Program Information
Commissioning of Radiofrequency Tracking for Gated SBRT of the Liver Using Novel Motion System
J James*, A Cetnar , V Nguyen , B Wang , University of Louisville, Louisville, KY
Presentations
MO-FG-CAMPUS-J-12 (Monday, July 13, 2015) 5:30 PM - 6:00 PM Room: Exhibit Hall
Purpose: Tracking soft tissue targets has recently been approved as a new application of the Calypso radiofrequency tracking system allowing for gated treatment of the liver based on the motion of the target volume itself. As part of the commissioning process, an end-to-end test was performed using a 3D diode array and 6D motion platform to verify the dosimetric accuracy and establish the workflow of gated SBRT treatment of the liver using Calypso.
Methods: A 4DCT scan of the ScandiDos Delta4 phantom was acquired using the HexaMotion motion platform to simulate realistic breathing motion. A VMAT plan was optimized on the end of expiration phase of the 4DCT scan and delivered to the Delta4 phantom using the Varian TrueBeam. The treatment beam was gated by Calypso to deliver dose at the end of expiration. The expected dose was compared to the delivered dose using gamma analysis. In addition, gating limits were investigated to determine how large the gating range can be while still maintaining dosimetric accuracy.
Results: The 3%/3mm and 2%/2mm gamma pass rate for the gated treatment delivery was 99.9% and 98.3%, respectively. When increasing the gating limits beyond the known extent of planned motion from the 4DCT, the gamma pass rates decreased as expected. The 2%/2mm gamma pass rate for a 1, 2, and 3mm increase in gating limits were measured to be 97.8%, 82.9%, and 61.4 %, respectively.
Conclusion: Radiofrequency tracking was shown to be an effective way to provide gated SBRT treatment of the liver. Baseline gating limits should be determined by measuring the extent of target motion during the respiratory phases used for planning. We recommend adding 1mm to the baseline limits to provide the proper balance between treatment efficiency and dosimetric accuracy.
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