Technical note: Optimizing the deliverability of binary collimation-based SRS treatment for multiple metastases with multiple prescriptions

intra-arc binary collimation (iABC) is a novel treatment technique in which dynamic conformal arcs are periodically interrupted with binary collimation. It has demonstrated its utility through planning studies for the treatment of multiple metastases. However, the binary collimation approach is idealized in the planning system, while the treatment deliveries must adhere to the physical limitations of the mechanical systems involved [e.g., multi-leaf collimation (MLC) leaf speed]. This work focuses on optimizing the delivery of the binary collimation-based stereotactic radiosurgery/radiotherapy (SRS/SRT) plans on a Varian TrueBeam accelerator, considering both dosimetric fidelity and treatment efficiency as variables. A transition window (TW) was defined as the fraction of a control point (CP) during which the requested MLC motion must be completed. The width of TWs was varied between 0% (or step-and-shoot which represents the idealized dose distribution), 20%, 40%, 60%, 80%, and 100%. A variable TW approach was also studied. Delivery accuracy was quantified with gamma analysis (gamma criteria 5%/2mm) on a PTW Octavius detector. The total beam-on-time was manually recorded. Smaller TWs were associated with more accurate dose deliveries and longer treatment delivery times. The variable TW method was found to be an effective compromise, achieving an average gamma pass rate of 98% and an average delivery time of 9 min.