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. 2012 Jun 8:7:81.
doi: 10.1186/1748-717X-7-81.

Accuracy and inter-observer variability of 3D versus 4D cone-beam CT based image-guidance in SBRT for lung tumors

Reinhart A Sweeney  1 , Benedikt Seubert, Silke Stark, Vanessa Homann, Gerd Müller, Michael Flentje, Matthias Guckenberger
Affiliations

Accuracy and inter-observer variability of 3D versus 4D cone-beam CT based image-guidance in SBRT for lung tumors

Reinhart A Sweeney et al. Radiat Oncol. .

Abstract

Background: To analyze the accuracy and inter-observer variability of image-guidance (IG) using 3D or 4D cone-beam CT (CBCT) technology in stereotactic body radiotherapy (SBRT) for lung tumors.

Materials and methods: Twenty-one consecutive patients treated with image-guided SBRT for primary and secondary lung tumors were basis for this study. A respiration correlated 4D-CT and planning contours served as reference for all IG techniques. Three IG techniques were performed independently by three radiation oncologists (ROs) and three radiotherapy technicians (RTTs). Image-guidance using respiration correlated 4D-CBCT (IG-4D) with automatic registration of the planning 4D-CT and the verification 4D-CBCT was considered gold-standard. Results were compared with two IG techniques using 3D-CBCT: 1) manual registration of the planning internal target volume (ITV) contour and the motion blurred tumor in the 3D-CBCT (IG-ITV); 2) automatic registration of the planning reference CT image and the verification 3D-CBCT (IG-3D). Image quality of 3D-CBCT and 4D-CBCT images was scored on a scale of 1-3, with 1 being best and 3 being worst quality for visual verification of the IGRT results.

Results: Image quality was scored significantly worse for 3D-CBCT compared to 4D-CBCT: the worst score of 3 was given in 19 % and 7.1 % observations, respectively. Significant differences in target localization were observed between 4D-CBCT and 3D-CBCT based IG: compared to the reference of IG-4D, tumor positions differed by 1.9 mm ± 0.9 mm (3D vector) on average using IG-ITV and by 3.6 mm ± 3.2 mm using IG-3D; results of IG-ITV were significantly closer to the reference IG-4D compared to IG-3D. Differences between the 4D-CBCT and 3D-CBCT techniques increased significantly with larger motion amplitude of the tumor; analogously, differences increased with worse 3D-CBCT image quality scores. Inter-observer variability was largest in SI direction and was significantly larger in IG using 3D-CBCT compared to 4D-CBCT: 0.6 mm versus 1.5 mm (one standard deviation). Inter-observer variability was not different between the three ROs compared to the three RTTs.

Conclusions: Respiration correlated 4D-CBCT improves the accuracy of image-guidance by more precise target localization in the presence of breathing induced target motion and by reduced inter-observer variability.

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Figures

Figure 1
Figure 1
Comparison of image-quality in 3D-CBCT and 4D-CBCT for all 21 cases and 6 observers individually.
Figure 2
Figure 2
Correlation between the motion magnitude of the pulmonary target and differences between the image-guidance techniques using 4D-CBCT (IG-4D) and 3D-CBCT (IG-ITV and IG-3D).
Figure 3
Figure 3
Correlation between the motion magnitude of the pulmonary target and inter-observer variability using the IG-ITV technique.
Figure 4
Figure 4
Examples of image quality in 3D-CBCT and 4D-CBCT. The arrow indicates the position of the target. a) Small target in the upper lobe with a 3D motion amplitude of 9.3 mm, where averaged image quality was 3.0 and 1.8 in 3D-CBCT and 4D-CBCT, respectively. b) Target in the lower lobe immediately superior to the diaphragm with a 3D motion amplitude of 16.6 mm, where averaged image quality was 3.0 and 1.3 in 3D-CBCT and 4D-CBCT, respectively.
See this image and copyright information in PMC

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