Abstract
BackgroundGated Volumetric Modulated Arc Therapy (VMAT) is an emerging radiation therapy modality for treatment of tumors affected by respiratory motion. However, gating significantly prolongs the treatment time, as delivery is only activated during a single respiratory phase. To enhance the efficiency of gated VMAT delivery, a novel dual-gated VMAT (DG-VMAT) technique, in which delivery is executed at both exhale and inhale phases in a given arc rotation, is developed and experimentally evaluated.MethodsArc delivery at two phases is realized by sequentially interleaving control points consisting of MUs, MLC sequences, and angles of VMAT plans generated at the exhale and inhale phases. Dual-gated delivery is initiated when a respiration gating signal enters the exhale window; when the exhale delivery concludes, the beam turns off and the gantry rolls back to the starting position for the inhale window. The process is then repeated until both inhale and exhale arcs are fully delivered. DG-VMAT plan delivery accuracy was assessed using a pinpoint chamber and diode array phantom undergoing programmed motion.ResultsDG-VMAT delivery was experimentally implemented through custom XML scripting in Varian’s TrueBeam™ STx Developer Mode. Relative to single gated delivery at exhale, the treatment time was improved by 95.5% for a sinusoidal breathing pattern. The pinpoint chamber dose measurement agreed with the calculated dose within 0.7%. For the DG-VMAT delivery, 97.5% of the diode array measurements passed the 3%/3 mm gamma criterion.ConclusionsThe feasibility of DG-VMAT delivery scheme has been experimentally demonstrated for the first time. By leveraging the stability and natural pauses that occur at end-inspiration and end-exhalation, DG-VMAT provides a practical method for enhancing gated delivery efficiency by up to a factor of two.
Highlights
Gated Volumetric Modulated Arc Therapy (VMAT) is an emerging radiation therapy modality for treatment of tumors affected by respiratory motion
Improving gated delivery efficiency is of particular importance in Stereotactic Body Radiation Therapy (SBRT), because of the already protracted delivery associated with large dose fractions
The dosimetric variation of dual-gated VMAT (DG-VMAT) versus conventional single gated plans will depend on the patient anatomy on EOE and EOI phases, and the quality of the plans for each phase
Summary
Gated Volumetric Modulated Arc Therapy (VMAT) is an emerging radiation therapy modality for treatment of tumors affected by respiratory motion. While theoretically, continuous tracking delivery has the potential for full duty cycle efficiency [17], due to stringent technical demands, and more importantly, clinical concerns in accurately predicting and irradiating the more variable portions of the breathing cycle in-between the more stable exhale and inhale, its clinical application on a conventional multileaf collimator linac has been limited. For these reasons, a simple and technically practical solution for enhancing gated delivery that irradiates only the clinically reliable portions of the breathing cycle is desirable
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