder filling degree in patients with cervical cancer during radiotherapy is poor,resulting in the change of target displacement and bladder irradiation dose during actual treatment.Therefore,the urine volume of patients should be recorded before radiotherapy positioning.Before treatment,the urine volume should be measured by bladder volume meter,and the change of bladder volume relative to positioning should not exceed 200ml.