An abdominal phantom with anthropomorphic organ motion and multimodal imaging contrast for MR-guided radiotherapy

Abstract

Improvements in image-guided-radiotherapy (IGRT) enable accurate and precise radiotherapy treatments of moving tumors in the abdomen while simultaneously sparing healthy tissue. However, the lack of validation tools for newly developed IGRT hybrid devices such as MR-Linac is an open issue. This study presents an abdominal phantom with respiratory organ motion and multimodal imaging contrast to perform end-to-end tests in IGRT. The abdominal phantom contains anatomically shaped liver and kidney models made of Ni-DTPA and KCl-doped agarose mixtures that can be reproducibly positioned within the phantom. Organ models are wrapped in foil to avoid ion exchange with the surrounding agarose-based fatty tissue and to allow stable imaging contrast. Breathing motion is realized by a diaphragm connected to an actuator that is hydraulically controlled via a programmable logic controller (PLC). With this system, artificial and patient-specific breathing patterns can be carried out. In 1.5 and 3 T magnetic resonance imaging (MRI) and computed tomography (CT) series, diaphragm, liver and kidney motion was measured and compared to the breathing motion of a healthy male volunteer for different breathing amplitudes including shallow, normal and deep breathing. The constructed abdominal phantom demonstrated tissue-equivalent contrast in CT as well as in MRI. T1-weighted (T1w) and T2-weighted (T2w) relaxation times and CT-numbers were 552.9 ms, 48.2 ms and 48.8 HU (liver) and 950.42 ms, 79 ms and 28.2 HU (kidney), respectively. These values were stable for more than one month. Extracted breathing motion from a healthy volunteer revealed a liver to diaphragm motion ratio (LDMR) of 64.4 % and a kidney to diaphragm motion ratio (KDMR) of 30.7 %. Well-comparable values were obtained for the phantom (LDMR: 65.5 %, KDMR: 27.5 %). The abdominal phantom demonstrated anthropomorphic imaging contrast and physiological motion pattern in MRI and CT. This allows for wide use in the validation of IGRT.

Developing a 3D-printing-based method to create anthropomorphic dosimeters for radiotherapy-delivery verification

“…They are usually constructed to imitate the head, thoracic, or abdominal region. They should ideally be compatible with both magnetic resonance (MR) and computed tomography (CT) scanners, be deformable and able to move in a respiratory manner [1][2][3][4][5][6].…”

A phantom to simulate organ motion and its effect on dose distribution in carbon ion therapy for pancreatic cancer

“…Based on the development of a phantom for liver treatment (Weidner et al 2022), PPIeT was constructed out of two 5 l cylindrical polypropylene containers, with a height of 26.0 cm, a wall thickness of 2 mm and a transversal ellipse shape with 29.0 cm major axis and 21.0 cm minor axis. These two containers were interlocked and had a frontal cut-out of (24.0 × 10.5) cm 2 for a flexible abdominal wall.…”

“…Therewith, fixed input displacements including 10 mm, 20 mm and 30 mm were applied. Additionally, sinusoidal breathing motions over time t were used as described by Weidner et al (2022):…”

“…This capability becomes especially relevant when considering scenarios involving the movement of tumors and OARs (Cheung and Sawant 2015, Kim et al 2016, Mann et al 2017, Ehrbar et al 2019. Recently, the development of a phantom for liver treatment made it possible to combine breathing motion of different organs with human equivalent CT and MRI contrast to perform end-to-end studies in MR-Linacs (Weidner et al 2022). Notably, there is a growing emphasis on compatibility with MRI systems, leading to the design of phantoms tailored for optimal performance within these environments.…”

Time-Resolved Plastic Scintillator Dosimetry in Mr Linear Accelerators Without Image Distortion

“…Consequently, MR-Linacs have the potential to improve motion management compared to conventional linear accelerators, with a prospect of reducing margins required for tumor coverage and lowering the dose to organs at risk (Corradini et al, 2019). To exploit this new technology without compromising safety, it is relevant to characterize the advanced treatments by independent dosimetry methods including time resolved dosimetry with simultaneous MR based gating (Weidner et al, 2022). Dosimetry in a magnetic field is challenging as the field influences the secondary electron trajectories due to the Lorentz force (Jelen and Begg, 2019;O'Brien et al, 2017).…”