Click here to


Are you sure ?

Yes, do it No, cancel

Comparing the Accuracy of AlignRT and ExacTrac at Intrafractional Time Points During Cranial Stereotactic Radiosurgery and Stereotactic Radiotherapy Treatments

T Wolken*, S Junell , Oregon Health & Science Univ, Portland, OR


(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: To compare the positioning accuracy of AlignRT (Vision RT, London, UK) and ExacTrac (BrainLAB AG, Feldkirchen, Germany) at intrafractional time points during cranial stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT) treatments.

Methods: Cranial SRS/SRT patients are monitored during treatment with the AlignRT and ExacTrac systems. After initially positioning the patient at table angle zero using ExacTrac x-ray imaging, a baseline ExacTrac image is acquired and the AlignRT system is zeroed out. Mid-treatment and end of treatment ExacTrac images are acquired with the table at baseline position. Using the ExacTrac time stamp as reference, the corresponding AlignRT position information is extracted from the “Real Time Delta� files. The shift from baseline determined by each systems is used to find the relative difference in position between ExacTrac and AlignRT. A phantom study is used to quantify the statistical variations of both systems. Relevant patient anatomy such as cheek dermis thickness was recorded from the patient CT scans in an effort to correlate system accuracy with patient variables.

Results: 58 treatment checks were recorded. The average magnitude of the translational disagreement between AlignRT and ExacTrac was 0.69 millimeters with a standard deviation of 0.28 millimeters. The maximum translational disagreement was 1.54 millimeters. Correlation between cheek dermis thickness and translational disagreement between the two systems was observed (p=0.01). The phantom study determined that the statistical variation of both systems was below 0.1 millimeters.

Conclusion: Agreement between AlignRT and ExacTrac for intrafraction motion detection was sub-millimeter on average with a maximum disagreement of 1.54 millimeters. Correlation between patient anatomy and system disagreement was observed and will be further investigated by increasing the number of unique patients in the study.


Optical Imaging, Planar Imaging, Stereotactic Radiosurgery


IM/TH- Image-guided surgery: General (most aspects)

Contact Email