Dose-Volume Histogram Analysis in Point A-based Dose Prescription of High-dose-rate Brachytherapy for Cervical Carcinoma

Traditionally, cervical brachytherapy has been prescribed to point A. However, since the Groupe Europ?en de Curieth?rapie and European Society for Radiotherapy＆ Oncology guidelines were published, image-guided brachytherapy has become an emerging technique. The purpose of this study was to evaluate the high-risk clinical target volume （HR-CTV） coverage and analyze dose-volume histograms for organs at risk in point A prescription of high-dose-rate brachytherapy. A total of 68 patients with locally advanced cervical cancer were treated with three-dimensional conformal external beam radiation therapy and brachytherapy from December 2012 to March 2017. Fractions of 6Gy for a total of 12-24Gy were delivered at point A by brachytherapy to all patients. Following each brachytherapy application, a pelvic computed tomography scan was performed and imported into a three-dimensional brachytherapy treatment planning system. In this study, the HR-CTV, bladder, and rectum were re-delineated according to Report 89 of the International Commission on Radiation Units and Measurements using the magnetic resonance images at the time of diagnosis, and the dose-volume histogram of each structure was analyzed. The median age of patients at diagnosis was 67 years （range, 31-91 years）. Mean HR-CTV D90 for all patients was 558.3cGy （range, 228.7-1005.1cGy） and the mean HR-CTV D90 within each clinical T stage was: Ib, 646.4cGy; 2a, 579.3cGy; 2b, 545.2cGy; 3a, 556.6cGy; 3b, 451.3cGy; and 4, 497.9cGy. HR-CTVD90 was correlated with HR-CTV. The mean D2cm3 was 678.1cGy for the bladder and 511.9cGy for the rectum. Using point A-based dose prescription, HR-CTV coverage was insufficient, especially in cases with a large tumor volume or a high T stage. Image-guided brachytherapy is expected to improve HR-CTV coverage while keeping rectal and bladder doses within acceptable levels