(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose: To demonstrate the use of a novel, rigid phantom for comprehensive end-to-end verification of adaptive radiotherapy (ART) systems. The phantom is intended to validate the entire ART process and associated subsystems.
Methods: An ART end-to-end phantom was designed and constructed in-house. The phantom is composed of high-density polyethylene slabs containing multiple acrylic and high-density objects related through known differences in size, position, and/or shape. Multiple types of dosimeters (e.g. ion chambers and OSLDs) can be positioned in the center of each object. Additionally, film can be placed between the slabs to measure axial dose distributions. Eight clinical treatment plans were created in the treatment planning system (TPS) for a reference phantom configuration. The plans were delivered on an alternative target configuration, achieved through simple phantom manipulation (e.g. 90° rotation), to replace the original target object with another object simulating a change in anatomy. Lastly, an adapted plan designed for this alternative configuration was created. Each plan was delivered, and ion chamber measurements were taken in the target object.
Results: Measured doses closely matched TPS calculations (1.1±1.3%). The target coverage provided by the reference plans was V(100%)=95%. When delivered on alternative configurations, the coverage of the target fell 19±15%. Radiotherapy plans adapted to these configurations regained the desired coverage (V(100%)=95%).
Conclusion: We have successfully used our in-house phantom to validate the ART process including imaging, contouring, plan optimization, and dose calculation. The phantom’s rigid nature allowed for the precise definition of geometric relationships between anatomic objects that simulate changes in targets and organs at risk, demonstrating the need for treatment plan adaptation. The compatibility of the phantom with multiple types of dosimeters allows for adapted plan delivery verification. Current efforts include refining phantom design, implementing additional dosimeters, and utilizing the phantom on additional ART systems.
Keywords
Phantoms, Validation, Morphology
Taxonomy
TH- External Beam- Photons: adaptive therapy
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