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Abstract
For Stereotactic Body Radiation Therapy (SBRT) treatment of lung and liver, we quantified the differences between two image guidance methods: 4DCT and ExacTrac respiratory‐triggered imaging. Five different patients with five liver lesions and one lung lesion for a total of 19 SBRT delivered fractions were studied. For the 4DCT method, a manual registration process was used between the 4DCT image sets from initial simulation and treatment day to determine the required daily image‐guided corrections. We also used the ExacTrac respiratory‐triggered imaging capability to verify the target positioning, and calculated the differences in image guidance shifts between these two methods. The mean (standard deviation) of the observed differences in image‐guided shifts between 4DCT and ExacTrac respiratory‐triggered image guidance was left/right (L/R)=0.4(2.0)mm, anterior/posterior (A/P)=1.4(1.7) mm, superior/inferior (S/I)=2.2(2.0) mm, with no difference larger than 5.0 mm in any given direction for any individual case. The largest error occurred in the S/I direction, with a mean of 2.2 mm for the six lesions. This seems reasonable, because respiratory motion and the resulting imaging uncertainties are most pronounced in this S/I direction. Image guidance shifts derived from ExacTrac triggered imaging at two extreme breathing phases (i.e., full exhale vs. full inhale), agreed well (less than 2.0 mm) with each other. In summary, two very promising image guidance methods of 4DCT and ExacTrac respiratory‐triggered imaging were presented and the image guidance shifts were comparable for the patients evaluated in this study.PACS number: 87.55.ne
Highlights
258 Wang et al.: Two Stereotactic Body Radiation Therapy (SBRT) image guidance methods slow blurred scan, Cone-beam computed tomography (CBCT) is not the ideal way to visualize tumor to determine image guidance shifts
The ExacTrac respiratory-triggered mode has been previously presented in the literature for SBRT treatment of liver and lung tumors.(18,19) Here we report our experience in using these two methods (i.e., 4DCT and ExacTrac respiratory-triggered imaging), and we quantify the differences in imageguided shifts between these two methods
We report the difference between full exhale and full inhale derived image guidance for ExacTrac respiratory-triggered images, and present our findings on pre- and post-treatment shifts when using ExacTrac triggered imaging
Summary
258 Wang et al.: Two SBRT image guidance methods slow blurred scan, CBCT is not the ideal way to visualize tumor to determine image guidance shifts. In order to address this issue, some researchers are working on respiratory-correlated 4D CBCT for better appreciation of the tumor motion at the time of treatment setup, and producing more comparable image series with the original simulation 4DCT scan. Such technologies have not yet been made commercially available.(16,17). In addition to acquiring an initial simulation 4DCT used for definition of the ITV, we routinely acquire a ‘control’ image guidance 4DCT scan in the CT suite immediately prior to each treatment fraction for comparison with the simulation-derived ITV This comparison is used to derive the required image guidance shifts. We report the difference between full exhale and full inhale derived image guidance for ExacTrac respiratory-triggered images, and present our findings on pre- and post-treatment (i.e., intrafractional) shifts when using ExacTrac triggered imaging
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