Dose-volume histogram evaluation of prone and supine patient position in external beam radiotherapy for cervical and endometrial cancer

Abstract Background and purpose : To evaluate the influence of patient positioning on dose-volume histograms of organs at risk in external beam radiotherapy for cervical and endometrial cancer. Materials and methods : In 20 patients scheduled for definitive (7) or postoperative (13) external beam radiotherapy of the pelvis treatment planning CT scans were performed in supine and prone (belly board) positions. After volume definition of target and organs at risk treatment plans were calculated applying the four-field box technique. The dose-volume histograms of organs at risk were compared. Results : Radiotherapy in prone position causes a reduction of the bladder portion (mean 15%, p p p p =0.02) due to an anterior tumour/uterus movement, so that bowel portions within the 90% isodose are similar. The bladder filling correlates with a reduction of bladder and bowel (postoperatively treated patients) dose. Conclusions : External beam radiotherapy of the pelvis should be performed in prone position in postoperative patients because of best bowel protection. Considering the additional HDR brachytherapy rectum protection takes the highest priority in definitive treatment—the requirements are best met in supine position. An adequate bladder filling is important to reduce the irradiated bladder and bowel volumes.