Room: AAPM ePoster Library
Purpose: Functional lung avoidance radiotherapy aims to mitigate post-radiotherapy toxicity by spatially mapping lung function and generating treatment plans that preferentially spare high-functioning regions. A common limitation of current approaches is that they do not account for peripheral airways, which constitute a critical component of the conducting architecture that enables alveolar gas exchange. Therefore, dose avoidance strategies relying solely on functional mapping may potentially result in damage to the very conduits that serve the functional regions. Here, we propose a patient-specific, functionally weighted airway sparing (FWAS) method, which preferentially avoids excessive dose to airways connected to high-functioning lung regions.
Methods: High-resolution breath-hold CTs (BHCTs) and simulation 4DCTs were acquired from four lung stereotactic ablative radiotherapy (SAbR) patients. For each patient, the BHCT was input into a research virtual bronchoscopy software to autosegment ~12 generations of airways. The corresponding peak-exhalation and peak-inhalation 4DCT phases were used to estimate regional ventilation. For each terminal airway, total ventilation within the sublobar volume supported by that airway was estimated and, subsequently, used to calculate a weighting factor. Upstream airways were weighted based on the cumulative ventilation supported by corresponding downstream airway tree. Using our previously developed model for airway radiosensitivity (as a function of airway diameter), dose constraints were assigned to each airway as <5% probability of collapse. The airway functional weights and dose constraints, along with clinical dose constraints for PTV and organs at risk (OARs), were input to a swarm optimization–based inverse planning engine to generate the FWAS plan.
Results: FWAS plans showed superior performance to clinical plans in terms of airflow preservation (3-21% improvement) and ventilation preservation (3-23% improvement). Both plans satisfied PTV coverage and clinical OAR dose constraints.
Conclusions: These early findings suggest that preferentially sparing airways that serve high-functioning lung regions may be critical in preserving post-SAbR respiratory function.
Funding Support, Disclosures, and Conflict of Interest: This work is partially supported by the National Institutes of Health (R01 CA202761) and Varian Medical Systems.