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. 2018 Sep 1;102(1):210-218.
doi: 10.1016/j.ijrobp.2018.04.060. Epub 2018 May 2.

Virtual Bronchoscopy-Guided Treatment Planning to Map and Mitigate Radiation-Induced Airway Injury in Lung SAbR

Narges Kazemzadeh  1 , Arezoo Modiri  1 , Santanu Samanta  1 , Yulong Yan  2 , Ross Bland  2 , Timothy Rozario  2 , Henky Wibowo  3 , Puneeth Iyengar  2 , Chul Ahn  2 , Robert Timmerman  2 , Amit Sawant  4
Affiliations

Virtual Bronchoscopy-Guided Treatment Planning to Map and Mitigate Radiation-Induced Airway Injury in Lung SAbR

Narges Kazemzadeh et al. Int J Radiat Oncol Biol Phys. .

Abstract

Purpose: Radiation injury to the bronchial tree is an important yet poorly understood potential side effect in lung stereotactic ablative radiation therapy (SAbR). We investigate the integration of virtual bronchoscopy in radiation therapy planning to quantify dosage to individual airways. We develop a risk model of airway collapse and develop treatment plans that reduce the risk of radiation-induced airway injury.

Methods and materials: Pre- and post-SAbR diagnostic-quality computerized tomography (CT) scans were retrospectively collected from 26 lung cancer patients. From each scan, the bronchial tree was segmented using a virtual bronchoscopy system and registered deformably to the planning CT. Univariate and stepwise multivariate Cox regressions were performed, examining factors such as age, comorbidities, smoking pack years, airway diameter, and maximum point dosage (Dmax). Logistic regression was utilized to formulate a risk function of segmental collapse based on Dmax and diameter. The risk function was incorporated into the objective function along with clinical dosage volume constraints for planning target volume (PTV) and organs at risk (OARs).

Results: Univariate analysis showed that segmental diameter (P = .014) and Dmax (P = .007) were significantly correlated with airway segment collapse. Multivariate stepwise Cox regression showed that diameter (P = .015), Dmax (P < .0001), and pack/years of smoking (P = .02) were significant independent factors associated with collapse. Risk management-based plans enabled significant dosage reduction to individual airway segments while fulfilling clinical dosimetric objectives.

Conclusion: To our knowledge, this is the first systematic investigation of functional avoidance in lung SAbR based on mapping and minimizing doses to individual bronchial segments. Our early results show that it is possible to substantially lower airway dosage. Such dosage reduction may potentially reduce the risk of radiation-induced airway injury, while satisfying clinically prescribed dosimetric objectives.

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Conflict of interest statement

Conflicts of Interest: Dr. Sawant has research support from the National Institutes of Health, Varian Medical Systems and VisionRT Ltd.

Figures

Figure 1
Figure 1
CT slices and segmented bronchial tree of a patient with a 5 cm diameter left-upper-lobe tumor. Pre-treatment (a) axial and (b) coronal slices along with (c) segmented airway tree. Post-SAbR (d) axial and (e) coronal CT slices along with (f) corresponding segmented airway tree, acquired 11 months after treatment. Red and yellow arrows indicate the tumor target and the distant fibrosis, respectively. The dashed line in b and e indicates the location of the fissure between the lobes.
Figure 2
Figure 2
A visual demonstration of the airway segments, in vicinity of PTV, that were considered in our study (PTV is shown in brown.)
Figure 3
Figure 3
Post-SAbR state of airway segments (collapsed/non-collapsed) as a function of Dmax and airway diameter. The lines indicate equal probabilities of collapse across various diameters and values of Dmax.
Figure 4
Figure 4
DVH curves for (left column) PTV, esophagus, spinal cord, heart and lung, and (right column) three airway segments ranging in diameter from 3–8 mm. Airway protection factors are (a) 10, (b) 20 and (c) 50. Solid lines correspond to plans that incorporated the risk model for airway segment collapse and dashed lines correspond to the original clinical plans that ignored dose to airway segments.
Figure 5
Figure 5
Dose color wash figures for one axial slide for the demonstrated plans in Figure 4. The airways are shown in brown and PTV is shown in red.
See this image and copyright information in PMC

References

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