A novel anthropomorphic multimodality phantom for MRI‐based radiotherapy quality assurance testing

Abstract

Purpose: Increased utilization of magnetic resonance imaging (MRI) in radiotherapy has caused a growing need for phantoms that provide tissue-like contrast in both computed tomography (CT) and MRI images. Such phantoms can be used to compare MRI-based processes with CT-based clinical standards. Here, we develop and demonstrate the clinical utility of a three-dimensional (3D)-printed anthropomorphic pelvis phantom containing materials capable of T 1 , T 2 , and electron density matching for a clinically relevant set of soft tissues and bone. Methods: The phantom design was based on a male pelvic anatomy template with thin boundaries separating tissue types. Slots were included to allow insertion of various dosimeters. The phantom structure was created using a 3D printer. The tissue compartments were filled with carrageenan-based materials designed to match the T 1 and T 2 relaxation times and electron densities of the corresponding tissues. CT and MRI images of the phantom were acquired and used to compare phantom T 1 and T 2 relaxation times and electron densities to literature-reported values for human tissue. To demonstrate clinical utility, the phantom was used for end-to-end testing of an MRI-only treatment simulation and planning workflow. Based on a T 2 -weighted MRI image, synthetic CT (sCT) images were created using a statistical decomposition algorithm (MRIPlanner, Spectronic Research AB, Sweden) and used for dose calculation of volumetric-modulated arc therapy (VMAT) and seven-field intensity-modulated radiation therapy (IMRT) prostate plans. The plans were delivered on a Truebeam STX (Varian Medical Systems, Palo Alto, CA), with film and a 0.3 cc ion chamber used to measure the delivered dose. Doses calculated on the CT and sCTs were compared using common dose volume histogram metrics. Results: T 1 and T 2 relaxation time and electron density measurements for the muscle, prostate, and bone agreed well with literature-reported in vivo measurements. Film analysis resulted in a 99.7% gamma pass rate (3.0%, 3.0 mm) for both plans. The ion chamber-measured dose discrepancies at the isocenter were 0.36% and 1.67% for the IMRT and VMAT plans, respectively. The differences in PTV D98% and D95% between plans calculated on the CT and 1.5T/3.0 T-derived sCT images were under 3%. Conclusion: The developed phantom provides tissue-like contrast on MRI and CT and can be used to validate MRI-based processes through comparison with standard CT-based processes.

A customizable anthropomorphic phantom for dosimetric verification of 3D‐printed lung, tissue, and bone density materials

“…More complex lung scenarios are to be investigated to systematically study behaviors of different deformable image registration algorithms, potentially beneficial for future clinical trial audits utilizing similar advanced imaging tools for multi‐modality target delineation and deformable dose accumulation 15,17,41,42 . This application can be extended toward the 3D printing of realistic phantoms with a mixture of solid and deformable walls, filled with deformable carrageenan‐based materials for the enhanced physical emulation of organ deformation 20 . Different tissue type inserts can be made within an anthropomorphic setting to validate dual‐energy CT contrast resolution of the various tissue types, which is important for particle therapy dose calculation modeling as mapping the stopping power ratio for different tissue types is one of the key sources in beam range uncertainty.…”

“…At present, MEX printing techniques to manufacture a phantom commonly use the indirect manufacturing process, which utilizes 3D printing materials combined with tissue substitutes. In contrast, the direct manufacturing process only uses 3D printing materials 16,18,20 . The indirect manufacturing process uses specialized materials, leading to an increase in material and manufacturing costs—the required manual process for producing the tissue substitute if a specific density range is preferred, often limited to emulating a narrow range of tissue densities, and the use of standard MEX printing parameters inhibiting the accurate replication of internal tissue geometries.…”

“…At present, MEX printing techniques to manufacture a phantom commonly use the indirect manufacturing process, which utilizes 3D printing materials combined with tissue substitutes.In contrast,the direct manufacturing process only uses 3D printing materials. 16,18,20 The indirect manufacturing process uses specialized materials, leading to an increase in material and manufacturing costs-the required manual process for producing the tissue substitute if a specific density range is preferred, often limited to emulating a narrow range of tissue densities, and the use of standard MEX printing parameters inhibiting the accurate replication of internal tissue geometries. In response to these challenges, this work integrates and implements the reported 3D printing techniques utilizing the direct AM process to emulate different tissue densities for lung, soft tissue, and bone 21,22 and establish a proof -of -concept for 3D-printed customizable phantoms for dosimetric verification studies.…”

Deep learning based synthetic‐CT generation in radiotherapy and PET: A review

“…It could be pretty interesting to have a phantom to allow regular QA procedures, for example, for CT. 213 This would be relatively straightforward for II; however, in MR-based sCT, phantoms' manufacturing is quite chal-lenging due to the need for contrast in MRI and CT. Recently, the first phantoms have been proposed for such task [214][215][216][217] showing the potential of additive manufacturing.…”

Deep learning-based synthetic-CT generation in radiotherapy and PET: a review

“…This would be relatively straightforward for II; however, in MR-based sCT, the manufacturing of phantoms is quite challenging due the need of contrast in both MRI and CT images. Recently, the first phantoms have been proposed for such task 180,181,182,183 showing the potential of additive manufacturing.…”