Inter-application displacement of brachytherapy dose received by the bladder and rectum of the patients with inoperable cervical cancer

BACKGROUND: The aim of the study was to examine on the CT basis the inter-application displacement of the positions D(0.1cc), D(1cc) and D(2cc) of the brachytherapy dose applied to the bladder and rectum of the patients with inoperable cervical cancer. PATIENTS AND METHODS: This prospective study included 30 patients with cervical cancer who were treated by concomitant chemo-radiotherapy. HDR intracavitary brachytherapy was made by the applicators type Fletcher tandem and ovoids. For each brachytherapy application the position D(0.1cc) was determined of the bladder and rectum that receive a brachytherapty dose. Then, based on the X, Y, and Z axis displacement, inter-application mean X, Y, and Z axis displacements were calculated as well as their displacement vectors (R). It has been analyzed whether there is statistically significant difference in inter-application displacement of the position of the brachytherapy dose D(0.1cc), D(1cc) and D(2cc) of the bladder and rectum. The ANOVA test and post-hoc analysis by Tukey method were used for testing statistical importance of differences among the groups analyzed. The difference among the groups analyzed was considered significant if p < 0.05. RESULTS: There are significant inter-application displacements of the position of the brachytherapy dose D(0,1cc), D(1cc) and D(2cc) of the bladder and rectum. CONCLUSIONS: When we calculate the cumulative brachytherapy dose by summing up D(0,1cc), D(1cc) and D(2cc) of the organs at risk for all the applications, we must bear in mind their inter-application displacement, and the fact that it is less likely that the worst scenario would indeed happen.