Design, performance characteristics and application examples of a new 4D motion platform.

In this publication, a three-dimensionally movable motion phantom is described and its performance characteristics are evaluated. The intended primary fields of application for the phantom are the quality assurance (QA) of respiratory motion management devices in radiation therapy (RT) like gating or tumour tracking systems, training for clinical use of these techniques, and related 4DRT research. Considering especially the QA aspect, the phantom was designed as a motion platform that can be equipped with an appropriate add-on like standard QA phantoms for dosimetric measurements. The platform is driven by three computer-controlled independent linear motors (motion range: 40×50×50mm in anterior-posterior/superior-inferior/lateral direction; max. velocity: 3.9 m/s; max. acceleration: 10 m/s2), which allow the simulation of normal breathing patterns as well as arbitrary trajectories and anomalous events like coughing or baseline drift. For normal breathing patterns (here: sinusoidal curves with an amplitude of 20mm and a period of 3s/6s), the accuracy of the simulated motion paths was measured to be within 0,521mm even for the ArcCHECK® (weight: 20kg) as a platform load – values that we consider to be sufficient for the intended fields of application. The respective use of the motion phantom is illustrated.