skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Technical note: A deformable phantom for dynamic modeling in radiation therapy

Abstract

A deformable phantom was developed to aid in quality assurance for dynamic imaging and targeting techniques in radiation therapy. Made of simple materials combined with standard components for imaging and motion experiments, this phantom can be relatively easily constructed and used for both diagnostic imaging and dosimetry. Repeat imaging studies indicate that the phantom meets criteria of relative attenuation, deformation, and reproducibility of configuration, necessary for quality assurance of radiographic and tomographic targeting.

Authors:
; ; ;  [1]
  1. Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan 48109 (United States)
Publication Date:
OSTI Identifier:
20853910
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 34; Journal Issue: 1; Other Information: DOI: 10.1118/1.2400612; (c) 2007 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
61 RADIATION PROTECTION AND DOSIMETRY; COMPUTERIZED TOMOGRAPHY; DEFORMATION; DOSIMETRY; PHANTOMS; QUALITY ASSURANCE; RADIOTHERAPY; SIMULATION

Citation Formats

Kashani, Rojano, Lam, Kwok, Litzenberg, Dale, and Balter, James. Technical note: A deformable phantom for dynamic modeling in radiation therapy. United States: N. p., 2007. Web. doi:10.1118/1.2400612.
Kashani, Rojano, Lam, Kwok, Litzenberg, Dale, & Balter, James. Technical note: A deformable phantom for dynamic modeling in radiation therapy. United States. doi:10.1118/1.2400612.
Kashani, Rojano, Lam, Kwok, Litzenberg, Dale, and Balter, James. Mon . "Technical note: A deformable phantom for dynamic modeling in radiation therapy". United States. doi:10.1118/1.2400612.
@article{osti_20853910,
title = {Technical note: A deformable phantom for dynamic modeling in radiation therapy},
author = {Kashani, Rojano and Lam, Kwok and Litzenberg, Dale and Balter, James},
abstractNote = {A deformable phantom was developed to aid in quality assurance for dynamic imaging and targeting techniques in radiation therapy. Made of simple materials combined with standard components for imaging and motion experiments, this phantom can be relatively easily constructed and used for both diagnostic imaging and dosimetry. Repeat imaging studies indicate that the phantom meets criteria of relative attenuation, deformation, and reproducibility of configuration, necessary for quality assurance of radiographic and tomographic targeting.},
doi = {10.1118/1.2400612},
journal = {Medical Physics},
number = 1,
volume = 34,
place = {United States},
year = {Mon Jan 15 00:00:00 EST 2007},
month = {Mon Jan 15 00:00:00 EST 2007}
}
  • Purpose: A novel 4D in vivo dosimetry system (RADPOS), in conjunction with a deformable lung phantom, has been evaluated as a potential quality assurance tool for 4D radiotherapy. Methods: RADPOS detectors, which consist of a MOSFET dosimeter combined with an electromagnetic positioning probe, were placed inside the deformable lung phantom. One detector was positioned directly inside a tumor embedded in the lung phantom and another was positioned inside the lung portion of the phantom, outside the tumor. CT scans were taken with the phantom at three breathing phases, and for each phase, the detector position inside the phantom was readmore » with the RADPOS software and compared to the position as determined from the CT data. These values were also compared to RADPOS measurements taken with the phantom on the couch of a Varian Clinac 6EX linac. The deformable phantom and the RADPOS system were also used in two radiation delivery scenarios: (1) A simulation of a free-breathing delivery and (2) a simulation of an adaptive treatment. Results: Compared to CT imaging, the RADPOS positional accuracy was found to be better than 2.5 mm. The radial displacement measurements taken in the CT and linac rooms agreed to within an average of (0.7{+-}0.3) mm. Hence, the system can provide relative displacement measurements in the treatment room, consistent with measurements made in the CT room. For the free-breathing delivery, the total dose reported by RADPOS agreed to within 4% and 5% of the treatment planning doses in the tumor and the lung portion of the phantom, respectively. The RADPOS-measured dose values for the adaptive delivery were within 1.5% of the treatment plan values, which was well within the estimated experimental uncertainties. Conclusions: This work has shown that the deformable lung phantom-RADPOS system can be an efficient quality assurance tool for 4D radiation therapy.« less
  • Purpose: Dynamic tumor tracking radiation therapy can potentially reduce internal margin without prolongation of irradiation time. However, dynamic tumor tracking technique requires an extra margin (tracking margin, TM) for the uncertainty of tumor localization, prediction, and beam repositioning. The purpose of this study was to evaluate a dosimetric impact caused by TM. Methods: We used 4D XCAT to create 9 digital phantom datasets of different tumor size and motion range: tumor diameter TD=(1, 3, 5) cm and motion range MR=(1, 2, 3) cm. For each dataset, respiratory gating (30%–70% phase) and tumor tracking treatment plans were created using 8-field 3D-CRTmore » by 4D dose calculation implemented in RayStation. The dose constraint was based on RTOG0618. For the tracking plan, TMs of (0, 2.5, 5) mm were considered by surrounding a normal setup margin: SM=5 mm. We calculated V20 of normal lung to evaluate the dosimetric impact for each case, and estimated an equivalent TM that affects the same impact on V20 obtained by the gated plan. Results: The equivalent TMs for (TD=1 cm, MR=2 cm), (TD=1 cm, MR=3 cm), (TD=5 cm, MR=2 cm), and (TD=5 cm, MR=3 cm) were estimated as 1.47 mm, 3.95 mm, 1.04 mm, and 2.13 mm, respectively. The larger the tumor size, the equivalent TM became smaller. On the other hand, the larger the motion range, the equivalent TM was found to be increased. Conclusion: Our results showed the equivalent TM changes depending on tumor size and motion range. The tracking plan with TM less than the equivalent TM achieves a dosimetric impact better than the gated plan in less treatment time. This study was partially supported by JSPS Kakenhi and Varian Medical Systems.« less
  • The purpose of this study was to investigate the feasibility of a simple deformable phantom as a QA tool for testing and validation of deformable image registration algorithms. A diagnostic thoracic imaging phantom with a deformable foam insert was used in this study. Small plastic markers were distributed through the foam to create a lattice with a measurable deformation as the ground truth data for all comparisons. The foam was compressed in the superior-inferior direction using a one-dimensional drive stage pushing a flat 'diaphragm' to create deformations similar to those from inhale and exhale states. Images were acquired at differentmore » compressions of the foam and the location of every marker was manually identified on each image volume to establish a known deformation field with a known accuracy. The markers were removed digitally from corresponding images prior to registration. Different image registration algorithms were tested using this method. Repeat measurement of marker positions showed an accuracy of better than 1 mm in identification of the reference marks. Testing the method on several image registration algorithms showed that the system is capable of evaluating errors quantitatively. This phantom is able to quantitatively assess the accuracy of deformable image registration, using a measure of accuracy that is independent of the signals that drive the deformation parameters.« less
  • Purpose: Phantom surrogates were developed to allow multimodal [computed tomography (CT), magnetic resonance imaging (MRI), and teletherapy] and anthropomorphic tissue simulation as well as materials and methods to construct deformable organ shapes and anthropomorphic bone models. Methods: Agarose gels of variable concentrations and loadings were investigated to simulate various soft tissue types. Oils, fats, and Vaseline were investigated as surrogates for adipose tissue and bone marrow. Anthropomorphic shapes of bone and organs were realized using 3D-printing techniques based on segmentations of patient CT-scans. All materials were characterized in dual energy CT and MRI to adapt CT numbers, electron density, effectivemore » atomic number, as well as T1- and T2-relaxation times to patient and literature values. Results: Soft tissue simulation could be achieved with agarose gels in combination with a gadolinium-based contrast agent and NaF to simulate muscle, prostate, and tumor tissues. Vegetable oils were shown to be a good representation for adipose tissue in all modalities. Inner bone was realized using a mixture of Vaseline and K{sub 2}HPO{sub 4}, resulting in both a fatty bone marrow signal in MRI and inhomogeneous areas of low and high attenuation in CT. The high attenuation of outer bone was additionally adapted by applying gypsum bandages to the 3D-printed hollow bone case with values up to 1200 HU. Deformable hollow organs were manufactured using silicone. Signal loss in the MR images based on the conductivity of the gels needs to be further investigated. Conclusions: The presented surrogates and techniques allow the customized construction of multimodality, anthropomorphic, and deformable phantoms as exemplarily shown for a pelvic phantom, which is intended to study adaptive treatment scenarios in MR-guided radiation therapy.« less
  • Purpose: MRI has become an attractive tool for tumor motion management. Current MR-compatible phantoms are only capable of reproducing translational motion. This study describes the construction and validation of a more realistic, MRI-compatible lung phantom that is deformable internally as well as externally. We demonstrate a radiotherapy application of this phantom by validating the geometric accuracy of the open-source deformable image registration software NiftyReg (UCL, UK). Methods: The outer shell of a commercially-available dynamic breathing torso phantom was filled with natural latex foam with eleven water tubes. A rigid foam cut-out served as the diaphragm. A high-precision programmable, in-house, MRI-compatiblemore » motion platform was used to drive the diaphragm. The phantom was imaged on a 3T scanner (Philips, Ingenia). Twenty seven tumor traces previously recorded from lung cancer patients were programmed into the phantom and 2D+t image sequences were acquired using a sparse-sampling sequence k-t BLAST (accn=3, resolution=0.66×0.66×5mm3; acquisition-time=110ms/slice). The geometric fidelity of the MRI-derived trajectories was validated against those obtained via fluoroscopy using the on board kV imager on a Truebeam linac. NiftyReg was used to perform frame by frame deformable image registration. The location of each marker predicted by using NiftyReg was compared with the values calculated by intensity-based segmentation on each frame. Results: In all cases, MR trajectories were within 1 mm of corresponding fluoroscopy trajectories. RMSE between centroid positions obtained from segmentation with those obtained by NiftyReg varies from 0.1 to 0.21 mm in the SI direction and 0.08 to 0.13 mm in the LR direction showing the high accuracy of deformable registration. Conclusion: We have successfully designed and demonstrated a phantom that can accurately reproduce deformable motion under a variety of imaging modalities including MRI, CT and x-ray fluodoscopy, making it an invaluable research tool for validating novel motion management strategies. This work was partially supported through research funding from National Institutes of Health (R01CA169102).« less