Three-dimension anatomy-based planning optimization for high dose rate vaginal vault brachytherapy

ABSTRACT

To retrospectively compare 3-dimension [3D]-inverse planning optimization with 2 conventional planning methods in vaginal vault high-dose-rate brachytherapy. We randomly selected 26 patients with endometrium cancer, treated with external beam radiotherapy followed by intracavitary high-doserate brachytherapy. The study was carried out in the Radiotherapy Unit of King Abdulaziz University Hospital, Jeddah, Saudi Arabia between July 2010 and October 2011. For each brachytherapy fraction, dosevolume-histograms were analyzed for 3 different dose prescription protocols 0.5 cm from the applicator's tip, 0.5 cm along the applicator's surface, and inverse planning. Dose-volume-histogram analysis showed a significant difference [p<0.001] between the 3 treatment planning methods regarding clinical-targetvolume prescribed dose coverage 26.7% +/- 5.4% versus 48.5% +/- 6.7% versus 68.6% +/- 7.5%. The doses received by the volumes of 2 cm[3] of organs-at-risk were [p<0.001] rectum 4.6 +/- 1.1 Gy versus 2.8 +/- 0.5 Gy versus 3.3 +/- 0.5 Gy; sigmoid 1.4 +/- 0.8 Gy versus 0.7 +/- 0.3 Gy versus 0.9 +/- 0.5 Gy; and bladder 3.7 +/- 1.0 Gy versus 2.3 +/- 0.5 Gy, versus 2.7 +/- 0.6 Gy. Three-dimension inverse planning provides the ability to balance the target dose coverage against the sparing of organs at risk. For vaginal vault high-dose-rate inverse planning brachytherapy, the use of a CT scan only for the first fraction of treatment is feasible, and the dosimetric impact is minimal.