Room: Karl Dean Ballroom C
Purpose: Lung functional avoidance (LFA) planning aims to map and spare higher-functioning lung regions. A critical yet overlooked aspect is radiation injury to peripheral airways which serve as gas conduits to and from functional lung. While airways may appear as â€œlow-functioningâ€? regions with current functional-mapping techniques, radiation-induced airway damage can result in downstream functional loss. In this work we use (i) virtual bronchoscopy to map central and peripheral airways in lung stereotactic ablative radiotherapy (SAbR) patients, (ii) 4DCT to map regional ventilation, (iii) develop a model that estimates the contribution of each airway to regional ventilation, and (iv) use this model to create SAbR plans that aim to preserve lung function.
Methods: Under IRB approval, the airway tree of a lung SAbR patient was auto-segmented from a breath-hold CT, using a research version of a commercial virtual bronchoscopy system (Archimedes, Broncus Inc.). A ventilation map was generated from the planning 4DCT using the VESPIR (VEntilation via Scripted Pulmonary Image Registration) toolkit. For each terminal airway, the total ventilation within the volume supported by that airway was calculated and used as an airway weighting factor. Upstream airways were weighted based on the cumulative volumetric ventilation supported by corresponding downstream airways. We incorporated these function-based scores into a swarm optimization-based inverse planning engine to generate a 11-field IMRT plan.
Results: Regional ventilation was important determining the relative importance of various airways. E.g., for comparable diameter/hierarchy, airways supporting a higher cumulative ventilation were preferentially spared compared to those supporting lower cumulative ventilation. Using highly-parallelized swarm optimization it was possible to incorporate airway and ventilation maps while meeting clinical dose constraints.
Conclusion: Radiation injury to the airway tree is a critical factor that needs to be combined with ventilation maps in order to improve the ability of LFA planning to preserve post-SAbR lung function.
Funding Support, Disclosures, and Conflict of Interest: NIH R01CA202761