Stereotactic ablative body radiation therapy for treatment of ultra-central lung tumors: a narrative review.

Background and Objective: Stereotactic ablative radiotherapy (SABR) has become the standard treatment for medically inoperable peripherally and centrally located stage I non-small cell lung cancer (NSCLC). However, ultra-central (UC) lung tumors pose unique challenges due to their proximity to vital structures, resulting in heightened risks of severe toxic effects. Recent studies have made significant strides in advancing SABR for these challenging cases. This review aims to clarify the definitions of UC lung lesions, examine various SABR dose regimens, assess constraints for critical normal structures, and evaluate outcomes related to local control, overall survival and toxicity profile following SABR for lung lesions. Methods: We conducted a comprehensive literature search in PubMed and clinical trial information registered on ClinicalTrials.gov from January 2006 to September 2024. Existing definitions of UC lung lesions, SABR dose regimens and their corresponding treatment outcomes following SABR, SABR-related toxicities and constraints for critical organs at risk, and potential strategies to improve the application of SABR in UC lung tumors were summarized and reviewed. Key Content and Findings: Prior studies have adopted different definitions of UC lung tumors, and a range of SABR regimens has been applied. While favorable local control rates have been reported, SABR-related toxicities-particularly massive hemoptysis and esophageal complications-restrict its use in UC patients. There is a need for further clarification of optimal SABR schemes and constraints for critical organs at risk. Emerging strategies, such as proton SABR and the combination of SABR with immunotherapy, show promising potential for improving treatment outcomes. Conclusions: SABR is emerging as a promising treatment for patients with UC lung lesions. There is an urgent need for a standardized definition of UC tumors, which will guide prospective studies aiming at determining optimal regimens and validating constraints for critical normal organs. Other strategies, including proton SABR and the combination of SABR with immunotherapy, show great promise and are garnering enormous attention.