Computed tomography-based three-dimensional dosimetry of intracavitary brachytherapy for cervical cancer

Purpose. The aim of this study was to show the results of computed tomography (CT)-based dosimetry of intracavitary brachytherapy for cervical cancer. Materials and methods. A total of 20 patients with cervical cancer underwent intracavitary brachytherapy with external beam radiation therapy. The prescribed dose of brachytherapy was 6 Gy per fraction to point A. In every fraction a CT scan was performed after applicator insertion and three-dimensional (3D) dosimetry was done. The tumor dose was evaluated using D90 (the minimum dose delivered to 90% of the volume), and the doses of risk organs were evaluated using D2cc (the minimum dose in the most irradiated 2 cm(3) of the volume). Results. The mean D90 for the clinical target volume (CTV) was 7.0 Gy (range 4.8-9.8 Gy). There was a negative correlation between the volume and the D90 for the CTV. The mean D2cc doses for the rectum and bladder were 6.0 Gy (range 3.9-9.0 Gy) and 6.5 Gy (range 2.9-9.0 Gy), respectively. Conclusion. CT-based 3D dosimetry of intracavitary brachytherapy for cervical cancer was useful for evaluating the doses of the CTV and the organs at risk. In cases with a large CTV, CTV D90 was often lower than the point A dose, and modulation of the prescribed dose might have to be considered.