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

OBJECTIVE: To retrospectively compare 3-dimension (3D)-inverse planning optimization with 2 conventional planning methods in vaginal vault high-dose-rate brachytherapy.

METHODS: We randomly selected 26 patients with endometrium cancer, treated with external beam radiotherapy followed by intracavitary high-dose-rate 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, dose-volume-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.

RESULTS: Dose-volume-histogram analysis showed a significant difference (p<0.001) between the 3 treatment planning methods regarding clinical-target-volume 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 cm3 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.

CONCLUSION: 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.