Clinical Commissioning of Surface-Guided Manual Gating for Deep Inspiration Breath Hold (Dibh) Breast Radiotherapy on Ethos and Halcyon Systems
Abstract
Purpose
This work commissioned a manual beam gating procedure for breast DIBH treatment on Ethos and Halcyon (O-ring) platforms, which included dosimetric consistency evaluation with an End-to-End (E2E) test and quantifying the response time of manual beam-hold using retrospective logfile analysis.
Methods
Following TG-142 guidance, beam output consistency was evaluated by comparing gated and static deliveries. A surface-guided manual gating procedure was developed and validated through an E2E test using a representative breast VMAT DIBH plan (3 arcs, 520cGy × 5). Respiratory motion was simulated using the QUASAR motion platform with a patient breathing trace. A 2D array detector was placed on the platform (superior-inferior motion), and the associated anterior-posterior motion of a styrofoam surrogate was monitored using AlignRT. During delivery, a radiation therapist (RTT) continuously monitored the AlignRT real-time delta (RTD) and manually held the beam delivery when the gating tolerance (±3mm in translational directions) was exceeded. Dosimetric evaluation was performed by comparing isoplane doses of the reference (static phantom) and gated (moving phantom) deliveries. For timing assessment, RTD timestamps of out-of-tolerance states were compared with beam-hold events from machine log files, with both clocks synchronized within 0.3 seconds.
Results
The difference in beam output between gated and non-gated deliveries was ≤0.1%. The average response time of nine beam-hold interventions was 0.602s [range: 0.179s to 0.905s]. Gamma analysis using 3%/2 mm criteria showed passing rates of 100%, 98.5%, and 98.8% between the gated deliveries compared with the static reference for three fields, respectively.
Conclusion
In the absence of automated beam control on O-ring platforms, commissioning of surface-guided manual gating is necessary. Manually gated DIBH showed dosimetric equivalence to static delivery and sub-second response times, supporting its safety and clinical feasibility for DIBH breast treatments. Careful monitoring of manual beam-holds is required during clinical implementation, particularly for inconsistent breath-hold reproducibility.