The Research Of MVCT Image-guided Internal Margin And Regression Of Uterus In Cervical Cancer During IMRT

Purpose:Radiotherapy for cervical cancer had the potencial to benefit from the use of IMRT and the healthy tissues around the tumor might accept lower dose.A more accurate external beam radiotherapy was needed.A reasonable margin must consider the internal organ motion.Too small margins might result in an underdosage of part of target volume, and big margins might result in the increasing of the volumes of the organs at risk, causing a more grave side effect.The purpose of this study is to quantify the internal margin and regression of uterus guided by MVCT in patients with cervical cancer and to correlate the movement of uterus with the change in bladder and rectum volumes.Method:Nine patients with cervical cancer underwent a MVCT exam before and daily during IMRT.245MVCT images were collected.Delineate the uterus, rectum and bladder and use the command "OR" to collect the variation of uterus.Internal margins of uterus were the distance between the boundaries of variation of uterus and every uterus in the six main directions and correlated with the regression of uterus, changes in the volumes of bladder and rectum.Result:Internal margins of uterus in superior, inferior, anterior, posterior, left lateral and right lateral directions were0.54、044、1.56、1.18、0.83and0.82cm.The regression of uterus were over30%after IMRT and changed significantly after the nineteenth treatment, mainly in S direction (p<0.001). The changes in the volumes of bladder and rectum correlated strongly with the movement of uterus, the former mainly in S direction (p<0.001),the latter mainly in P direction (p=0.001)Conclusion:The result of internal margin was reliable, but the two margins around CTV to PTV produced by correspponding fomulas were different.So the margins can not be practical applicated, and we have to quantify the setup errors in a prospective study.A planning CT was suggested to scan after the nineteenth treatment.When the bladder volume changes over100cc and the rectum volume changes over10cc should be on guard in the clinical treatment.