3D dosimetric validation of motion compensation concepts in radiotherapy using an anthropomorphic dynamic lung phantom

Mann, P.; Witte, Maximilian; Moser, T.; Lang, Clemens; Runz, A.; Johnen, W.; Berger, M.; Biederer, J.; Karger, Christian P.

doi:10.1088/1361-6560/aa51b1

Cited by 40 publications

(51 citation statements)

References 48 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Secondly, for patient cases, image artifacts caused by different magnetic susceptibility may occur, leading to additional magnetic field distortions of the resulting MR images . Future studies should take these effects into account by combination of measurements with both rigid phantoms having highly reproducible motion behaviors and dynamic nonrigid anthropomorphic phantoms . Lastly, since in this study the phantom was tested on a diagnostic MR system, the validation of motion accuracy and geometric fidelity in an MRgRT environment would still be necessary.…”

Section: Discussionmentioning

confidence: 99%

Commissioning of a 4D MRI phantom for use in MR‐guided radiotherapy

et al. 2018

View full text Add to dashboard Cite

Purpose: Systems for integrated magnetic resonance guided radiation therapy (MRgRT) provide real-time and online MRI guidance for unequaled targeting performance of moving tumors and organs at risk. The clinical introduction of such systems requires dedicated methods for commissioning and routine machine quality assurance (QA). The aim of the study was to develop a commissioning protocol and method for automatic quantification of target motion and geometric accuracy using a 4D MRI motion phantom. Materials and methods: The commissioning was performed on a clinically used 3 T MR scanner. The phantom was positioned on a flat tabletop overlay using an in-house constructed base plate for a quick and reproducible setup. The torso-shaped phantom body, which was filled with mineral oil as signal generating medium, included a 3D grid structure for image distortion analysis and a cylindrical thru-hole in which a software-controlled moving rod with a hypo-intense background gel and a decentralized hyper-intense target simulated 3D organ motion patterns. To allow for sequence optimization, MR relaxometry was performed to determine the longitudinal T 1 and transverse T 2 relaxation times of both target and background gel in the movable cylinder. The geometric image distortion was determined as the mean and maximum 3D Euclidean distance (D mean , D max ) of grid points determined by nonrigid registration of a 3D spoiled gradient echo MRI scan and a CT scan. Sinusoidal 1D/2D/3D motion trajectories, varying in amplitude and frequency, as well as an exemplary 1D MR navigator diaphragm motion pattern extracted from a healthy volunteer scan, were scanned by means of 2D cine MRI and 4D MRI. Target positions were automatically extracted from 2D cine MRI using an in-house developed software tool. Results: The base plate enabled a reproducible setup with a deviation of <1 mm in all directions. Relaxometry yielded T 1 /T 2 values for target and background gel of 208.1 AE 2.8/30.5 AE 4.7 ms and 871 AE 36/13.4 AE 1.3 ms, respectively. The 3D geometric image distortion increased with distance from the magnetic isocenter, with D mean = 0.58 AE 0.30 mm and D max = 1.31 mm. The frequencies of the reconstructed motion patterns agreed with the preset values within 0.5%, whereas the reconstructed amplitudes showed a maximum deviation to the preset amplitudes of <0.5 mm in AP/LR direction and <0.3 mm in IS direction. Conclusion: A method and protocol for commissioning of a 4D MRI motion phantom on a 3 T MR scanner for MRgRT was developed. High-contrast and geometrically reliable 2D cine MR images of the phantom's moving target could be obtained. The preset motion parameters could be extracted with sufficient spatio-temporal accuracy from 2D cine MRI in all motion directions. The overall 3D geometric image distortion of <1.31 mm within the phantom grid confirms geometric accuracy of the clinically utilized 3D spoiled gradient echo sequence. The method developed can be used for routine QA tests of spatio-temporally resolved MRI data in MRgRT.

show abstract

Section: Discussionmentioning

confidence: 99%

Commissioning of a 4D MRI phantom for use in MR‐guided radiotherapy

et al. 2018

View full text Add to dashboard Cite

show abstract

“…Besides, a morphological high‐resolution standard true fast imaging sequence with steady state precession (TrueFISP) of the prostate organ model was acquired for later co‐registration of the MRI with the treatment planning CT. The MR images were evaluated using an in‐house written gel dose evaluation tool based on Matlab code (Mathworks Inc, Natick) 24 . The data from the eight calibration vials were used to establish a calibration curve between dose and R2‐relaxation rate.…”

Section: Methodsmentioning

confidence: 99%

“…The MR images were evaluated using an in-house written gel dose evaluation tool based on Matlab code (Mathworks Inc, Natick). 24 The data from the eight calibration vials were used to establish a calibration curve between dose and R2-relaxation rate. For each calibration vial, a circular region of interest was defined to determine the mean R2 value and the related standard deviation on the different images of the MR-acquisition.…”

Section: Dose Evaluationmentioning

confidence: 99%

Technical Note: On the feasibility of performing dosimetry in target and organ at risk using polymer dosimetry gel and thermoluminescence detectors in an anthropomorphic, deformable, and multimodal pelvis phantom

et al. 2021

View full text Add to dashboard Cite

Objective To assess the feasibility of performing dose measurements in the target (prostate) and an adjacent organ at risk (rectum) using polymer dosimetry gel and thermoluminescence detectors (TLDs) in an anthropomorphic, deformable, and multimodal pelvis phantom (ADAM PETer). Methods The 3D printed prostate organ surrogate of the ADAM PETer phantom was filled with polymer dosimetry gel. Nine TLD600 (LiF:Mg,Ti) were installed in 3 × 3 rows on a specifically designed 3D‐printed TLD holder. The TLD holder was inserted into the rectum at the level of the prostate and fixed by a partially inflated endorectal balloon. Computed tomography (CT) images were taken and treatment planning was performed. A prescribed dose of 4.5 Gy was delivered to the planning target volume (PTV). The doses measured by the dosimetry gel in the prostate and the TLDs in the rectum (“measured dose”) were compared to the doses calculated by the treatment planning system (“planned dose”) on a voxel‐by‐voxel basis. Results In the prostate organ surrogate, the 3D‐γ‐index was 97.7% for the 3% dose difference and 3 mm distance to agreement criterium. In the center of the prostate organ surrogate, measured and planned doses showed only minor deviations (<0.1 Gy, corresponding to a percentage error of 2.22%). On the edges of the prostate, slight differences between planned and measured doses were detected with a maximum deviation of 0.24 Gy, corresponding to 5.3% of the prescribed dose. The difference between planned and measured doses in the TLDs was on average 0.08 Gy (range: 0.02–0.21 Gy), corresponding to 1.78% of the prescribed dose (range: 0.44%–4.67%). Conclusions The present study demonstrates the feasibility of using polymer dosimetry gel and TLDs for 3D and 1D dose measurements in the prostate and the rectum organ surrogates in an anthropomorphic, deformable and multimodal phantom. The described methodology might offer new perspectives for end‐to‐end tests in image‐guided adaptive radiotherapy workflows.

show abstract

“…Various studies have analyzed the MRI response of polymer gels for possible application in radiotherapy dose mapping ([ 58 , 63 ] and references therein). In particular, polymer gels have been investigated for dosimetry in conformal therapy, IMRT, IMAT, IGRT, VMAT and tomotherapy [ 55 , 70 , 83 , 88 , 102 , 105 , 106 , 107 , 108 , 109 , 110 , 111 , 112 , 113 , 114 , 115 , 116 , 117 , 118 , 119 , 120 , 121 , 122 , 123 , 124 , 125 , 126 , 127 , 128 , 129 , 130 , 131 , 132 , 133 , 134 , 135 ], small photon fields [ 136 , 137 , 138 ], stereotactic radiosurgery [ 55 , 139 , 140 , 141 , 142 ], 60-cobalt source [ 143 , 144 ], brachytherapy [ 55 , 85 , 92 , 145 , ...…”

Section: Polyacrylamide Gelsmentioning

confidence: 99%

Hydrogels for Three-Dimensional Ionizing-Radiation Dosimetry

Marrale

D’Errico

2021

Gels

View full text Add to dashboard Cite

Radiation-sensitive gels are among the most recent and promising developments for radiation therapy (RT) dosimetry. RT dosimetry has the twofold goal of ensuring the quality of the treatment and the radiation protection of the patient. Benchmark dosimetry for acceptance testing and commissioning of RT systems is still based on ionization chambers. However, even the smallest chambers cannot resolve the steep dose gradients of up to 30–50% per mm generated with the most advanced techniques. While a multitude of systems based, e.g., on luminescence, silicon diodes and radiochromic materials have been developed, they do not allow the truly continuous 3D dose measurements offered by radiation-sensitive gels. The gels are tissue equivalent, so they also serve as phantoms, and their response is largely independent of radiation quality and dose rate. Some of them are infused with ferrous sulfate and rely on the radiation-induced oxidation of ferrous ions to ferric ions (Fricke-gels). Other formulations consist of monomers dispersed in a gelatinous medium (Polyacrylamide gels) and rely on radiation-induced polymerization, which creates a stable polymer structure. In both gel types, irradiation causes changes in proton relaxation rates that are proportional to locally absorbed dose and can be imaged using magnetic resonance imaging (MRI). Changes in color and/or opacification of the gels also occur upon irradiation, allowing the use of optical tomography techniques. In this work, we review both Fricke and polyacrylamide gels with emphasis on their chemical and physical properties and on their applications for radiation dosimetry.

show abstract

3D dosimetric validation of motion compensation concepts in radiotherapy using an anthropomorphic dynamic lung phantom

Cited by 40 publications

References 48 publications

Commissioning of a 4D MRI phantom for use in MR‐guided radiotherapy

Commissioning of a 4D MRI phantom for use in MR‐guided radiotherapy

Technical Note: On the feasibility of performing dosimetry in target and organ at risk using polymer dosimetry gel and thermoluminescence detectors in an anthropomorphic, deformable, and multimodal pelvis phantom

Hydrogels for Three-Dimensional Ionizing-Radiation Dosimetry

Contact Info

Product

Resources

About