Use of a megavoltage electronic portal imaging device to identify prosthetic materials

Moutrie, Vaughan; Kairn, Tanya; Rosenfeld, Anatoly B.; Charles, Paul

doi:10.1007/s13246-015-0327-8

Cited by 13 publications

(9 citation statements)

References 22 publications

(27 reference statements)

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“…This becomes more challenging when implementing a dual printing process or when using variable infill densities throughout a phantom. A range of clinical TPSs also require RED for dose calculation but the differences between RED and RED eff are not easy, or often possible, to determine without radiological measurement 13 . A feasible alternate approach during the production of phantoms could be able to generate phantom‐specific CT conversion curves as suggested in Figure 3.…”

Section: Discussionmentioning

confidence: 99%

“…Physical density of the sample objects was determined by measurement, assuming homogeneity. The effective electron density (RED eff ) as described by Moutrie, was derived using the method described by Van der Walt et al using a CC04 chamber 13,14 . Previous works by Tello and Allahverdi have shown plastic water to perform within 0.5% of water for a 6 MV beam, and so no further corrections were applied to convert between plastic and real water thickness 15,16 …”

Section: Methodsmentioning

confidence: 99%

“…The effective electron density (RED eff ) as described by Moutrie, was derived using the method described by Van der Walt et al using a CC04 chamber. 13,14 Previous works by Tello and Allahverdi have shown plastic water to perform within 0.5% of water for a 6 MV beam, and so no further corrections were applied to convert between plastic and real water thickness. 15,16 Following the determination of the RED eff of the 50 × 50 × 50 mm PLA object printed with a 90% infill, the transmission measurements were repeated with each side of the cube directly facing the incident beam.…”

Section: Physical and Radiological Densitymentioning

confidence: 99%

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Investigation of the effects of spinal surgical implants on radiotherapy dosimetry: A study of 3D printed phantoms

et al. 2021

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Purpose The use of three‐dimensional (3D) printing to develop custom phantoms for dosimetric studies in radiotherapy is increasing. The process allows production of phantoms designed to evaluated specific geometries, patients, or patient groups with a defining feature. The ability to print bone‐equivalent phantoms has, however, proved challenging. The purpose of this work was to 3D print a series of three similar spine phantoms containing no surgical implants, implants made of titanium, and implants made of carbon fiber, for future dosimetric and imaging studies. Phantoms were evaluated for (a) tissue and bone equivalence, (b) geometric accuracy compared to design, and (c) similarity to one another. Methods Sample blocks of PLA, HIPS, and StoneFil PLA‐concrete with different infill densities were printed to evaluate tissue and bone equivalence. The samples were used to develop CT to physical (PD) and effective relative electron density (REDeff) conversion curves and define the settings for printing the phantoms. CT scans of the printed phantoms were obtained to assess the geometry and densities achieved. Mean distance to agreement (MDA) and DICE coefficient (DSC) values were calculated between contours defining the different materials, obtained from design and like phantom modules. HU values were used to determine PD and REDeff and subsequently evaluate tissue and bone equivalence. Results Sample objects showed linear relationships between HU and both PD and REDeff for both PLA and StoneFil. The PD and REDeff of the objects calculated using clinical CT conversion curves were not accurate and custom conversion curves were required. PLA printed with 90% infill density was found to have a PD of 1.11 ± 0.03 g.cm−3 and REDeff of 1.04 ± 0.02 and selected for tissue‐ equivalent phantom elements. StoneFil printed with 100% infill density showed a PD of 1.35 ± 0.03 g.cm−3 and REDeff of 1.24 ± 0.04 and was selected for bone‐equivalent elements. Upon evaluation of the final phantoms, the PLA elements displayed PD in the range of 1.10 ± 0.03 g.cm−3–1.13 ± 0.03 g.cm−3 and REDeff in the range of 1.02 ± 0.03–1.06 ± 0.03. The StoneFil elements showed PD in the range of 1.43 ± 0.04 g.cm−3–1.46 ± 0.04 g.cm−3 and REDeff in the range of 1.31 ± 0.04–1.33 ± 0.04. The PLA phantom elements were shown to have MDA of ≤1.00 mm and DSC of ≥0.95 compared to design, and ≤0.48 mm and ≥0.91 compared like modules. The StoneFil elements displayed MDA values of ≤0.44 mm and DSC of ≥0.98 compared to design and ≤0.43 mm and ≥0.92 compared like modules. Conclusions Phantoms which were radiologically equivalent to tissue and bone were produced with a high level of similarity to design and even higher level of similarity of one another. When used in conjunction with the derived CT to PD or REDeff conversion curves they are suitable for evaluating the effects of spinal surgical implants of varying material of construction.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Physical and Radiological Densitymentioning

confidence: 99%

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Investigation of the effects of spinal surgical implants on radiotherapy dosimetry: A study of 3D printed phantoms

et al. 2021

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“…After observing that the MV CT produced dramatically different radiodensity results from the kV CT of the sample (see Section 3.1), additional radiodensity measurements were performed using a narrow (3 × 3 cm 2 ) 6 MV radiotherapy beam from a Varian Clinac 21iX (Varian Medical Systems, Palo Alto, USA), to investigate the consistency of results between using the MV CT imaging system and the MV treatment beam. A method described by Moutrie et al [6] was used to identify the "effective" relative electron density, (ρ e /ρ e,w ) eff , which is the ρ e /ρ e,w of the sample as identified using an electronic portal imaging device (EPID), for the particular therapy beam and the particular scatter conditions used to acquire the EPID image. Moutrie et al's method was also adapted as described by Dancewicz et al [7], to allow the (ρ e /ρ e,w ) eff assessment to be verified using measurements performed with a Roos ionization chamber (type 34001, PTW, Freiburg, Germany).…”

Section: Radiodensity Characterisationmentioning

confidence: 99%

“…For both the EPID measurements and the Roos chamber measurements, the water equivalent thickness of the physical sample (i.e. the thickness of water providing equivalent attenuation), t w , was measured using comparisons with Virtual Water (Standard Imaging Inc, Middleton, USA) transmission measurements, and (ρ e /ρ e,w ) eff was calculated by division of t w by the physical thickness of sample, t, as described by Moutrie et al and Dancewicz et al [6,7].…”

Section: Radiodensity Characterisationmentioning

confidence: 99%

Impact of radiopacified bone cement on radiotherapy dose calculation

Crowe

Bennett

Lathouras

et al. 2020

Physics and Imaging in Radiation Oncology

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Background and purpose: Radiopacifiers are introduced to bone cements to provide the appearance of bone in kilovoltage (kV) radiographic images. For higher energy megavoltage (MV) radiotherapy treatment beams, however, these radiopacifiers do not cause a bone-like perturbation of dose. This study therefore aimed to determine the impact of the barium-contrasted plastic-based cement materials on radiotherapy dose calculations. Materials and methods: The radiological properties of a physical sample of bone cement were characterised by computed tomography (CT) imaging and transmission measurements. Monte Carlo simulations of percentage depth-dose profiles were performed to determine the possible dose error for MV treatment beams. Dose differences were then investigated for clinical volumetric modulated radiotherapy treatment plans, with and without density overrides applied. Results: Differences of up to 7% were observed at the downstream interface of a 0.6 cm thick bone cement layer, compared to bone. Differences in planning target volume dose-volume metrics varied between −0.5% and 2.0%. Conclusion: Before planning radiotherapy treatments for patients who have undergone cranioplasty, every effort should be made to identify whether a radiopacified bone cement has been implanted. Density overrides should be applied to minimise dose calculation errors, whenever bone cement is used.

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A markerless beam's eye view motion monitoring algorithm based on structure conversion and demons registration in medical image with partial data

et al. 2023

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Purpose To propose a markerless beam's eye view (BEV) motion monitoring algorithm, which works with the inferior quality megavolt (MV) images with multi‐leaf collimator (MLC) occlusion‐compatible. Methods A thorax phantom was used to verify the accuracy of the algorithm. Lung tumor quality assurance (QA) plans were generated for the phantom, and delivered 10 times on the linear accelerator with manually treatment offsets in various directions. The algorithm was used to register 753 electronic portal imaging device (EPID) images with the appropriate digitally reconstructed radiograph (DRR), calculating a registration offset that was compared with the actual offset to determine the monitoring errors. Image similarity measure was used as an independent check. Additionally, patient data of 21 lung tumor treatment plans were gathered. A total of 533 pairs of patient images were acquired for motion monitoring study, to offer quantifiable data of the tumor position change during treatment. Results The monitoring algorithm can process various degrees (10%–80%) of image loss, and performs well when dealing with non‐rigid registration for partial data images. About 86.8% of the monitoring errors are less than 3 mm in the algorithm verification of the phantom study, and about 80% of the errors are under than 2 mm. Normalized Mutual Information (NMI) of phantom images changes from 1.182 ± 0.026 to 1.202 ± 0.027, with p < 0.005, and the Hausdorff‐Distance (HD) changes from 3.506 ± 0.417 mm to 3.466 ± 0.473 mm, with p < 0.005. Translation with a displacement range of ‐6.0 mm to 6.2 mm is the predominant change of the patient target during treatment. NMI of patient images changes from 1.216 ± 0.031 to 1.225 ± 0.031, with p < 0.005, and HD changes from 3.131 ± 0.876 mm to 3.118 ± 0.038 mm, with p < 0.005. The dice index of target before and after registration is 0.264 ± 0.336, indicating the presence of non‐negligible non‐rigid deformation. Conclusions The study provides a robust markerless motion monitoring algorithm for multi‐modal, partial data and inferior quality image processing.

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Use of a megavoltage electronic portal imaging device to identify prosthetic materials

Cited by 13 publications

References 22 publications

Investigation of the effects of spinal surgical implants on radiotherapy dosimetry: A study of 3D printed phantoms

Investigation of the effects of spinal surgical implants on radiotherapy dosimetry: A study of 3D printed phantoms

Impact of radiopacified bone cement on radiotherapy dose calculation

A markerless beam's eye view motion monitoring algorithm based on structure conversion and demons registration in medical image with partial data

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