Design and Fabrication of a Four-Dimensional Respiratory Phantom for Studying Tumor Movement in Radiotherapy with Magnetic Resonance Imaging

Introduction: In radiation therapy, determining the location of the tumor accurately during irradiation is one of the most important requirements. However, lung tumors are not fixed in a single location and move during irradiation due to respiratory motion. Due to limitations in assessing such movements, using a lung phantom can be useful and operational for their fast, easy and inexpensive assessment. Moreover, Magnetic Resonance Imaging (MRI)- guided radiation therapy is an emerging modality and research is needed increasingly in this field. An advanced aspect of MRI-guidance is its use in respiratory-correlated radiation therapy. To facilitate research on this topic, the aim of this study was to design and build a four-dimensional (4D) respiratory phantom for studying tumor movements in lung radiation therapy. Materials and Methods: By molding a normal human lung, an artificial lung made of silicon was constructed. The chest was made of plexiglas and a double-walled container. The wall was filled with water to increase the MR signal strength. A 1.5-liter thin bag of silicon was made as a synthetic diaphragm and was placed into the chest. Seven tumors were embedded in different parts of the lung. A piston pump was used to simulate the breathing and an engine and gearbox were used to create the reciprocating motion. Results: The phantom is MRI compatible, unlike many of the previously designed 4D lung phantoms. Inspecting the MRI, CT and fluoroscopy x-ray scans taken of the phantom, useful information could be derived from the images which could be applied to simulating and examining the motion and the types of movement of lung tumors. Conclusion: The constructed lung phantom can be a useful tool for research into respiratory- correlated radiation therapy and its new techniques, as well as quality assurance of a variety of 4D imaging devices and protocols.