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Virtual Bronchoscopy-Guided Risk-Management Based Treatment Planning to Mitigate Radiation-Induced Airway Injury in Lung SAbR

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N Kazemzadeh

N Kazemzadeh1*, A Modiri1 , M Hamzeei1 , A Hagan1 , T Rozario2 , Y Yan2 , H Wibowo3 , J Yu3 , R Timmerman2 , A Sawant1 , (1) University of Maryland School of Medicine, Baltimore, MD, (2) UT Southwestern Medical Center, Dallas, TX, (3) Broncus Medical, Inc., San Jose, CA


WE-G-FS1-9 (Wednesday, August 2, 2017) 4:30 PM - 6:00 PM Room: Four Seasons 1

Purpose: Post-treatment radiation injury to the bronchial tree is an important yet poorly understood potential determinant of toxicity in lung stereotactic ablative radiotherapy (SAbR). Here, we introduce a treatment planning method where injury to individual airway segments is incorporated using population-based risk models. Using these models, we develop treatment plans that reduce the risk of radiation injury to these structures in order to preserve post-SAbR lung function.

Methods: In a retrospective study of 26 lung cancer patients, the relation between individual segment collapse and patient variables including Dmax and segment diameter were evaluated. Using a virtual bronchoscopy software (Broncus, San Jose, CA), the bronchial tree was autosegmented, exported as a RT structure to a treatment planning system (Eclipse, Varian), and the dose to individual airway segments from the clinically planned beams was computed. Univariate analysis showed that segmental diameter (p=0.014) and Dmax (p=0.007) were significantly correlated with segmental collapse. Logistic regression was utilized to calculate the probability function of segmental collapse based on Dmax and diameter. A treatment plan was created using an in-house GPU-based particle swarm optimization engine. The objective function consisted of dose volume constraints on OARs (Organ at Risk) and PTV (Planning Target Volume), and the weighted summation of probabilities of segmental collapse. The weights were defined as segmental diameter multiplied by a constant value named Airway Protection Factor (APF).

Results: Risk-management-based plans considerably reduced dose to individual airway segments while fulfilling the clinical dosimetric objectives for PTV and OARs. Reduction in Dmax to airways with diameter 3, 5 and 8 mm was as follows: APF=10 (14.9%,15.5%,13.2%); APF=20 (8.0%,9.2%,14.0%); APF=50 (9.6%,13.6%,14.5%).

Conclusion: Our results show that risk-management based plans may reduce airway injury and, thereby, post-SAbR toxicity through significant dose reduction to individual airway segments while satisfying volume dose constraints on PTV and other OARs.

Funding Support, Disclosures, and Conflict of Interest: This research was supported by NIH R01 CA202761 grant.

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