Accurate needle placement is essential for effective cervical high dose-rate (HDR) brachytherapy in anatomically complex or asymmetric tumor regions. Conventional rigid obturators used with standard applicators, such as Elekta's Geneva and Venezia systems, lack the flexibility to reach off-axis targets, thereby limiting treatment precision. This study presents the development and validation of a manually operated steerable interstitial needle for gynecological brachytherapy. The device employs a compliant split-shaft mechanism that converts differential push-pull actuation into controlled tip deflection. Finite element analysis guided the selection of Grade 5 titanium and informed geometric optimization to balance flexibility with mechanical stability. A prototype was fabricated and integrated into a 3D-printed handheld actuation unit compatible with the Elekta Venezia applicator. Experimental evaluation in gelatin and silicone phantoms under computed tomography (CT) imaging demonstrated tip deflections of up to 33.0 mm with the Flexible Implant Tube 6F and up to 18.5 mm with the ProGuide 6F at an insertion depth of 80 mm. Placement accuracy remained within ± 5 mm in over 95\% of the trials. These results validate the steerable needle concept and highlight its potential to improve maneuverability during clinical brachytherapy.