###### Abstract  
Brachytherapy is an important technique to increase the overall survival of cervical cancer patients. However, a possible shift of the applicators in relation to the target and organs at risk may occur between imaging and treatment. Without daily adaptive brachytherapy planning, these applicator displacements can lead to a significant change in dose distribution. In order to resolve it, a robust optimization method had been developed using a genetic algorithm combined with a median absolute deviation as a robustness evaluation function. The resulting robustness plans from our strategy might be worth considering according to the GEC-ESTRO guidelines. From the point of view of dose delivery uncertainty from applicator displacement, the robust optimization may be considered with caution in a single-plan approach for High Dose Rate brachytherapy treatment planning and should be confirmed by a more thorough investigation. robust optimization; cervical cancer; high dose rate brachytherapy; single plan approach; median absolute deviation +
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for a more precise configuration of the dose to the target and the optimization of dwell times [10]. Excellent results were achieved with brachytherapy in combination with EBRT although this approach is not without limitations. The dose distribution in brachytherapy has a sharp dose gradient that is inherent to the radioactive source, and it is more sensitive to uncertainties of patient setup and applicator position [11]. Uncertainties in brachytherapy for cervical cancer are mainly related to source calibration, dose and dose-volume-histogram (DVH) calculation, reconstruction of applicators, contouring, intra- and inter-fraction uncertainties and dose delivery [12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22]. For the definition of the size and location of the cervical cancer, magnetic resonance imaging (MRI)/computed tomography (CT)-guided High Dose Rate (HDR) brachytherapy is currently defined by Groupe European de Curietrapie and the European Society for Radiotherapy and Oncology (GEC-ESTRO) as MR imaging prior to the first fraction of irradiation with the applicator in place and subsequent treatment planning of each fraction [23]. However, an MRI is not routinely available in radiotherapy departments and this optimal approach requires a large amount of personnel, time and equipment infrastructure. An alternative to using CT or radiographs for subsequent fractions is the use of one implantation for several fractions of irradiation with a standardized constant bladder filling [24; 25]. In the view from above, the dosimetric impacts of uncertainty should be considered to minimize therapy delivery variations and to improve patient outcomes: [PERSON] et al. [26] investigated the interfractional tandem displacement between multiple insertions, and found a displacement of about 1.2 cm in the caudal-cranial direction when a point A based-plan was generated on orthogonal X-rays, and [PERSON] et al. [27] applied one brachytherapy plan for several fractions and demonstrated that the average relative standard deviation for 13 series of 3 to 6 fractions were 15 and 17.5% for the rectum and bladder, respectively. [PERSON] et al. [25] compared individual MRI-based 3D treatment planning for each of four fractions with the use of only one MRI treatment plan for 14 patients. They found significant mean differences the brachytherapy dose of 9-28% variations. Applicator displacements especially occurred randomly during interfraction treatments so that the change-of-dose distribution could not be determined mathematically. For that reason, a robust optimization method may be considered to address uncertain conditions. There were many ways to deal with this uncertainty [28; 29; 30]; however, there is no direct literature minimizing dose delivery uncertainty by applicator displacements.