Titanium Inserts Research Articles

Load to failure of different zirconia implant abutments with titanium components

Statement of problemAbutments with a zirconia superstructure and a titanium insert have recently become popular. Although they have been tested under static load, their performance under simulated mastication is not well known. PurposeThe purpose of this in vitro study was to compare the cyclic load to failure of 3 types of zirconia abutments with different mechanisms of retention of the zirconia to the titanium interface. Material and methodsFifteen implants (n=5 per system) and abutments (3 groups: 5 friction fit [Frft]; 5 bonded; and 5 titanium ring friction fit [Ringfrft]) were used. Abutments were thermocycled in water between 5°C and 55°C for 15000 cycles and then cyclically loaded for 20000 cycles or until failure at a frequency of 2 Hz by using a sequentially increased loading protocol up to a maximum of 720 N. The load to failure for each group was recorded, and 1-way analysis of variance was performed. ResultsThe mean load-to-failure values for the Frft group was 526 N, for the Bond group 605 N, and for the Ringfrft group 288 N. A statistically significant difference was found among all abutments tested (P<.05). ConclusionsAbutments with the bonded connection showed the highest load-to-failure value, and the abutment with the titanium ring friction fit connection showed the lowest load-to-failure value.

Custom CAD-CAM healing abutment and impression coping milled from a poly(methyl methacrylate) block and bonded to a titanium insert

This article describes a technique in which a custom-made computer-aided design and computer-aided manufacturing (CAD-CAM) healing abutment milled from a poly(methyl methacrylate) (PMMA) block is fabricated and bonded to a titanium metal insert. An impression is made during dental implant surgery, and the CAD-CAM custom-made healing abutment is fabricated before second-stage surgery while appropriate healing time is allowed for the dental implant to osseointegrate. The contours of the healing abutment are based on the contours of a tentatively designed definitive prosthesis. The healing tissue obtains contours that will be compatible with the contours of the definitive prosthesis. After the milling process is complete, a titanium metal insert is bonded to the healing abutment. Placement of the custom-made CAD-CAM healing abutment at second-stage surgery allows the tissue to obtain contours similar to those of the definitive prosthesis. A custom-made CAD-CAM impression coping milled from a PMMA block and with a titanium insert is used for the definitive impression after the soft tissue has healed. This technique allows guided soft tissue healing by using a custom-made CAD-CAM healing abutment and impression coping.

Effect of surface treatments on titanium alloy bonding to lithium disilicate glass-ceramics

Statement of problemThe esthetic challenges of using all-titanium alloy abutments have led to the increasing use of prefabricated titanium inserts bonded to tooth-colored abutments and fixed dental prostheses. Optimal bonding protocols related to the titanium alloy treatment have not been established. PurposeThe purpose of this in vitro study was to evaluate the effects of different surface treatments and cementation procedure combinations of titanium-6aluminum-4vanadium alloy (Ti6Al4V) disks on the bond strength of lithium disilicate glass-ceramics. Material and methodsA total of 100 computer-aided designed and computer-aided manufacturing (CAD-CAM) Ti6Al4V disks (4×6.6 mm) were used. As-milled specimens, without surface treatment, were used as controls. Surface treatment variables including alumina airborne-particle abrasion (50 μm, 0.4 MPa, 10 seconds, at 20-mm distance), ceramic etchant gels (5% and 9.5%), and buffered hydrofluoric (HF) acid etching, and etching times (30 and 90 seconds) were assessed. Heat-pressed lithium disilicate disks were fabricated and bonded with resin cements onto the treated surfaces (10 groups; n=10/group) according to the manufacturers' instructions. After 5000 cycles of thermal cycling, a shear bond strength test was conducted using a universal testing machine and a customized fixture with crosshead speed of 5 mm/min. ANOVA and Tukey honest significant differences tests were used for statistical analysis (α=.05). Representative specimens were observed using stereomicroscopy and scanning electron microscopy to determine the surface patterns after different treatments. ResultsThe mean ±SD bond strength values ranged from 13.1 ±6.9 MPa to 53.0 ±9.7 MPa. Statistically significant higher shear bond strength values were obtained using airborne-particle abrasion alone or etching with 9.5% HF for 30 seconds without airborne-particle abrasion (P<.05). Resin cements tested in this study had a similar effect on the bonding strength values (P>.05). ConclusionsIndividual treatments with alumina airborne-particle abrasion alone or etching with 95% HF for 30 seconds improved shear bond strength. However, combining alumina airborne-particle abrasion with different HF etching procedures did not.

Assessment of reliability of CAD-CAM tooth-colored implant custom abutments

Statement of problemInformation is lacking about the fatigue resistance of computer-aided design and computer-aided manufacturing (CAD-CAM) tooth-colored implant custom abutment materials. PurposeThe purpose of this in vitro study was to investigate the reliability of different types of CAD-CAM tooth-colored implant custom abutments. Material and methodsZirconia (Lava Plus), lithium disilicate (IPS e.max CAD), and resin-based composite (Lava Ultimate) abutments were fabricated using CAD-CAM technology and bonded to machined titanium-6 aluminum-4 vanadium (Ti-6Al-4V) alloy inserts for conical connection implants (NobelReplace Conical Connection RP 4.3×10 mm; Nobel Biocare). Three groups (n=19) were assessed: group ZR, CAD-CAM zirconia/Ti-6Al-4V bonded abutments; group RC, CAD-CAM resin-based composite/Ti-6Al-4V bonded abutments; and group LD, CAD-CAM lithium disilicate/Ti-6Al-4V bonded abutments. Fifty-seven implant abutments were secured to implants and embedded in autopolymerizing acrylic resin according to ISO standard 14801. Static failure load (n=5) and fatigue failure load (n=14) were tested. Weibull cumulative damage analysis was used to calculate step-stress reliability at 150-N and 200-N loads with 2-sided 90% confidence limits. Representative fractured specimens were examined using stereomicroscopy and scanning electron microscopy to observe fracture patterns. ResultsWeibull plots revealed β values of 2.59 for group ZR, 0.30 for group RC, and 0.58 for group LD, indicating a wear-out or cumulative fatigue pattern for group ZR and load as the failure accelerating factor for groups RC and LD. Fractographic observation disclosed that failures initiated in the interproximal area where the lingual tensile stresses meet the compressive facial stresses for the early failure specimens. Plastic deformation of titanium inserts with fracture was observed for zirconia abutments in fatigue resistance testing. ConclusionsSignificantly higher reliability was found in group ZR, and no significant differences in reliability were determined between groups RC and LD. Differences were found in the failure characteristics of group ZR between static and fatigue loading.

Formation of active sites in titanium-containing zeolites with MFI structure in propylene epoxidation with hydrogen peroxide

Propylene epoxidation with hydrogen peroxide on titanosilicates with different Si/Ti ratios and various states of titanium in the catalysts, prepared by hydrothermal crystallization according to two different procedures, has been investigated. It has been demonstrated that a change in the pH of the crystallizing gel leads to a change in the sequence of titanium insertion in the zeolite structure at a hydrothermal synthesis temperature of 170°C. It was shown that titanium incorporated in the zeolite framework in the tetrahedral positions is an active site in the epoxidation reaction, whereas titanium in the form of titanium dioxide leads to unproductive degradation of hydrogen peroxide.

Single-energy intensity modulated proton therapy

In this note, an intensity modulated proton therapy (IMPT) technique, based on the use of high single-energy (SE-IMPT) pencil beams, is described.The method uses only the highest system energy (226 MeV) and only lateral penumbra to produce dose gradient, as in photon therapy. In the study, after a preliminary analysis of the width of proton pencil beam penumbras at different depths, SE-IMPT was compared with conventional IMPT in a phantom containing titanium inserts and in a patient, affected by a spinal chordoma with fixation rods.It was shown that SE-IMPT has the potential to produce a sharp dose gradient and that it is not affected by the uncertainties produced by metal implants crossed by the proton beams. Moreover, in the chordoma patient, target coverage and organ at risk sparing of the SE-IMPT plan resulted comparable to that of the less reliable conventional IMPT technique. Robustness analysis confirmed that SE-IMPT was not affected by range errors, which can drastically affect the IMPT plan.When accepting a low-dose spread as in modern photon techniques, SE-IMPT could be an option for the treatment of lesions (e.g. cervical bone tumours) where steep dose gradient could improve curability, and where range uncertainty, due for example to the presence of metal implants, hampers conventional IMPT.

Acoustic-emission testing of multiple-pass welding defects of large-size constructions

Four passes were performed in the welding process of a 700-mm diameter pipe and 1800 × 1800-mm size steel sheet with a hole for the pipe. Welding defects were simulated by embedding artificial defects at the root of the welded seam (pores, cracks, slag, faulty fusions, and titanium inserts) and violating the welding procedure. The quality of the welded connection during the welding process was evaluated by the acoustic-emission method. After the completion of the welding the specimen underwent ultrasonic and radiographic inspection.

Dosimetric impact of orthopedic metal artifact reduction (O-MAR) on Spine SBRT patients.

The dosimetric impact of orthopedic metal artifact reduction (O‐MAR) on spine SBRT patients has not been comprehensively studied, particularly with spinal prostheses in high‐dose gradient regions. Using both phantom and patient datasets, we investigated dosimetric effects of O‐MAR in combination of various metal locations and dose calculation algorithms. A physical phantom, with and without a titanium insert, was scanned. A clinical patient plan was applied to the artifact‐free reference, non‐O‐MAR, and O‐MAR phantom images with the titanium located either inside or outside of the tumor. Subsequently, five clinical patient plans were calculated with pencil beam and Monte Carlo (iPlan) on non‐O‐MAR and O‐MAR patient images using an extended CT‐density table. The dose differences for phantom plans and patient plans were analyzed using dose distributions, dose‐volume histograms (DVHs), gamma index, and selected dosimetric endpoints. From both phantom plans and patient plans, O‐MAR did not affect dose distributions and DVHs while minimizing metal artifacts. Among patient plans, we found that, when the same dose calculation method was used, the difference in the dosimetric endpoints between non‐O‐MAR and O‐MAR datasets were small. In conclusion, for spine SBRT patients with spinal prostheses, O‐MAR image reconstruction does not affect dose calculation accuracy while minimizing metal artifacts. Therefore, O‐MAR images can be safely used for clinical spine SBRT treatment planning.PACS numbers: 87.53.Bn, 87.55.K‐, 87.57.Q‐, 87.57.cp

The effect of titanium insert repairs on the static strength of CFRP coupons and joints

In engineering industry, the panels manufacturing implicates the risk of having defects or damages due to deviations in the assembly and machining processes. A hole’s repair solution adopts the installation of titanium insert(s), avoiding the use of bigger fasteners. The fundamental requirement is to continue to guarantee high performances and efficiency of the jointed panels of the aircraft. Although this technique is diffused in metallic structures, its use is far from being completely understood in the case of composites (CFRP). In addition, differently from metals, the failure mechanisms of a composite joint are more complicated, since they vary with material properties, geometrical parameters and stress concentrations.For the above reasons, static tests are performed on different types of coupons and joints, manufactured from a carbon fiber/epoxy material and joined by countersunk fasteners. Coupons with nominal fasteners are taken as reference, while, in the remaining samples, selected holes are repaired using different inserting principles.All the tests are carried out until the final failure, in order to obtain results of the ultimate strength, especially related to the influence on the occurred failure mode(s). It is also highlighted that the assessment of the load transfer between the joint parts, and the stress distribution depend on the chosen inserting principle (countersunk/cylindrical and symmetrical/asymmetrical), on the size and on the location of repair inserts. Extensometers are used to measure relative displacements between the composite plates. Strain gauge measurements are performed on one family of coupons, in order to analyze the strain distribution in the area nearest to the hole in case of insert installed.

EVALUATION OF THE EFFECT OF CHOLECALCIFEROL ON TITANIUM IMPLANT OSSEOINTEGRATION (AN EXPERIMENTAL STUDY)

Introduction: Cholecalciferol (Vitamin D3) is essential for bone mineralization and for the subsequent maintenance of bone quality. Supplementation with Cholecalciferol (vitamin D3) is reported to show positive effects on bone mineral density Objectives: Evaluation of the effect of Cholecalciferol on dental implant osseointegration. Materials and Methods: The study was conducted on fourteen adult male mongrel dogs.Dogs were divided equally into two groups, control group and study group, seven dogs in each group. Extraction of mandibular right premolar and insertion of immediate titanium implant had been done for all dogs in both groups, and then only the dogs of the study group received Cholecalciferol for four weeks. Histological and radiographical evaluations were carried out after twelve weeks postoperatively for both groups. Results: Histological results revealed improved bone healing in the study group, as shown by marked osteoblastic activity and accelerated woven bone formation, and absence of chronic inflammatory cells. The highest rate of bone ingrowth occurred in the study group. Radiograghical evaluation revealed that the peri-implant bone density had increased significantly in the study group. Conclusion: These results indicated that Cholecalciferol vitamin D3 has systemic effects on accelerating bone formation around titanium implant

Forge Welding of Magnesium Alloy to Aluminum Alloy Using a Cu, Ni, or Ti Interlayer

The forge-welding process was examined to develop a high-strength bonding application of magnesium (Mg) alloy to aluminum (Al) alloy under high-productivity conditions. The effect of the insert material on the tensile strength of the joints, under various preheat temperatures and pressures, was investigated by analyzing the reaction layers of the bonded interface. The tensile strengths resulting from direct bonding, using pure copper (Cu), pure nickel (Ni), and pure titanium (Ti) inserts were 56, 100, 119, and 151 MPa, respectively. The maximum joint strength reached 93 pct with respect to the Mg cast billet. During high-pressure bonding, a microscopic plastic flow occurred that contributed to an anchor effect and the generation of a newly formed surface at the interface, particularly prominent with the Ti insert in the form of an oxide layer. The bonded interfaces of the maximum-strength inserts were investigated using scanning electron microscopy–energy-dispersive spectroscopy and electron probe microanalysis. The diffusion reaction layer at the bonded interface consisted of brittle Al-Mg intermetallics having a thickness of approximately 30 μm. In contrast, for the three inserts, the thicknesses of the diffusion reaction layer were infinitely thin. For the pure Ti insert, exhibiting the maximum tensile strength value among the inserts tested, focused ion beam–transmission electron microscopy–EDS analysis revealed a 60-nm-thick Al-Ti reaction layer, which had formed at the bonded interface on the Mg alloy side. Thus, a high-strength Al-Mg bonding method in air was demonstrated, suitable for mass production.

Modeling the reactive sputter deposition of Ti-doped VOx thin films**Project partially supported by the National Natural Science Foundation of China (Grant Nos. 61405027, 61421002, and 61235006) and the Postdoctoral Science Foundation of China (Grant No. 2014M562296).

In this paper an original numerical model, based on the standard Berg model, is used to simulate the growth mechanism of Ti-doped VOx deposited with changing oxygen flow during reactive sputtering deposition. Ti-doped VOx thin films are deposited using a V target with Ti inserts. The effects of titanium inserts on the discharge voltage, deposition rate, and the ratio of V/Ti are investigated. By doping titanium in the vanadium target, the average sputtering yield decreases. In this case, the sputter erosion reduces, which is accompanied by a reduction in the deposition rate. The ratio between V content and Ti content in the film is measured using energy-dispersive x-ray spectroscopy (EDX). A decrease in the vanadium concentration with the increasing of the oxygen flow rate is detected using EDX. Results show a reasonable agreement between numerical and experimental data.

Fracture strength study of internally connected zirconia abutments reinforced with titanium inserts.

The implant-abutment connection area is known to be the weakest part of an internal-connection zirconia abutment and therefore the most likely to fracture. The aim of this study was to evaluate the complementary effect of a titanium insert on the fracture strength of a zirconia abutment. Three types of abutments with internal connection structures were selected and assembled: titanium abutment-titanium abutment screw (Ti-Ti), zirconia abutment-titanium abutment screw (Zr-Ti), and zirconia abutment-titanium insert-titanium abutment screw (Zr+Ti-Ti). Fifteen abutments and 15 implants were used and divided into three groups of five specimens each. Compressive loading was applied to the specimens at 30 degrees off-axis with dislocation speed of 1 mm/min and was increased until deformation occurred. The Ti-Ti specimens showed the highest maximum fracture load, followed by the Zr+Ti-Ti specimens; the Zr-Ti assemblies were the weakest. Significant differences in fracture strength were found between the groups. All of the investigated Zr abutments fractured. However, in the Zr+Ti-Ti specimens, 60% of the Ti abutment screws fractured and 40% bent, whereas all of the abutment screws in the Zr-Ti group were only bent. The Ti insert, as a substitute for the weakest part of a Zr abutment in an implant with an internal friction connection, can reinforce the fracture strength of a Zr abutment.

Influence of preparation depths on the fracture load of customized zirconia abutments with titanium insert.

PURPOSEThis study evaluated the fracture load of customized zirconia abutments with titanium insert according to preparation depths, with or without 5-year artificial aging.MATERIALS AND METHODSThirty-six identical lithium disilicate crowns (IPS e.max press) were fabricated to replace a maxillary right central incisor and cemented to the customized zirconia abutment with titanium insert on a 4.5×10 mm titanium fixture. Abutments were fabricated with 3 preparation depths (0.5 mm, 0.7 mm, and 0.9 mm). Half of the samples were then processed using thermocycling (temperature: 5-55℃, dwelling time: 120s) and chewing simulation (1,200,000 cycles, 49 N load). All specimens were classified into 6 groups depending on the preparation depth and artificial aging (non-artificial aging groups: N5, N7, N9; artificial aging groups: A5, A7, A9). Static load was applied at 135 degrees to the implant axis in a universal testing machine. Statistical analyses of the results were performed using 1-way ANOVA, 2-way ANOVA, independent t-test and multiple linear regression.RESULTSThe fracture loads were 539.28 ± 63.11 N (N5), 406.56 ± 28.94 N (N7), 366.66 ± 30.19 N (N9), 392.61 ± 50.57 N (A5), 317.94 ± 30.05 N (A7), and 292.74 ± 37.15 N (A9). The fracture load of group N5 was significantly higher than those of group N7 and N9 (P<.017). Consequently, the fracture load of group A5 was also significantly higher than those of group A7 and A9 (P<.05). After artificial aging, the fracture load was significantly decreased in all groups with various preparation depths (P<.05).CONCLUSIONThe fracture load of a single anterior implant restored with lithium disilicate crown on zirconia abutment with titanium insert differed depending on the preparation depths. After 5-year artificial aging, the fracture loads of all preparation groups decreased significantly.

TS-1 coated microreactor for selective oxidations

A TS-1 catalyst layer has been coated inside a capillary microreactor by the transformation of a porous silica precoating using an in-situ hydrothermal synthesis method. The use of the silica precoating to favour TS-1 nucleation and growth on the microchannel surface has shown to provide a final TS-1 coating of high surface area and titanium loading with good stability. The ability to transform the silica precoating to a TS-1 coating was achieved by correctly balancing the silica precoating dissolution, zeolite nucleation and growth rates, and insertion of titanium into the zeolite framework. The 4μm TS-1 coating, consisting of TS-1 crystals of approximately 800nm in size, was applied in the epoxidation of propene as a model reaction to demonstrate its catalytic activity. The TS-1 microreactor obtained a propylene oxide productivity of 2gPO/gcath with a propylene oxide selectivity above 90%. Long-term stability tests of the TS-1 microreactor showed that the TS-1 coating is very stable with only a small deactivation noted over a 500h time-on-stream period.

The development of a defect-rejection procedure for multiple-pass welding by the distribution of the principal parameters of acoustic-emission signals

During quality control of welding, rejection levels were determined using the comparison of the distribution of the parameters of acoustic-emission (AE) signals with introduced defects represented by titanium and tungsten inserts. The MARSE energy parameter, the mean number of oscillation along the leading edge of an AE signal, and the two-interval coefficient were used as the principal informative parameters that are most sensitive to welding defects. The Student-t and Kolmogorov-Smirnov criteria with the calculation of rejection levels and their localization allow the location of defects in the course of multiple-pass welding.

SU-E-T-396: Dosimetric Accuracy of Proton Therapy for Patients with Metal Implants in CT Scans Using Metal Deletion Technique (MDT) Artifacts Reduction

Purpose: To evaluate the dosimetric accuracy for proton therapy patients with metal implants in CT using metal deletion technique (MDT) artifacts reduction. Methods: Proton dose accuracies under CT metal artifacts were first evaluated using a water phantom with cylindrical inserts of different materials (titanium and steel). Ranges and dose profiles along different beam angles were calculated using treatment planning system (Eclipse version 8.9) on uncorrected CT, MDT CT, and manually-corrected CT, where true Hounsfield units (water) were assigned to the streak artifacts. In patient studies, the treatment plans were developed on manually-corrected CTs, then recalculated on MDT and uncorrected CTs. DVH indices were compared between the dose distributions on all the CTs. Results: For water phantom study with 1/2 inch titanium insert, the proton range differences estimated by MDT CT were with 1% for all beam angles, while the range error can be up to 2.6% for uncorrected CT. For the study with 1 inch stainless steel insert, the maximum range error calculated by MDT CT was 1.09% among all the beam angles compared with maximum range error with 4.7% for uncorrected CT. The dose profiles calculated on MDT CTs for both titanium and steel inserts showed very good agreements with the ones calculated on manually-corrected CTs, while large dose discrepancies calculated using uncorrected CTs were observed in the distal end region of the proton beam. The patient study showed similar dose distribution and DVHs for organs near the metal artifacts recalculated on MDT CT compared with the ones calculated on manually-corrected CT, while the differences between uncorrected and corrected CTs were much pronounced. Conclusion: In proton therapy, large dose error could occur due to metal artifact. The MDT CT can be used for proton dose calculation to achieve similar dose accuracy as the current clinical practice using manual correction.

SU‐E‐I‐75: Evaluation of An Orthopedic Metal Artifact Reduction (O‐MAR) Algorithm On Patients with Spinal Prostheses Near Spinal Tumors

Purpose:To evaluate the impact of a commercial orthopedic metal artifact reduction (O‐MAR) algorithm on CT image quality and dose calculation for patients with spinal prostheses near spinal tumors.Methods:A CT electron density phantom was scanned twice: with tissue‐simulating inserts only, and with a titanium insert replacing solid water. A patient plan was mapped to the phantom images in two ways: with the titanium inside or outside of the spinal tumor. Pinnacle and Eclipse were used to evaluate the dosimetric effects of O‐MAR on 12‐bit and 16‐bit CT data, respectively. CT images from five patients with spinal prostheses were reconstructed with and without O‐MAR. Two observers assessed the image quality improvement from O‐MAR. Both pencil beam and Monte Carlo dose calculation in iPlan were used for the patient study. The percentage differences between non‐OMAR and O‐MAR datasets were calculated for PTV_min, PTV_max, PTV_mean, PTV_V100, PTV_D90, OAR_V10Gy, OAR_max, and OAR_D0.1cc.Results:O‐MAR improved image quality but did not significantly affect the dose distributions and DVHs for both 12‐bit and 16‐ bit CT phantom data. All five patient cases demonstrated some degree of image quality improvement from O‐MAR, ranging from small to large metal artifact reduction. For pencil beam, the largest discrepancy was observed for OARV_10Gy at 5.4%, while the other seven parameters were ≤0.6%. For Monte Carlo, the differences between non‐O‐MAR and O‐MAR datasets were ≤3.0%.Conclusion:Both phantom and patient studies indicated that O‐MAR can substantially reduce metal artifacts on CT images, allowing better visualization of the anatomical structures and metal objects. The dosimetric impact of O‐MAR was insignificant regardless of the metal location, image bit‐depth, and dose calculation algorithm. O‐MAR corrected images are recommended for radiation treatment planning on patients with spinal prostheses because of the improved image quality and no need to modify current dose constraints.This work was supported by a research grant from Philips Healthcare. Paul Klahr is an employee of Philips Healthcare.

Post-processing sets of tilted CT volumes as a method for metal artifact reduction.

BackgroundMetal implants, surgical clips and other foreign bodies may cause ‘streaking’ or ‘star’ artifacts in computed tomography (CT) reconstructions, for example in the vicinity of dental restorations or hip implants. The deteriorated image quality complicates contouring and has an adverse effect on quantitative planning in external beam therapy.MethodsThe potential to reduce artifacts by acquisition of tilted CT reconstructions from different angles of the same object was investigated. While each of those reconstructions still contained artifacts, they were not necessarily in the same place in each CT. By combining such CTs with complementary information, a reconstructed volume with less or even without artifacts was obtained. The most straightforward way to combine the co-registered volumes was to calculate the mean or median per voxel. The method was tested with a calibration phantom featuring a titanium insert, and with a human skull featuring multiple dental restorations made from gold and steel. The performance of the method was compared to established metal artifact reduction (MAR) algorithms. Dose reduction was tested.ResultsIn a visual comparison, streaking artifacts were strongly reduced and details in the vicinity of metal foreign bodies became much more visible. In case of the calibration phantom, average bias in Hounsfield units was reduced by 94% and per-voxel-errors and noise were reduced by 83%. In case of the human skull, bias was reduced by 95% and noise was reduced by 94%. The performance of the method was visually superior and quantitatively compareable to established MAR algorithms. Dose reduction was viable.ConclusionsA simple post-processing method for MAR was described which required one or more complementary scans but did not rely on any a priori information. The method was computationally inexpensive. Performance of the method was quantitatively comparable to established algorithms and visually superior in a direct comparison. Dose reduction was demonstrated, artifacts could be reduced without compromising total dose to the patient.

The impact of low-Z and high-Z metal implants in IMRT: A Monte Carlo study of dose inaccuracies in commercial dose algorithms

The aim of the study was to evaluate the dosimetric impact of low-Z and high-Z metallic implants on IMRT plans. Computed tomography (CT) scans of three patients were analyzed to study effects due to the presence of Titanium (low-Z), Platinum and Gold (high-Z) inserts. To eliminate artifacts in CT images, a sinogram-based metal artifact reduction algorithm was applied. IMRT dose calculations were performed on both the uncorrected and corrected images using a commercial planning system (convolution/superposition algorithm) and an in-house Monte Carlo platform. Dose differences between uncorrected and corrected datasets were computed and analyzed using gamma index (Pγ<1) and setting 2 mm and 2% as distance to agreement and dose difference criteria, respectively. Beam specific depth dose profiles across the metal were also examined. Dose discrepancies between corrected and uncorrected datasets were not significant for low-Z material. High-Z materials caused under-dosage of 20%-25% in the region surrounding the metal and over dosage of 10%-15% downstream of the hardware. Gamma index test yielded Pγ<1>99% for all low-Z cases; while for high-Z cases it returned 91% < Pγ<1< 99%. Analysis of the depth dose curve of a single beam for low-Z cases revealed that, although the dose attenuation is altered inside the metal, it does not differ downstream of the insert. However, for high-Z metal implants the dose is increased up to 10%-12% around the insert. In addition, Monte Carlo method was more sensitive to the presence of metal inserts than superposition/convolution algorithm. The reduction in terms of dose of metal artifacts in CT images is relevant for high-Z implants. In this case, dose distribution should be calculated using Monte Carlo algorithms, given their superior accuracy in dose modeling in and around the metal. In addition, the knowledge of the composition of metal inserts improves the accuracy of the Monte Carlo dose calculation significantly.