Association between daily step counts and frailty trajectory classes in lung cancer patients undergoing radiotherapy: a prospective longitudinal study.

PURPOSE: To characterize frailty trajectories in patients undergoing radiotherapy with lung cancer, identify factors associated with trajectory membership, and examine the association between daily step counts and frailty trajectories during radiotherapy. METHODS: In this prospective longitudinal study, daily step counts were collected via the WeChat Step Mini-program from the start to the end of radiotherapy. Frailty was assessed via the Frailty Phenotype Scale before radiotherapy, at the end of radiotherapy, and 1 month after radiotherapy. Latent class growth modeling was used to identify frailty-trajectory classes, and multinomial logistic regression was used to examine associated factors and the relationship between step counts and trajectory membership. RESULTS: Among 327 patients, three frailty trajectories were identified: prefrailty declining (56.58%), frailty stable increasing (27.83%), and severe frailty increasing (15.60%) group. After adjustment for demographic and clinical covariates, higher average daily step counts during radiotherapy were independently associated with a lower likelihood of membership in adverse frailty trajectories. CONCLUSIONS: Frailty trajectories in patients with lung cancer undergoing radiotherapy were heterogeneous. Step-count gradients were observed around 3000, 6000, and 9000 steps/day, suggesting exploratory thresholds for different frailty-risk intervals. IMPLICATIONS FOR CANCER SURVIVORS: Daily step counts are a scalable real-world metric. Combining continuous step monitoring with routine frailty screening may support early identification of high-risk patients and proactive, individualized management during and after radiotherapy.