Accuracy of Dose Delivery in Multiple Breath-Hold Segmented Volumetric Modulated Arc Therapy: A Static Phantom Study

Purpose. Accuracy of dose delivery in multiple breath-hold segmented volumetric modulated arc therapy (VMAT) was evaluated in comparison to noninterrupted VMAT using a static phantom. Material and Methods. Five VMAT plans were evaluated. A Synergy linear accelerator (Elekta AB, Stockholm, Sweden) was employed. A VMAT delivery sequence was divided into multiple segments according to each of the predefined breath-hold periods (10, 15, 20, 30, and 40 seconds). The segmented VMAT delivery was compared to noninterrupted VMAT delivery in terms of the isocenter dose and pass rates of a dose difference of 1% with a dose threshold of 10% of the maximum dose on a central coronal plane using a two-dimensional dosimeter, MatriXX Evolution (IBA Dosimetry, Schwarzenbruck, Germany). Results. Means of the isocenter dose differences were 0.5%, 0.2%, 0.2%, 0.0%, and 0.0% for the beam-on-times between interrupts of 10, 15, 20, 30, and 40 seconds, respectively. Means of the pass rates were 85%, 99.9%, 100%, 100%, and 100% in the same order as the above. Conclusion. Our static phantom study indicated that the multiple breath-hold segmented VMAT maintains stable and accurate dose delivery when the beam-on-time between interrupts is 15 seconds or greater. 1. Introduction Although radiotherapy has been successfully applied to lung, liver, and pancreas tumors [1–3], breathing motion needs to be considered for the tumors located in proximity to the diaphragm [4–9]. A traditional approach is an enlarged internal margin that was added to a gross tumor volume (GTV) or a clinical target volume (CTV), resulting in possible higher complication to neighboring organs at risk (OARs) [10]. To minimize the internal margin, breath-hold with active breathing control (ABC) or patient voluntary breath-hold was used for intensity modulated radiation therapy (IMRT) [4, 10–12] among other techniques such as gating. IMRT provides more conformal dose for the target and more reduced dose for OARs compared to 3D conformal radiotherapy (3D-CRT). A disadvantage of IMRT is increased monitor units and thus beam-on-time, thereby possibly causing larger intrafractional tumor localization error [13, 14]. Volumetric modulated arc therapy (VMAT) allows a faster dose delivery while gantry and multileaf collimator (MLC) are dynamically controlled [15–19]. A combination of breath-hold and VMAT may lead to a quick and accurate treatment option for a moving tumor close to diaphragm. Nevertheless, the beam-on-time for a VMAT delivery is typically two to four minutes, thereby preventing a single breath-hold