Room: AAPM ePoster Library
Purpose: Radiation dose delivered to targets located near the upper-abdomen or thorax are significantly affected by respiratory-motion, where relatively large-margins are commonly added to compensate for this motion, limiting radiation-dose-escalation capability. Internal-surrogates of target motion, such as Calypso, are used to overcome this challenge and improve normal-tissue sparing. Calypso consist of implanting a fiducial-marker in the vicinity of the tumor to be track using radiofrequency-waves. Unfortunately, although the manufacture provides a universal quality-assurance (QA) phantom, a QA-phantom specifically for lung-applications are limited, warranting the development of alternative-solutions to fulfil the tests mandated by TG142. Accordingly, our objective was to design and develop a motion-phantom to evaluate Calypso for lung-applications that allows the beacons to move in different directions to better simulate lung-motion.
Methods: Design and development of a Calypso lung QA-phantom was performed using Autodesk Fusion360 and an Ultimaker S5. The design consists of three independent arms where the Calypso® beacons were attached to a central-axis and a pinpoint-chamber with a buildup-cap was incorporated for dosimetric evaluation. A Dobot Magician was programmed to drive the central-axis of the motion-phantom to mimic breathing. After acquiring a four-dimensional-computed-tomography (4DCT) scan of the motion-phantom, the scan was imported into Eclipse to generate a treatment-plan to be delivered on a Varian TrueBeam with Calypso capabilities. Stationary and gated-treatment plans were generated and delivered to determine the dosimetric difference between gated and non-gated treatments. Portal gated-images were acquired to determine the temporal-accuracy by calculating the difference between the expected versus delivered beacon locations with the known speed of the beacons’ motion.
Results: The dosimetric beam output-constancy between the gated and ungated-plans were <1%, while the temporal-accuracy was <100ms, which are within the recommendations stated by TG142.
Conclusion: The robotic QA-phantom designed and developed in this study provides an independent phantom for performing Calypso lung QA.