Heterogeneity of study endpoints in stereotactic body radiation therapy studies for bone metastases: A systematic...

This systematic review evaluated variability in study endpoints among stereotactic body radiation therapy (SBRT) studies for bone metastases. Heterogeneity in endpoint definitions and reporting may hinder cross-study comparability and the establishment of consistent treatment protocols.

A comprehensive search of Ovid MEDLINE, Embase, and the Cochrane Central Register of Controlled Trials identified prospective studies, including cohort studies, phase I/II trials, and randomised controlled trials (RCTs), published between 2014-01-01 and 2024-11-12. Studies were eligible if they: (1) included adult patients with bone metastases treated with SBRT, (2) were prospective, and (3) reported pre-defined clinical endpoints.

A total of 58 studies were included: eight cohort studies, 37 phase I/II trials, and 13 RCTs. Pain-related endpoints were the most frequently reported primary endpoints, with pain response reported in 28% (16 studies). Other primary endpoints included toxicities (22%, 13 studies), survival metrics (12%, seven studies), and local control (9%, five studies). Secondary endpoints varied, with survival-related endpoints reported in 60% (35 studies) and toxicity in 41% (24 studies). Endpoint selection differed by clinical scenario, reflecting distinct objectives such as symptom relief, local control, and progression-free survival. Variability in definitions for endpoints, particularly pain flare and vertebral compression fracture, along with inconsistent radiological response criteria, was noted.

Considerable heterogeneity in endpoint selection, definitions, and measurement tools across SBRT reflects diverse clinical objectives. Consensus-driven standardisation of endpoints, response criteria, and follow-up schedules is essential to enhance comparability, facilitate evidence synthesis, and support integration of SBRT research findings into clinical practice.