Author: Hongyu Jiang, Wangyao Li, Dima Soultan, Fen Wang, Jun Xu 👨🔬
Affiliation: Department of Radiation Oncology, University of Kansas Medical Center 🌍
Purpose: To validate the Auto-Beam Hold functionality via the MMI connection between Varian SGRT system IDENTIFY 3.0 and treatment linacs.
Methods: A treatment plan was created in the Eclipse TPS using a simulation CT of the penta-guide cube. The plan consisted of three open AP fields with (200, 500, 999) MUs. A 0.6cc volume was contoured at the center of the cube, at a depth of 8cm, and the calculated dose in this volume was recorded for all three fields. On the treatment machine, a solid water phantom and a Farmer chamber were positioned at the same depth as the treatment plan’s calculation volume. The fields were delivered first without gating. Next, the gating workflow in IDENTIFY was implemented using the RPM block and the associated breathing motion management phantom, and a region of interest ROI for tracking and gating was defined on the RPM block. Four gating scenarios were tested: auto-beam hold alone, auto-beam hold with maximum beam delay [3 sec], auto-beam hold with maximum MU tolerance [5%] , and auto-beam hold with both beam 1 sec delay and 5% MU tolerance. These scenarios combined all features of the auto-beam hold functionality to assess any discrepancies caused by automatically triggering the beam off/on while utilizing these features.
Results: Dose measurements were collected for both the non-gated delivery and the four gating scenarios, and the results were compared to the planned dose. The average discrepancy was ±1.9%, with a maximum observed discrepancy of ±3.6%, which occurred at the lowest MU field and a 3 sec beam delay setting.
Conclusion: The IDENTIFY 3.0 auto-beam hold function, along with its various features relying on surface motion tracking to gate the treatment beam, performed as intended, ensuring safe and effective gated treatment delivery.