宫颈癌HT中膀胱和/直肠充盈状态对其受量影响

Impacts of bladder and rectum filling status on their dosimetric parameters in helical tomotherapy for cervical cancer

目的比较宫颈癌HT分次治疗间膀胱和直肠体积与计划体积差异，评估膀胱和直肠充盈状态对其受量影响。方法选取2012-2016年于陆军总院行HT的宫颈癌患者20例。每次疗前行MVCT与计划CT图像配准后重新计算剂量分布并勾画肿瘤及膀胱、直肠并测量体积和位置。应用Planned Adaptive模块进行剂量重建，得到每幅MVCT图像和当次MVCT对应剂量．将融合MVCT图像及每幅MVCT图像所对应剂量分布传输至形变软件MIM6．0中进行剂量叠加得到总剂量，并与计划时所用KVCT的比较。组间比较采用配对t检验或方差分析。结果当膀胱体积差异值〉400ml或差异比〉60％时膀胱质心向脚、背向位移增大，Dmean和V50升高（P〈0．05）。当直肠体积差异值〉30ml或差异比〉30％时直肠质心向头、腹向位移增大，直肠V45和Vso升高（P〈0．05）．导致直肠受量增加。结论膀胱充盈状态对膀胱受量影响虽不大，但体积应控制在400ml或60％以内。定位与治疗时适度充盈膀胱更容易满足重复性，直肠充盈仅〉30ml或30％便会造成直肠剂量增加，保证直肠空虚状态可有效降低直肠受量。

Objective To analyze the changes in volume and the planning volume of the bladder and rectum during helical tomotherapy （HT） treatment for cervical cancer, and to evaluate the impacts of bladder and rectum filling on their dosimetric parameters. Methods Twenty patients with cervical cancer who received HT in our hospital from 2012 to 2016 were enrolled as subjects. Before treatment, megavoh computed tomography （MVCT） and registration of planning CT images were preformed to recalculate the dose distribution, delineate the target volume, and measure the volume and position of the bladder and the rectum. Each MVCT image and the corresponding single dose were obtained by dose reconstruction using the Planned Adaptive module in HT planning workstation. The fused MVCT images and the corresponding single dose for each MVCT were loaded to MIM Maestro software 6. 0 for close stacking. The obtained total radiation dose was compared with that obtained by kilovolt CT. Between-group comparison was made by paired t-test or analysis of variance. Results If the volume change in the bladder was more than 400 ml or the rate of volume change was higher than 60%, the displacements of the bladder eentroid toward the foot and dorsal sides were significantly increased ; the D and V50 were significantly increased （ P〈 0. 05 ）. If the volume change in the rectum was more than 30 ml or the rate of volume change was higher than 30%, the displacements of the rectum eentroid toward the head and ventral sides were significantly increased;the V45 and Vs0 for the rectum were significantly increased （P〈0. 05）. Conclusions Although the bladder filling status has little effect on the radiation dose to the bladder, the volume change or the rate of volume change should be no more than 400 ml or 60%, respectively. Moderately filled bladder is recommended for positioning and treatment ,which achieves satisfactory repeatability of the treatment. A volume change of more than 30 ml or a rate of volume change of higher than 30% can result in an increase in the dose to the rectum. Empty rectum can effectively reduce the dose to the rectum.