The benefit of Beam's eye view based 3D treatment planning for cervical cancer

Purpose: The aim of this study was to evaluate the possibility of Beam's ey e view (BEV) based three dimensional (3D) treatment planning, to reduce por tions of organs at risk included in the treated volume without increasing t he risk of geographical miss in external beam therapy of cervical cancer. Materials and methods: Three dimensional dose distribution of BEV based 3D treatment plans was compared to the 3D dose distribution derived from a fou r-field-box-technique using standard portals. A total of 20 patients with c ervical cancer stage FIGO IIB and FIGO IIIB was included. Dose distribution in the target volumes and in the organs at risk of BEV based treatment pla nning, was compared to the dose distribution of the standard field techniqu e using dose-volume-histograms. Results: In 4/20 patients (20%) a geographical miss at the cervix uteri was observed for the standard field technique. The BEV based treatment plannin g resulted in an adequate coverage of target volume and additionally in a r eduction of portions of bladder and bowel Volume included in the treated vo lume (-13.5, -10%). In contrast the BEV based technique resulted in an incr ease of portions of the rectum volume included in the treated volume compar ed to standard portals due to a shift of the rectum by the enlarged cervix uteri from its posterior to a lateral position. An overall 7% reduction of treated volume was observed, although the maximum width of lateral fields i ncreased for the BEV technique. Moreover, we have found a remarkable impact of bladder fillings on the amount of bowel and bladder volume included in the treated volume. Conclusion: BEV based 3D treatment planning for external beam therapy of ce rvical cancer offers a possibility to avoid geographical miss of part of th e CTV with reduced portions of bladder and bowel volume included in the tre ated volume. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.