RADT-47. MARGIN REDUCTION WITH THE INTRODUCTION OF INTRA-FRACTIONAL MONITORING USING IDENTIFY SGRT FOR FRAMELESS STEREOTACTIC CRANIAL RADIOSURGERY (SRS)

Abstract

Abstract The purpose of this study was to evaluate the potential for margin reduction in clinical treatment settings based on the accuracy of Varian Identify SGRT (Surface-Guided Radiation Therapy). The study considered various factors such as patient setup variations, intrafraction movement, and unique facial features. Identify version 2.3.1 was installed on a Truebeam v2.7 system and commissioned according to AAPM TG3021 test recommendations. Identify generated reports on patient offsets in all six degrees of freedom during motion monitoring. These offsets were retrospectively compared with radiographic images (CBCT and MV planar images) to determine the accuracy of patient positioning achieved using surface guidance. A retrospective analysis of 36 patients was performed for a total of 125 fractions. The characteristics of the patient cohort (age range from 39 – 92 years) consisted of a mixture of 8 benign, 28 malignant lesions, 11 single, 25 standard fully-fractionated treatments and anatomical sites such as parietal, frontal, ventricle, base of skull, pons and acoustic neuromas. RESULTS: show that for this clinical cohort, the variance between Identify and radiographic imaging ranges from -0.02 to 0.08 cm, -0.09 to 0.10 cm, -0.09 to 0.09 cm and -0.81 to 0.74 degrees for the vertical, longitudinal, lateral and rotation respectively. This average variance in the translational axes is 0.0cm ± 0.0014 cm, indicating no directional preference. The 3D vector of the displacement detected achievable by Identify is 1 mm within a 95% confidence interval (CI). Based on the findings, the researchers concluded that a minimum GTV-PTV (Gross Tumor Volume-Planning Target Volume) margin of 1 mm is appropriate for intrafraction monitoring with Identify SGRT on the TrueBeam system for stereotactic cranial treatments. This information can increase the radiation oncologist's confidence in patient positioning during treatment delivery and potentially lead to a decrease in the GTV-PTV margin.