SU-E-T-404: A Prototype Program for Analyzing 4D Image Guidance Shifts for Lung SBRT.

PURPOSE A prototype in-house program was developed to assist deriving image guidance shifts clinically using our 4DCT method for lung SBRT. METHODS Our in-house prototype program was implemented in MATLAB. The 4D DICOM CT dataset of interest is imported by the program from AW and subsequently accepts input from the user regarding the desired relative IGRT shifts. The DICOM header information defining the relative 4D dataset origin is then read in and the desired relative IGRT shifts are applied to re-define the origin for the dataset that is to be shifted. Lastly, the redefined (shifted) origin coordinates are written to the header of the 4D dataset and the dataset is then exported to AW as DICOM files. We used this program to process 4DCT datasets for four patients with 3-5 fractions each. The clinical shifts that were derived previously, without this program, were applied to the images and the acceptability of these shifts were evaluated. RESULTS All slices and planes of the shifted 4D dataset were reviewed and, in general, demonstrated acceptable re-centering of the target within the ITV. However, it is noted that some small adjustments to the shift coordinates would likely have been made had we had the opportunity to visualize the shifted 4D dataset as facilitated by the new in-house software. The additional adjustments for the four patient cases studied here had an average of lmm and maximum of 2mm in three principle directions. We look forward to exploring the potential for implementing this software into our clinical workflow, and we believe that such a workflow is worthy of consideration by vendors for implementation as an available feature in future versions of their software. CONCLUSIONS We presented a prototype program to shift 4DCT image set for lung SBRT applications and demonstrated four clinical cases.