SU‐C‐BRD‐04: Comparison of Shallow Fluence to Deep Point Dose Measurements for Spine VMAT SBRT Patient‐Specific QA

TL;DRAbstract

Purpose: To investigate the sensitivity of traditional gamma‐index‐based fluence measurements for patient‐specific measurements in VMAT delivered spine SBRT. Methods: The ten most recent cases for spine SBRT were selected. All cases were planned with Eclipse RapidArc for a TrueBeam STx. The delivery was verified using a point dose measurement with a Pinpoint 3D micro‐ion chamber in a Standard Imaging Stereotactic Dose Verification Phantom. Two points were selected for each case, one within the target in a low dose‐gradient region and one in the spinal cord. Measurements were localized using on‐board CBCT. Cumulative and separate arc measurements were acquired with the ArcCheck and assessed using the SNC patient software with a 3%/3mm and 2%/2mm gamma analysis with global normalization and a 10% dose threshold. Correlations between data were determined using the Pearson Product‐Moment Correlation. Results: For our cohort of patients, the measured doses were higher than calculated rangin

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