A dosimetric study of 3D intracavitary brachytherapy in combination with applicator-guided IMRT boost for cervical cancer

Objective: To evaluate the dosimetric, feasibility of three-dimensional (3D) intracavitary brachytherapy in combination with applicator-guided intensity-modulated radiation therapy (IMRT) boost for patients with locally advanced cervical cancer who have unfavorable topography following external beam irradiation. Methods: A total of 7 patients with locally advanced cervical cancer who had unfavorable topography following external beam irradiation were included. Two plans were generated for brachytherapy using Oncentra 4.3 treatment planning system: 3D intracavitary brachytherapy and 3D intracavitary brachytherapy in combination with applicator-guided IMRT boost. To further evaluate cumulative doses to organs at risk (OAR) in the four fractions of combined plans, two methods were used: simple dose-volume histograms (DVH) parameter addition and deformable image registration (DIR)-based DVH accumulation. The D₉₀, V₁₀₀, and conformity index (CI) were evaluated. The paired t-test or Wi1coxon signed rank test was used for statistical analysis. Results: Compared with the 3D plan, the combined plan yielded higher D₉₀, V₁₀₀, and CI (P = 0.000), but showed no significant difference in D_2cc of the rectum, sigmoid colon, and bladder (P > 0.05). There were also no significant differences in D_2cc of the rectum, sigmoid colon, and bladder calculated by the two methods for calculating OAR cumulative doses, simple DVH parameter addition and DIR-based DVH accumulation (P > 0.05). Conclusions: For patients with cervical cancer who have unfavorable topography following external beam irradiation, 3D intracavitary brachytherapy in combination with applicator-guided IMRT boost can improve target coverage and CI, without increasing OAR doses. DIR-based DVH accumulation and simple DVH parameter addition may be both acceptable for assessing OAR cumulative doses. (authors)