子宫颈癌图像引导放疗不同时期分次内误差的研究

Intrafractional setup errors in image guided radiation therapy of cervical carcinoma at different treatment stages

目的通过直线加速器自带的锥形束CT(cone beam CT,CBCT)采集的图像信息研究子宫颈癌图像引导放射治疗(image guided radiation therapy,IGRT)疗程中不同时期分次内误差的变化规律。方法 20例行IGRT治疗的子宫颈癌患者在疗程的初期(放疗开始第1周内)、中期(放疗开始第2～3周)和后期(放疗开始第4～5周)采用CBCT扫描分别获得X轴(左右)、Y轴(头脚)、Z轴(前后)、绕X轴旋转、绕Y轴旋转和绕Z轴旋转6个方向上的治疗前、后摆位分次内误差,并对不同时期的分次内误差进行LSD多重比较。结果 20例子宫颈癌患者IGRT疗程初期、中期和后期3个时期共获得180次(各60次)分次内误差。在X轴、Y轴和绕X轴旋转方向上,初期和后期分次内误差均高于中期[(0. 26±0. 14) cm、(0. 24±0. 13) cm vs (0. 19±0. 10) cm,(0. 30±0. 20) cm、(0. 29±0. 20) cm vs (0. 19±0. 11) cm,(1. 38±0. 53)°、(1. 37±0. 65)°vs (1. 10±0. 90)°,均P <0. 05]。Z轴方向上,初期分次内误差高于中期[(0. 19±0. 18) cm vs (0. 14±0. 10) cm,P <0. 05]。结论子宫颈癌IGRT疗程中X轴、Y轴和绕X旋转方向上,初期和后期分次内误差较中期大,Z轴方向初期较中期大,这为自适应放疗靶区外扩边界和合理安排CBCT扫描时间提供依据。

Objective To study the changes of intrafractional setup errors in image guided radiation therapy( IGRT) of cervical carcinoma at different stages of the treatment via linear accelerator’s cone-beam CT( CBCT). Methods Twenty cases of cervical carcinoma treated with IGRT were enrolled. The intrafractional setup errors were collected at the Xdirection( left to right),Y-direction( head to foot),Z-direction( anterior to posterior),X-axis rotation,Y-axis rotation and Z-axis rotation at prime-term( within a week of radiation therapy),medium-term( second to third week from the beginning of radiation therapy),and later term( fourth to fifth week from the beginning of radiation therapy). Multiple LSD comparisons were then carried out at multiple stages. Results A total of 180 intrafractional setup errors were collected at primeterm,medium-term and later term( 60 times each term) from 20 cervical carcinoma patients treated by IGRT. On X-direction,Y-direction and X-axis rotation,the intrafractional setup errors at the prime-term and the later term were higher than that of the medium-term (( 0. 26 ± 0. 14) cm and( 0. 24 ± 0. 13) cm vs( 0. 19 ± 0. 10) cm,( 0. 30 ± 0. 20) cm and( 0. 29 ± 0. 20) cm vs( 0. 19 ± 0. 11) cm,( 1. 38 ± 0. 53) ° and( 1. 37 ± 0. 65) ° vs( 1. 10 ± 0. 90) °,all P < 0. 05)Moreover,on the Z-axis,the intrafractional setup error at the prime-term was higher than that of the medium-term (( 0. 19 ±0. 18) cm vs( 0. 14 ± 0. 10) cm,P < 0. 05)Conclusion For cervical cancer treated by IGRT,the intrafractional setup errors of the prime-term and the later term were higher than that of the medicum term on the X-axis,the Y-axis and X-axis rotation,whereas on the Z-axis,the intrafractional setup errors of the prime-term was higer than that of the medium-term.This finding provides information for how to reduce the planning target volume margin in adaptive radiotherapy and to arrange the CBCT scan time reasonably.