PlannerRFT: Reinforcing Diffusion Planners through Closed-Loop and Sample-Efficient Fine-Tuning. - Hongchen Li; Tianyu Li 004; Jiazhi Yang; Haochen Tian 001; Caojun Wang; Lei Shi; Mingyang Shang; Zengrong Lin; Gaoqiang Wu; Zhihui Hao; Xianpeng Lang; Jia Hu 003; et al. (CoRR, 2026)