Inconsistent definitions of local control for stereotactic body radiation therapy for early-stage lung cancer – A systematic review

INTRODUCTION: Assessments of local control (LC) following stereotactic body radiation therapy (SBRT) for early-stage non-small cell lung cancer (NSCLC) play a crucial role in evaluating treatment efficacy. However, there is significant variability in how LC is defined and assessed across studies, making it challenging to compare outcomes and establish standardized benchmarks. This heterogeneity impacts clinical decision-making, prognostic assessments, and interpretations of lung SBRT efficacy in both research and clinical practice. METHODS: A systematic review was conducted following PRISMA guidelines to identify criteria used in reporting post-SBRT local control (LC) rates. A comprehensive PubMed search identified studies published between 2006 and 2023 reporting LC or primary tumor control (PTC) rates following SBRT for early-stage NSCLC. Eligible studies were independently reviewed, and LC definitions were categorized based on the anatomical sites considered and the criteria used to define treatment site progression. RESULTS: Of 155 studies identified, 113 met the inclusion criteria. LC determinations were described as 'local control', 'local failure', 'local recurrence', or 'primary tumor control' in 39%, 32%, 24%, and 4% of studies, respectively. Anatomic sites assessed for LC included recurrence events outside of the primary tumor site in 32% of studies. These LC assessments included progression within the same lobe, ipsilateral lung, and regional nodes in 68%, 11%, 4%, and 2% of studies, respectively; 15% did not specify the anatomical location(s) evaluated. Articles published after 2021 were more restrictive and limited LC evaluations to PTC in 95.7%. Regarding PTC evaluations, 12 different criteria were used ranging from reporting the specific imaging modality used (CT or PET), growth threshold assessed by Response Evaluation Criteria in Solid Tumors (RECIST) or up to 50% increase in diameter, minimum growth duration (2-36 months or serial changes), or histopathological confirmation in 28%, 31%, 18%, and 1%, respectively. CONCLUSIONS: LC evaluations following lung SBRT have evolved away from considering progression events in the same lobe and regional lymph nodes. Studies reporting PTC rates often do not state the assessment methods used and utilize non-objective criteria that may not be reproducible. Future studies reporting post-SBRT LC rates should clearly state the anatomic sites considered, document the objective measures used for PTC assessments, and report the minimum duration of post-treatment surveillance to better inform future research aiming to improve post-SBRT monitoring strategies.