Brachytherapy with two vaginal ovoids: CT imaging planning for each insertion or based on initial plan?

Aims. The aim of this study is to explore, on the basis of CT (computer tomography), imaging distribution of the brachytherapy dose at the organs at risk applied by two vaginal ovoids and explore whether there is the need for CT based planning after every insertion. Methods. Twenty-eight patients with cervical and endometrial cancer were treated at the University Clinical Center Tuzla at the Department of Radiotherapy, Clinical hospital for oncology, hematology and radiotherapy, in the period year 2009-2010. The patients were irradiated by a tanscutaneous radiotherapy dose of 45 Gy in 25 fractions to the pelvis. During transcutaneous radiotherapy, the patients started with intracavitary brachytherapy which was executed by vaginal ovoids applicators, once a week at HDR (high dose rate) with Ir-192 by Flexitron with the dosage of 4 x 6 Gy (TD 24 Gy). The brachytherapy dosage was prescribed at 0.5 cm from the surface of vaginal ovoids. After the first and third brachytherapy application, the position of applicators was verified based on CT imaging, and delineation of the bladder and the rectum was done. The aforementioned software was used for planning isodose distribution for the first and third application. Student's t-test was used for testing statistical importance (alpha=0.05) of the differences between the groups examined. Results. The effect of a maximum dose to the bladder and the rectum for the first and third insertion is not of a statistically significant difference (80, 4% vs. 77, 3%, P=0, 28; 92, 6% vs. 100, 3%, P=0, 09), respectively. A total maximum effect of the brachytherapy dose to the bladder was 18.76 Gy or 78.16% on the average, whereas its effect to the rectum was 22.7 Gy or 94.5%. Conclusions. The effect of a maximum brachytherapy dose for OAR for two vaginal ovoids, verified on the basis of computer tomography, can be precisely optimized in case CT imaging is done for every insertion. CT imaging should be performed for every brachytherapy insertion with two vaginal ovoids and it must not be planned for every following insertion on the basis of the initial plan.