Room: Karl Dean Ballroom C
Purpose: Radiation injury to central and peripheral airways during lung stereotactic ablative radiotherapy (SAbR) is poorly understood and accounted for. Airways are critical to lung function, serving as conduits that enable alveolar gas exchange. Injury to airway segments can thus render downstream â€œfunctionalâ€? lung regions, dysfunctional. Here, we (i) use virtual bronchoscopy to map up to â‰¥13 generations of airways, (ii) use pre- and post-SAbR airway maps to estimate dose-response of individual airways, (iii) develop a population risk model for airway collapse, and (iv) use particle swarm optimization (PSO)-based inverse planning to create an IMRT plan that incorporates a patient-specific risk model for radiation-induced airway collapse.
Methods: Under IRB approval, a research virtual bronchoscopy system (Archimedes, Bronchus Inc.) was used to retrospectively segment individual airway elements from pre- and post-SAbR, diagnostic-quality CT scans from 3 lung cancer patients (total 648 airway segments). For each patient, open and collapsed segments, 8-12 months post-SAbR, were identified. A logistic regression-based collapse probability model was created as a function of max airway dose and mean airway diameter. The branching serial nature of the airway tree was considered in determining the relative importance of individual segments. Specifically, a weight was assigned to each segment, proportional to the number of functional downstream segments, enabling us to account for patient-specific, pre-treatment, co-morbidity-induced airway damage. A PSO-based IMRT plan was created for a patient with a central lung tumor (PTV:80cc), clinically treated with 10GyÃ—5Fx IMRT.
Results: Our proposed plan maintained PTV coverage and met clinical constraints while reducing dose by [max:71%, mean:15%] for airways <7mm and [max:40%, mean:5%] for airways â‰¥7mm. The overall weighted probability of airway collapse was reduced by 51%.
Conclusion: We demonstrated the feasibility of preserving post-SAbR respiratory function by quantitatively modeling dose response for and mitigating radiation injury to individual airway segments.
Funding Support, Disclosures, and Conflict of Interest: NIH grant R01CA202761