Impact of the filling status of the bladder and rectum on their integral dose distribution and the movement of the uterus in the treatment planning of gynaecological cancer

Purpose: Determination of the impact of the filling status of the organs at risk (bladder and rectum) on the uterus mobility and on their integral dos e distribution in radiotherapy of gynaecological cancer. Methods: In 29 women suffering from cervical or endometrial cancer two CT s cans were carried out for treatment planning, one with an empty bladder and rectum, the second one with bladder and rectum filled. The volumes of the organs at risk were calculated and in 14 patients, receiving a definitive r adiotherapy, the position of the uterus within-the pelvis was shown using m ultiplanar reconstructions. After generation of a 3D treatment plan the dos e volume histograms were compared for empty and filled organs at risk. Results: The mobility for the corpus uteri with/without bladder and rectum filling was in median 7 mm (95%-confidence interval: 3-15 mm) in cranial/ca udal direction and 4 mm (0-9 mm) in posterior/anterior direction. Likewise, cervical mobility was observed to be 4 mm (-1-6 mm) mm in cranial/caudal d irection. A full bladder led to a mean reduction in organ dose in median fr om 94-87% calculated for 50% of the bladder volume (P < 0.05, Wilcoxon's ma tched-pairs signed-ranks test). For 66% of the bladder volume the dose coul d be reduced in median from 78 to 61% (P < 0.005) and for the whole bladder from 42 to 39% (P < 0.005). respectively. No significant contribution of t he filling status of the rectum to its integral dose burden was noticed. Conclusion: Due to the mobility of the uterus increased margins between CTV and PTV superiorly, inferiorly, anteriorly and posteriorly of 15, 6 and 9 mm each, respectively, should be used. A full bladder is the prerequisite f or an integral dose reduction. (C) 1999 Elsevier Science Ireland Ltd. All r ights reserved.