Encrypted login | home

Program Information

Stereotactic Radiosurgery Patient Setup Corrections According to Couch Angle and Target Location

E Welch

E Welch*, A Yock , Vanderbilt University Medical Center, Nashville, TN


WE-RAM3-GePD-J(A)-5 (Wednesday, August 2, 2017) 10:30 AM - 11:00 AM Room: Joint Imaging-Therapy ePoster Lounge - A

Purpose: To evaluate 6 degree-of-freedom patient setup corrections as a function of couch angle and target location for stereotactic radiosurgery.

Methods: We randomly selected forty-five patients treated between 2014 and 2017 for brain metastases using a Novalis Tx. Digital files recorded during treatment were retrospectively compiled and mined for information regarding patient setup corrections determined with a floor and ceiling mounted orthogonal kV x-ray system. This data was combined with additional spatial information of target position determined directly from the treatment planning system. The vector magnitude of the translational correction and the maximum rotational correction were independently analyzed according to couch angle (IEC 61217 coordinates: 270°-330°, 330°-30° inclusive, and 30°-90°) and target location (regions relative to the center of the localizer box). Null hypothesis testing was performed on both translational and rotational corrections using a Wilcoxon rank-sum test to compare the corrections of different couch angles.

Results: The median translational correction for neutral couch angles (330°-30°) was 0.4mm. These corrections were significantly smaller than those for couch angles 270°-330° (0.7mm, p<0.01) and 30°-90° (0.6mm, p<0.01). The spread in correction magnitudes was also considerably less for neutral couch angles. Comparison of the rotational corrections demonstrated an asymmetric dependence on couch angle. These corrections were greater for angles 30°-90°, which was consistent with observations made during periodic QA. Translational corrections were similar in magnitude across target location (range of regional median values: 0.4mm).

Conclusion: In this work, we determined the typical magnitude of translational and rotational patient setup corrections for our stereotactic radiosurgery program. This data incorporates machine-, plan-, and patient-specific information that will assist clinicians and therapists during treatment planning and delivery. It also serves as a basis for cross-institutional comparison of SRS patient setup corrections.

Contact Email: