MRIgRT dynamic lung motion thorax anthropomorphic QA phantom: Design, development, reproducibility, and feasibility study

• Published in: Medical physics (Lancaster) 2019-11, Vol.46 (11), p.5124-5133
• Main Authors: Steinmann, A., Alvarez, P., Lee, H., Court, L., Stafford, R., Sawakuchi, G., Wen, Z., Fuller, C., Followill, D.
• Format: Article
• Language: English
• Subjects: end-to-end QA phantom; Feasibility Studies; Humans; Lung - diagnostic imaging; Magnetic Resonance Imaging; MR Linac; MR/CT phantom; MRgRT phantom; MRIgRT phantom; Phantoms, Imaging; Quality Control; Radiometry; Radiotherapy, Image-Guided - instrumentation; Reproducibility of Results; Thorax - diagnostic imaging; Tomography, X-Ray Computed
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1002/mp.13757

Purpose To design, manufacture, and evaluate a dynamic magnetic resonance imaging/computed tomography (MRI/CT)‐compatible anthropomorphic thorax phantom used to credential MR image‐guided radiotherapy (MRIgRT) systems participating in NCI‐sponsored clinical trials. Method The dynamic anthropomorphic thorax phantom was constructed from a water‐fillable acrylic shell that contained several internal structures representing radiation‐sensitive organs within the thoracic region. A custom MR/CT visible cylindrical insert was designed to simulate the left lung with a centrally located tumor target. The surrounding lung tissue was constructed from a heterogeneous in‐house mixture using petroleum jelly and miniature (2–4 mm diameter) styrofoam balls and the tumor structure was manufactured from liquid PVC plastic. An MR conditional pneumatic system was developed to allow the MRIgRT insert to move in similar inhale/exhale motions. TLDs and radiochromic EBT3 film were inserted into the phantom to measure absolute point doses and dose distributions, respectively. The dynamic MRIgRT thorax phantom was evaluated through a reproducibility study and a feasibility study. Comprehensive end‐to‐end examinations were done where the phantom was imaged on a CT, an IMRT treatment plan was created and an MR image was captured to verify treatment setup. Then, the phantom was treated on an MRIgRT system. The reproducibility study evaluated how well the phantom could be reproduced in an MRIgRT system by irradiating three times on an Elekta’s 1.5 T Unity system. The phantom was shipped to three independent institutions and was irradiated on either an MRIdian cobalt‐60 (60Co) or an MRIdian linear accelerator system. Treatment evaluations used TLDs and radiochromic film to compare the planned treatment reported on the treatment planning software against the measured dose on the dosimeters. Results The phantom on the Unity system had reproducible TLD doses measurements (SD