Markerless 3D tumor tracking during single-fraction free-breathing 10MV flattening-filter-free stereotactic lung radiotherapy

I. F. Remmerts de Vries*, Max Dahele, Hassan Mostafavi, Ben Slotman, Wilko Verbakel

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review


Background and purpose: Positional verification during single fraction lung SBRT could increase confidence and reduce the chance of geographic miss. As planar 2DkV imaging during VMAT irradiation is already available on current linear accelerators, markerless tracking based on these images could offer widely available and low-cost verification. We evaluated treatment delivery data and template matching and triangulation for 3D-positional verification during free-breathing, single fraction (34 Gy), 10 MV flattening-filter-free VMAT lung SBRT. Methods and materials: Tumor tracking based on kV imaging at 7 frames/second was performed during irradiation in 6 consecutive patients (7 lesions). Tumor characteristics, tracking ability, comparison of tracking displacements with CBCT-based shifts, tumor position relative to the PTV margin, and treatment times are reported. Results: For all 7 lesions combined, 3D tumor position could be determined for, on average, 71% (51–84%) of the total irradiation time. Visually estimated tracked and automated match +/− manually-corrected CBCT-derived displacements generally agreed within 1 mm. During the tracked period, the longitudinal, lateral and vertical position of the tumor was within a 5 mm/3 mm PTV margin 95.5/85.3% of the time. The PTV was derived from the ITV including all tumor motion. The total time from first set-up imaging to end of the last arc was 18.3–31.4 min (mean = 23.4, SD = 4.1). Conclusion: 3D positional verification during irradiation of small lung targets with limited motion, was feasible. However, tumor position could not be determined for on average 29% of the time. Improvements are needed. Margin reduction may be feasible. Imaging and delivery of a single 34 Gy fraction was fast.
Original languageEnglish
Pages (from-to)6-12
Number of pages7
JournalRadiotherapy and Oncology
Publication statusPublished - 1 Nov 2021

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