宫颈癌调强放疗中直肠体积与位置变化及对吸收剂量影响

Changes of rectal volume and location and their influence on rectal dose during the course of intensity-modulated radiotherapy of cervical cancer

目的探讨宫颈癌患者调强放疗（IMRT）中直肠体积与位置变化及对吸收剂量的影响。方法对随机选取10例宫颈癌根治性IMRT患者采集分次治疗前锥形束CT（CBCT）图像，与原始计划CT图像基于骨性解剖结构进行刚体配准，勾画出CBCT图像直肠轮廓并映射回原始计划CT图像，分析直肠体积与位置变化并评价直肠接受≥45Gy体积占总体积百分比（V45）改变。直肠体积与V帖相关性分析采用Spearman法。结果10例患者共采集227次CBCT图像进行分析，其中直肠体积变化为（35．0±7．3）～（97．7±14．7）cm^3，直肠中心位移左右方向为（0．14±0．06）cm、前后方向为（0．24±0．10）cm、头脚方向为（0．55±0．28）cm，直肠V45为（9．19±2．46）％～（60．54±11．67）％。直肠体积与V45相关性分析显示7例患者呈正相关（r=0．582～0．743，P值均〈0．01）；治疗中V45≤50％次数共68次，占30．0％。结论宫颈癌IMRT中直肠体积与位置及其实际吸收剂量在分次放疗间变化较大，大部分患者体积与V45之间呈正相关。

Objective To investigate the anatomical changes and dose variation of rectum during radiotherapy in patients with cervical cancer. Methods Ten patients with cervical cancer underwent intensity-modulated radiotherapy using online cone beam computed tomography （CBCT） before each fraction. Rectum was contoured on each CBCT and projected onto the planning CT to analyze the changes of the rectal volume and position. The rectal volume receiving ≥ 45 Gy （ V45 ） was evaluated accordingly. Results 227 CBCT images in 10 patients were collected. The rectal volume changed from （35.0 ± 7. 3 ） cm3 to （ 97.7 ± 14. 7 ） cm3. The shift of rectal center was （ 0.14 ± 0. 06 ） cm in left and right direction, （0.24 ±0. 10） cm in anterior and posterior direction, and （0.55 ± 0. 28 ） em in superior and inferior direction. The V45 of rectum varied from （9.19 ±2. 46） % to （60.54 ± 11.67） %. In 7 of the 10 patients, rectal volume and V45 of the rectum had significant positive correlation （ r = 0.582 - 0. 743, all P 〈 0. 01 ）. Among the 227 images, the V4s of rectum was ≤50% in 68 images （ 30. 0% ）. Conclusions Significant changes in rectal volume and position occurred during fractionated radiotherapy in patients with cervical cancer, which results in variations in the dose rectum received. For most patients, rectal volume and the V45 of rectum had significant positive correlation.