Feasibility of markerless 3D position monitoring of the central airways using kilovoltage projection images: Managing the risks of central lung stereotactic radiotherapy. Issue 2 (November 2018)

• Record Type: Journal Article
• Authors: Hazelaar, Colien; van der Weide, Lineke; Mostafavi, Hassan; Slotman, Ben J.; Verbakel, Wilko F.A.R.; Dahele, Max
• Is Part Of: Radiotherapy and oncology. Volume 129:Issue 2(2018)
• Page Start: 234
• Page End: 241
• Publication Date: 2018-11
• Subjects: Motion monitoring -- Positional verification -- Tracking -- Proximal bronchial tree -- Lung tumor -- Intra-fraction motion; Oncology -- Periodicals; Radiotherapy -- Periodicals; Tumors -- Periodicals; Medical Oncology -- Periodicals; Neoplasms -- radiotherapy -- Periodicals; Radiotherapy -- Periodicals; Radiothérapie -- Périodiques; Cancérologie -- Périodiques; Tumeurs -- Périodiques; Electronic journals; 616.9940642
• DOI: 10.1016/j.radonc.2018.08.007
• Languages: English
• ISSNs: 0167-8140

Abstract

Highlights: Central airways are a dose-limiting organ-at-risk for stereotactic lung radiotherapy. The position of the airways is typically not verified during irradiation. We report a technique for high-frequency markerless 3D airway position monitoring. It is based on continuous kV imaging, template matching, and triangulation. It can be implemented on a standard LINAC with no extra hardware. Abstract: Background and purpose: Central lung stereotactic body radiotherapy (SBRT) can cause proximal bronchial tree (PBT) toxicity. Information on PBT position relative to the high-dose could aid risk management. We investigated template matching + triangulation for high-frequency markerless 3D PBT position monitoring. Materials and methods: Kilovoltage projections of a moving phantom (full-fan cone-beam CT [CBCT, 15 frames/second] without MV irradiation: 889 images/dataset + CBCT and 7 frames/second fluoroscopy with MV irradiation) and ten patients undergoing free-breathing stereotactic/hypofractionated lung irradiation (full-fan CBCT without MV irradiation, 470–500 images/dataset) were retrospectively analyzed. 2D PBT reference templates (1 filtered digitally reconstructed radiograph/°) were created from planning CT data. Using normalized cross-correlation, templates were matched to projection images for 2D position. Multiple registrations were triangulated for 3D position. Results: For the phantom, 2D right/left PBT position could be determined in 86.6/75.1% of the CBCT dataset without MV irradiation, and 3D position (excluding first 20° due to the minimum triangulation angle) in 84.7/72.7%. With MV irradiation, this was up to 2% less. For right/left PBT, root-mean-square errors of measured versus "known" position were 0.5/0.8, 0.4–0.5/0.7, and 0.4/0.5–0.6 mm for left–right, superior–inferior, and anterior–posterior directions, respectively. 2D PBT position was determined in, on average, 89.8% of each patient dataset (range: 79.4–99.2%), and 3D position (excluding first 20°) in 85.1% (range: 67.9–99.6%). Motion was mainly superior–inferior (range: 4.5–13.6 mm, average: 8.5 mm). Conclusions: High-frequency 3D PBT position verification during free-breathing is technically feasible using markerless template matching + triangulation of kilovoltage projection images acquired during gantry rotation. Applications include organ-at-risk position monitoring during central lung SBRT.