SU‐E‐T‐226: SRT/SBRT Patient Specific QA with a New High Resolution 2D Detector Array

Abstract

Purpose: To evaluate the performance of a new commercially available device for patient specific SBRT pretreatment QA.Materials and Methods: The PTW OCTAVIUS1000SRS was used in this study for patient specific QA measurements for patient undergoing SBRT treatments. Forty five (n=45) individual field and five (n=5) composite plans were measured. All plans were optimized and calculated using Eclipse v8.9. All measurements were performed with the gantry static at the upright orientation. The detector array was placed inside the PTW Octavius II phantom and the source to detector plane distance was set to 100cm. The gamma index was the metric of choice in order to quantify the agreement between measurements and calculations. The tolerance criteria used for the evaluation were 3% dose difference and 3mm distance to agreement and also 2%/2mm. Results: The results of the comparison using 3%/3mm were inconclusive. The number of detectors included in the comparison and the rather loose criteria used caused most comparisons to yield a gamma index of 100%. Comparing the measured and calculated planar dose distributions using 2%/2mm as gamma index tolerances, the average gamma index was 95.9% (min:90.9, max:99.2%). The agreement was also reflected while comparing profiles and isodose distributions. Conclusion: The new PTW Octavius 1000SRS device is able to provide a reliable solution for the patient specific QA of SBRT and SRS plans where small fields are commonly used. Project was partially funded by PTW, NY