Program Information
3D Lung Tumor Position Verification During Breath-Hold Stereotactic Volumetric Modulated Arc Therapy
C Hazelaar1*, M Dahele1 , H Mostafavi2 , L van der Weide1 , S Keek1 , B Slotman1 , W Verbakel1 , (1) VU University Medical Center, Amsterdam, Noord-Holland, (2) Varian Medical Systems, Palo Alto, CA
Presentations
WE-RAM3-GePD-J(B)-4 (Wednesday, August 2, 2017) 10:30 AM - 11:00 AM Room: Joint Imaging-Therapy ePoster Lounge - B
Purpose: To evaluate if template matching+triangulation can determine lung tumor position during breath-hold stereotactic treatments.
Methods: On-board kilovoltage (kV) images, acquired at 7-11frames/s during irradiation of an anthropomorphic thorax phantom with 3 lung tumors, were enhanced using 1) bandpass filtering, and 2) 12° digital tomosynthesis (DTS)+bandpass filtering. 2D reference templates (filtered digitally reconstructed radiographs) were created from planning CT data. Normalized cross-correlation was used for optimal 2D matching between templates and enhanced kV images. For 3D verification, each registration was triangulated with multiple previous registrations (minimum stereo separation angle 12°, precluding 3D verification during first 12° of each breath-hold). Four stationary phantom datasets and two datasets simulating intra-breath-hold motion by gradually moving the couch were analyzed. Using phantom-derived software settings, kV images acquired during irradiation from 4 patients were analyzed off-line (3-7frames/s, n=13 breath-hold datasets, tumor volumes 2.1-8.5cm³).
Results: For the phantom, average root-mean-square errors (tracked-vs-known position) after bandpass filtering without/with couch movement were lateral 3.9/2.0mm, longitudinal 3.0/1.0mm and vertical 4.1/2.3mm with 3D position determined in on average 90.2/70.3% of the dataset (excluding the first 12°), and after DTS+bandpass without/with movement 0.3/0.4mm, 0.3/0.3mm, and 0.2/0.3mm with 3D position in 99.7/68.7% of the dataset. For patient data, the addition of DTS decreased average standard deviations (representing system precision and tumor motion) from lateral=7.8mm, longitudinal=1.8mm, and vertical=6.5mm to 1.3mm, 1.0mm, and 1.0mm, respectively (reduction range 1.5-15.6/0.1-2.2/1.1-11.9mm). 3D position without/with DTS was determined in 68.0%/74.4% of the dataset (average values, excluding first 12° of each breath-hold, range 42.6-96.5%/patient with DTS).
Conclusion: Phantom and clinical data support the addition of DTS to template matching+triangulation with bandpass filtering to identify 3D lung tumor position during breath-hold stereotactic irradiation. This methodology is suited to near-real time verification, however, further work is needed to increase the proportion of datasets in which 3D position can be accurately determined.
Funding Support, Disclosures, and Conflict of Interest: This work was sponsored by Varian Medical Systems
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