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- Title
Less intra-observer variation in fiducial marker registration compared to tumor registration in lung stereotactic body radiotherapy (SBRT).
- Authors
Persson, G. F.; Aznar, M.; Rosenschöld, P. M. A.; Engelholm, S. A.; Specht, L.; Josipovic, M.
- Abstract
Purpose: Radio-opaque fiducial markers are used as surrogates for position of mobile tumors in beam tracking or gating in lung and liver stereotactic radiotherapy. Usually set-up is done image-guided with conebeam computed tomography and tumor registration. In this study we investigated the performance of marker versus tumor registration in image-guidance and evaluated the stability of the marker within the tumor. Methods: We prospectively included 15 patients referred for lung SBRT. A complex fiducial marker was implanted by per-cutaneous puncture a week before planning. Voluntary deep inspiration breathhold scans (BHCT) (3 mm slice thickness) were acquired at planning and the three treatment days. The treatment days' BHCTs were registered to the planning BHCT to determine intra-observer uncertainty for both tumor and marker registration. All registrations were performed twice to determine intra-observer uncertainty in both tumor and marker registration. Differences between tumor and marker based image registrations of the BHCTs were evaluated from four possible combinations of tumor and marker based image registrations. Deviation in registration differences in the three translational directions quantified the marker stability. Results: One of the patients coughed up the marker between implantation and planning. Therefore only fourteen patients could be evaluated. Four patients had pneumothorax after the marker implantation, three needed a chest tube. Intra-observer uncertainties for image registration of tumor were -0.2 ± 0.9 mm (mean ± SD) in left-right (LR) direction, 0.0 ± 0.9 mm in anterior-posterior (AP) direction, 0.2 ± 1.0 mm in cranio-caudal (CC) direction and 1.2 ± 1.1 mm in three dimensions (3D). Intra-observer uncertainties for image registration of markers were -0.0 ± 0.3 mm in LR, 0.5 ± 0.5 mm in AP, 0.1 ± 0.7 mm in CC and 0.7 ± 0.5 mm in 3D. Mean 3D differences for tumor registrations on all days were significantly larger than for 3D marker registrations (p=0.007; paired t-test). Mean deviations between tumor and marker position of four registration combinations ranged -2.9 to 2.6 mm in LR, -0.8 to 1.5 mm in AP and -2.6 to 2.8 mm in CC. Four patients had deviations exceeding 2 mm in one or more registrations throughout the SBRT course. Conclusions: The intra-observer uncertainty in marker registration was significantly smaller than for tumor registration and the marker deviations were within the magnitude of the intra-observer variation. Therefore marker match can safely be used for image guidance during a short course of SBRT. Disclosure: No significant relationships.
- Subjects
TUMOR treatment; STEREOTACTIC radiotherapy; TREATMENT of lung tumors; LIVER tumors; COMPUTED tomography
- Publication
Journal of Radiosurgery & SBRT, 2013, Vol 2, p110
- ISSN
2156-4639
- Publication type
Article