Dosimetric study and suitable population between 3-and 2-dimensional brachytherapy for cervical cancer at different locations

Objective To investigate the effect of different uterine positions upon the dose distribution and target area conformability of organ at risk (OAR) and explore the population suitable for 2-dimensional brachytherapy by comparing the dosimetry between CT-guided 3-and 2-dimensional brachytherapy for cervical cancer. Methods Thirty patients with cervical cancer received 72 cycles of 3-dimensional brachytherapy and then 2-dimensional brachytherapy was designed. The deviation angle of the uterus from the longitudinal asix on the coronal and sagittal CT images was measured. The obtained data were divided into the A to D and the group Ⅰ to Ⅳ according to the deviation angle (T) of uterus position from the longitudinal axis on the sagittal CT images and the volume of HRCTV (VHRCTV) to identify the optimal uterine position and range of VHRCTV for 2-dimensional brachytherapy. Statistical analysis was performed by paired t-test. Results The deviation angle of uterine position was not significantly correlated with the target CI index or D90 of HRCTV in both brachytherapy plans (P value between 0.077-0.633), whereas it was positively correlated with the D2 cm3 of bladder (P value between 0.001-0.030) and negatively associated with the D2 cm3 of rectum in both 2-and 3-dimensional brachytherapy (P value between 0.011-0.016). In group B (|T|≤10°) and group Ⅲ(VHRCTVvalue between 86-96 cm3), the OAR parameters and CI index did not significantly differ between two brachytherapy plans (P value between 0.040-0.463), whereas varying degree of statistical differences was observed among other groups (P value between 0.000-0.940). Conclusions Although uterine position exerts no effect upon the conformal index of target area, it can affect the dose distribution of OAR. No statistical significance is noted in the dosimetry between 3-and 2-dimensional brachytherapy plans when the uterine position is almost flat (|T|≤10°) and the radiotherapy target area is appropriate (VHRCTVvalue between 86-96 cm3). In this situation, 2-dimensional brachytherapy is the optimal option. Key words: Cervical neoplasms/brachytherapy; Uterine positions; Dosimetry