Study Of Image-guided Intensity-modulated Radiotherapy For Cervical Cancer Post Surgery

Objective To evaluate the intra-fractional and inter-fractional setup error and organ motion of the vagina in image-guided intensity-modulated radiotherapy for cervical cancer post surgery.And then to find out the proper clinical target volume to planning target volume margin.Methods Three cases stage Ib1 to Ib2 cervical cancer patients received radical hysterectomy and lymphadenectomy.And we placed five markers in vagina during the surgery.Took simulated CT scan for these patients post surgery and designed Intensity modulation radiation therapy(IMRT) and proceeded with image-guided IMRT.The patients received cone beam CT scan before and right after radiotherapy everyday.Matched the cone beam CT image before the radiotherapy with the simulated CT image by bone to get the interfractional setup error.And corrected the big setup error(＞3mm) on-line.Compared the cone beam CT image with the simulated CT image to acquire the interfractional motion of the five markers.Compared two cone beam CT images before and after the radiotherapy within the same day to acquire intrafractional movement and markers motion.Calculated the safety margin between CTV and PTV by the setup error and markers motion.Sketched bladder and rectum and calculated the volume change of them.Then analyze the relationship between them with the organ motion.Results Three patients received 131 cone beam CT scan during 51 fractions. And the on-line correction could obviously decrease setup error and the safety margin needed was 2.8 to 4.3mm.The safety margin for markers motion was 6.9 to 21.4mm.The margin in the post-anterior direction was the largest one.The safety margin for all the inter- and intrafactional factors was 8.4 to 21.9mm.The safety margin for vagina in left-right,superior-inferior and posterior-anterior directions were 15.4mm,20.3mm and 21.gmm respectively.The position changing of vagina was correlated with the volume changing of bladder.Conclusion The cone beam CT and on-line correction could reduce the setup error.The motion of vagina was large during the radiotherapy and it was correlated with volume changing of bladder.