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Clinical Experience with Monitoring Frequency of Intra-Fraction Patient Motion Using the ExacTrac System for SRS Treatments

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B Lewis

B Lewis*, W Snyder , G Hugo , S Kim , T Kim , Virginia Commonwealth University, Richmond, VA


TH-EF-605-12 (Thursday, August 3, 2017) 1:00 PM - 3:00 PM Room: 605

Purpose: To investigate the necessity and frequency of online image guidance of stereotactic radiosurgery (SRS) using a thermoplastic immobilization mask with infrared fiducial markers and ExacTrac x-ray guidance. The current protocol utilizes three position verification images throughout the treatment (pretreatment, 1st and 2nd mid-SRS treatments).

Methods: Kilovoltage image-guided setup (Brainlab ExacTrac) data of 104 SRS patients were retrospectively analyzed. Each patient was imaged pretreatment, and at two time points during treatment (1st and 2nd mid-treatment), and bony anatomy of the skull was used to establish setup error at each time point. The datasets included the translational and rotational setup error, as well as the time period between image acquisition. After each image acquisition, the patient was repositioned using the calculated shift to correct the setup error. Only translational errors were corrected. Set up time and directional shift values were analyzed to determine correlation between shift magnitudes as well as time between acquisitions.

Results: The average magnitude shift was 0.64±0.59 mm, 0.79±0.45 mm, and 0.65±0.35 mm for the pre-treatment, 1st mid-treatment, and 2nd mid-treatment imaging time points. The average time from pre-treatment image acquisition to 1st mid-treatment image acquisition was 7.98±0.45 minutes, from 1st to 2nd mid-treatment image was 4.87±1.96 minutes, and the time from pre-treatment image acquisition to 2nd mid-treatment image acquisition was 12.84±3.37 minutes. No patient had a 2nd mid-treatment image with greater than 2mm magnitude shifts.

Conclusion: There was no correlation between patient motion over time, in direction or magnitude, and duration of treatment. The imaging frequency could be reduced to decrease imaging dose and treatment time without significant changes in patient position

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