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Comparison of Initial Patient Setup Accuracy Between Surface Imaging and Three Point Localization: A Retrospective Analysis

D Stanley

DN Stanley1*, AN Gutierrez1,2 , N Kirby1 , S Stathakis1 , D Saenz1 , N Papanikolaou1 , K Rasmussen1 (1) University of Texas Health Science Center San Antonio, San Antonio, Texas 78229 USA. (2) Miami Cancer Institute, Baptist Hospital, Miami, FL 33176 USA.


SU-H2-GePD-J(A)-2 (Sunday, July 30, 2017) 3:30 PM - 4:00 PM Room: Joint Imaging-Therapy ePoster Lounge - A

Purpose: Historically, the process of positioning a patient prior to imaging verification used a set of permanent patient marks or tattoos placed subcutaneously. After aligning to these tattoos, plan specific shifts are applied and the position is verified with x-ray imaging. Due to a variety of factors, these marks may deviate from the desired position or it may be hard to align the patient to these marks. With the increasing use of surface based imaging systems, an alternative method of verifying initial positioning relies on the entire skin surface and not just tattoos. The aim of this study was to retrospectively compare the 3D corrections of patients positioned with tattoos and with C-RAD CatalystHD.

Methods: A total of 2400 individual fractions (300 per site per method) were randomly selected and the pre-CBCT 3D corrections were calculated and recorded. For both positioning methods, four common treatment site combinations were evaluated: pelvis/lower extremities, abdomen, chest/upper extremities and breast. Statistical differences were evaluated using a paired sample Wilcoxon signed rank test with significance level of <0.01.

Results: The average magnitude of the 3D shift vectors for tattoos were 0.9±0.4 cm, 1.0±0.5cm, 0.9±0.4 cm and 1.1±0.5 cm for the pelvis/lower extremities, abdomen, chest/upper extremities and breast, respectively. For the CatalystHD, the average magnitude of the 3D shifts for the pelvis/lower extremities, abdomen, chest/upper extremities and breast were 0.6±0.3 cm, 0.6±0.3 cm, 0.5±0.2 cm and 0.6±0.2 cm, respectively. Statistically significant differences (p<0.01) in the 3D shift vectors were found for all four sites.

Conclusion: This study shows that the overall 3D shift corrections for patients’ whose initial setup positioning used the C-RAD CatalystHD were smaller with respect to patients’ setup with subdermal tattoos. Surface imaging systems should be considered a viable option to improve initial patient setup.

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