Metal Hip Prostheses Research Articles

Stereotactic Body Radiation Therapy for Clinically Localized Prostate Cancer in Men With Hip Prostheses: A Cautionary Note.

Stereotactic body radiation therapy (SBRT) has been established as a safe and effective treatment for prostate cancer. SBRT requires high accuracy to reduce treatment margins. Metal hip prostheses create artifacts that distort pelvic imaging and potentially decrease the accuracy of target/organ at risk (OAR) identification and radiation dose calculations. Data on the safety and efficacy of SBRT after hip replacement is limited. This single-institution study sought to evaluate the safety and local control following SBRT for prostate cancer in men with hip replacements. 23 patients treated with localized prostate cancer and a history of pre-treatment hip replacement, treated with SBRT from 2007 to 2017 at MedStar Georgetown University Hospital were included in this retrospective analysis. Treatment was administered with the CyberKnife® (Accuray Incorporated, Sunnyvale, CA) at doses of 35 Gy or 36.25 Gy in 5 fractions. The targets and OARs were identified and contoured by a single experienced Radiation Oncologist (SPC).The adequacy of the CT and T2W MRI images for treatment planning was assessed with a three-point scale (good, adequate, or suboptimal).During treatment planning, care was taken to avoid treatment beams that directly traversed the hip prosthesis. Toxicities were recorded and scored using the Common Terminology Criteria for Adverse Events version 4.0 (CTCAE v.4.0). Local recurrence was confirmed by magnetic resonance imaging and/or prostate biopsy. The median follow-up was seven years. The patients were elderly (median age = 71 years) with a high rate of comorbidities (Charlson Comorbidity Index > 2 in 25%). Four patients had bilateral hip replacements. The majority of patients were low to intermediate risk per the D'Amico classification. Around 13% received upfront ADT. In total, 13 patients were treated with 35 Gy, and 10 were treated with 36.25 Gy.The rates of late > Grade 3 GU toxicity and> Grade 2 GI toxicity were 8.6% and 4.3%, respectively. There were no Grade 4 or 5 toxicities.Six patients (26%) developed a local recurrence at a median time of 7.5 years. Of these six patients, four had unilateral hip replacements and two had bilateral.Three underwent salvage cryotherapy and three received salvage ADT. In the general population, high-grade toxicities and local recurrences are uncommon following prostate SBRT.However, in this cohort of patients with prior hip replacements, prostate SBRT had higher than expected rates of late toxicity and local recurrence. In the opinion of the authors, such patients should be counseled regarding an elevated risk of late toxicity and local recurrence with prostate SBRT. With its ultrasound guidance, brachytherapy would have the advantage of circumventing the need for MRI/CT-based imaging and thus may represent a preferable radiation alternative in this patient population. If these patients are treated with SBRT, they should be monitored closely for local recurrence so early salvage can be performed. We hopethat recent advances in metal artifact reduction techniques and dose-calculation algorithms will improve future outcomes.

Investigation of Dose Calculation Accuracy of Eclipse Treatment Planning System in the Presence of Metal Hip Prosthesis with Thermoluminescence Dosimeters

Aim: This study investigated the dose calculation accuracy of different treatment planning algorithms used in radiotherapy patients with hip prostheses. Method: The current research produced a tissue-equivalent cylindrical phantom that imitates a leg using a 3D printer. Co-Cr-Mo alloy and Ti-6AI-4V alloy prostheses were placed in the centre of the phantom, respectively. Both prostheses' dose measurements were taken with thermoluminescent dosimeters (TLD) at 92 points. The dose calculation accuracy of the Analytical Anisotropic Algorithm (AAA) and Pencil Beam Convolution (PBC) algorithms, widely used in radiotherapy, were compared with the measurement results. Results: Since the Co-Cr-Mo hip prosthesis has a high density, the number of backscattered photons around it was higher than the Ti-6AI-4V hip prosthesis. The average surface dose of the Co-Cr-Mo alloy was 364.05 cGy, while the average surface dose of the Ti-6AI-4V alloy was 347.79 cGy. Conclusion: It was observed that the dose estimation abilities of the AAA and PBC algorithms decreased as the density of the hip replacement increased. In addition, the AAA algorithm predicted the surface dose in the phantom better than the PBC algorithm.

Geometric distortion caused by metallic femoral head prosthesis in prostate cancer imaging on an MR Linac: in-vivo measurements of spatial deformation.

Metallic implants cause artefacts and distortion on MRI. To ensure accurate dose delivery and plan adaptation on an MR Linac, there is a need to evaluate distortion caused. Participants were imaged on an MR Linac (Elekta Unity, Elekta AB Stockholm). Three sequences were evaluated. Two vendor supplied (T2W TSE 3D), and one T2W TSE 3D optimized to reduce metal artefact distortions. Images were rigidly registered to CT images by a single observer, using bony anatomy. Three coronal and three axial images were selected, and six paired, adjacent, bony landmarks were identified on each slice. Images bisecting treatment isocentre were included. Difference between landmark coordinates was taken to be measure of distortion. Five observers participated. Thirty six pairs of bony landmarks were identified. Median difference in position of landmarks was ≤3 mm (range 0.3-4.4 mm). One-way analysis of variance (ANOVA) between observer means showed no significant variation between sequences or patients (P = 1.26 in plane, P = 0.11 through plane). Interobserver intra class correlation (ICC) was 0.70 in-plane and 0.78 through-plane. Intra-observer ICC for three observers was 0.76, 0.81, 0.83, showing moderate to good reliability on this small cohort. This in-vivo feasibility study suggests distortion due to metallic hip prosthesis is not an obstacle for pelvic radiotherapy on an MR Linac. Research on the impact on plan quality is warranted. This work supports feasibility of treating patients with metallic hip prosthesis on an MR Linac.

Synthetic computed tomography based dose calculation in prostate cancer patients with hip prostheses for magnetic resonance imaging-only radiotherapy.

Metallic hip prostheses cause substantial artefacts in both computed tomography (CT) and magnetic resonance (MR) images used in radiotherapy treatment planning (RTP) for prostate cancer patients. The aim of this study was to evaluate the dose calculation accuracy of a synthetic CT (sCT) generation workflow and the improvement in implant visibility using metal artefact reduction sequences. The study included 23 patients with prostate cancer who had hip prostheses, of which 10 patients had bilateral hip implants. An in-house protocol was applied to create sCT images for dose calculation comparison. The study compared prostheses volumes and resulting avoidance sectors against planning target volume (PTV) dose uniformity and organs at risk (OAR) sparing. Median PTV dose difference between sCT and CT-based dose calculation among all patients was 0.1 % (-0.4 to 0.4%) (median(range)). Bladder and rectum differences (V50Gy) were 0.2 % (-0.3 to 1.1%) and 0.1 % (-0.9 to 0.5%). The median 3D local gamma pass rate for partial arc cases using a Dixon MR sequence was Γ20%2mm/2% = 99.9%. For the bilateral full arc cases, using a metal artefact reconstruction sequence, the pass rate was Γ20%2mm/2% = 99.0%. An in-house protocol for generating sCT images for dose calculation provided clinically feasible dose calculation accuracy for prostate cancer patients with hip implants. PTV median dose difference for uni- and bilateral patients with avoidance sectors remained <0.4%. The Outphase images enhanced implant visibility resulting in smaller avoidance sectors, better OAR sparing, and improved PTV uniformity.

Revealing pelvic structures in the presence of metal hip prothesis via non-circular CBCT orbits.

As the expansion of Cone Beam CT (CBCT) to new interventional procedures continues, the burdensome challenge of metal artifacts remains. Photon starvation and beam hardening from metallic implants and surgical tools in the field of view can result in the anatomy of interest being partially or fully obscured by imaging artifacts. Leveraging the flexibility of modern robotic CBCT imaging systems, implementing non-circular orbits designed for reducing metal artifacts by ensuring data-completeness during acquisition has become a reality. Here, we investigate using non-circular orbits to reduce metal artifacts arising from metallic hip prostheses when imaging pelvic anatomy. As a first proof-of-concept, we implement a sinusoidal and a double-circle-arc orbit on a CBCT test bench, imaging a physical pelvis phantom, with two metal hip prostheses, housing a 3D-printed iodine-filled radial line-pair target. A standard circular orbit implemented with the CBCT test bench acted as comparator. Imaging data collection and processing, geometric calibration and image reconstruction was completed using in-house developed software programs. Imaging with the standard circular orbit, image artifacts were observed in the pelvic bones and only 33 out of the possible 45 line-pairs of the radial line-pair target were partially resolvable in the reconstructed images. Comparatively, imaging with both the sinusoid and double-circle-arc orbits reduced artifacts in the surrounding anatomy and enabled all 45 line-pairs to be visibly resolved in the reconstructed images. These results indicate the potential of non-circular orbits to assist in revealing previously obstructed structures in the pelvic region in the presence of metal hip prosthesis.

Deep learning reconstruction with single-energy metal artifact reduction in pelvic computed tomography for patients with metal hip prostheses

PurposeThe aim of this study was to assess the impact of the deep learning reconstruction (DLR) with single-energy metal artifact reduction (SEMAR) (DLR-S) technique in pelvic helical computed tomography (CT) images for patients with metal hip prostheses and compare it with DLR and hybrid iterative reconstruction (IR) with SEMAR (IR-S).Materials and methodsThis retrospective study included 26 patients (mean age 68.6 ± 16.6 years, with 9 males and 17 females) with metal hip prostheses who underwent a CT examination including the pelvis. Axial pelvic CT images were reconstructed using DLR-S, DLR, and IR-S. In one-by-one qualitative analyses, two radiologists evaluated the degree of metal artifacts, noise, and pelvic structure depiction. In side-by-side qualitative analyses (DLR-S vs. IR-S), the two radiologists evaluated metal artifacts and overall quality. By placing regions of interest on the bladder and psoas muscle, the standard deviations of their CT attenuation were recorded, and the artifact index was calculated based on them. Results were compared between DLR-S vs. DLR and DLR vs. IR-S using the Wilcoxon signed-rank test.ResultsIn one-by-one qualitative analyses, metal artifacts and structure depiction in DLR-S were significantly better than those in DLR; however, between DLR-S and IR-S, significant differences were noted only for reader 1. Image noise in DLR-S was rated as significantly reduced compared with that in IR-S by both readers. In side-by-side analyses, both readers rated that the DLR-S images are significantly better than IR-S images regarding overall image quality and metal artifacts. The median (interquartile range) of the artifact index for DLR-S was 10.1 (4.4–16.0) and was significantly better than those for DLR (23.1, 6.5–36.1) and IR-S (11.4, 7.8–17.9).ConclusionDLR-S provided better pelvic CT images in patients with metal hip prostheses than IR-S and DLR.

Dose perturbation effects by metal hip prosthesis in gynaecological 192Ir HDR brachytherapy

The present study was conducted to elucidate the effects of hip prostheses in 192Ir HDR brachytherapy and determine dose uncertainties introduced by the treatment planning. A gynaecological phantom irradiated using Nucletron 192Ir microSelectron HDR source was modeled using MCNP5 code. Three hip materials considered in this study were water, bone, and metal prosthesis. According to the obtained results, a dose perturbation was observed within the medium with a higher atomic number, which reduced the dose to the nearby region.

The Bone Cement Hypercoagulation Syndrome: Pathophysiology, Mortality, and Prevention.

Since Charnley introduced acrylic cement to seal metallic hip prostheses in the 1950s, reports of perioperative fatal cardiorespiratory and vascular dysfunctions have been published. Studies on humans and animals have shown neurogenic stimulation and substantial local and systemic activation of coagulation are caused by surgical bone marrow damage and chemical cell destruction by toxic monomeric methyl methacrylate from the implanted cement and other tissue-released substances. Venous blood-borne cell fragments and conjugates of activated cells from the surgical site are sequestered and trapped in the pulmonary microcirculation. A substantial hypercoagulation occurs in the lung circulation. Hypercoagulable blood is passed over to the arterial side and may cause vessel obliteration and organ damage. This process may affect the brain, heart, and kidneys and, through the release of vasoactive substances, introduce hemodynamic imbalances that can lead to fatal outcomes in susceptible populations such as elderly patients with hip fractures. The main underlying pathophysiologic processes leading to these occasionally devastating outcomes are a substantial activation of coagulation and cell destruction caused by the toxic substance released by curing bone cement and several vasoactive substances.

Metal artifact reduction and iterative reconstruction algorithms in computed tomography imaging of hip prostheses

Introduction: Computed tomography (CT) of metal hip prostheses are prone to experiencing metal-related artefacts during the imaging process. The resulting low image quality can affect the surrounding tissue and the metal implant itself which can lead to the loss of relevant findings. Various techniques have been used to reduce metal artifacts, which can improve the image quality by minimising their origin.

A Effect of Radial Clearance, Corner Radius and Micro Lateralization on Contact Stress of Metallic and Ceramic Hip Prosthesis

Edge loading leads to high contact stress at the rim of the contact. This is due to less radial clearance and excessive lateral head displacement which potentially causes implant failure. The ceramic implants have a high possibility of fracture compared with metallic implants because of above-said reasons. The present study focuses on the investigation of contact stress for the combined effect of radial clearance (0.05-0.75 mm) and micro-lateralisation conditions (1-2.5 mm) for Metal-on-Metal (M-o-M) and Ceramic-on-Ceramic (C-o-C) pairs. The contact stresses are analysed for round corners of the acetabulum cup geometry for the above-said combinations with four different arc radii (1- 4mm). Finite element modeling (FEM) of femur head with half of the acetabulum cup is considered for the current study. Contact stress values obtained for 2 mm and 4 mm round corner geometry are quite low when compared with 1 and 3 mm round corners even for larger radial clearances and high lateral head displacements. The study also showed von Mises stress value obtained for M-o-M pair is quite low for 4 mm round corner for larger radial clearance and high lateral head displacements. Similarly, in C-o-C pair the compressive stress values are minimum for 4 mm round corner. Since the stress values were minimum for 4 mm round corner geometry, it clearly indicates that even edge loading occurs and the round corner geometry would be very helpful in reducing the stress for both M-o-M and C-o-C pairs.

The Effect of MAR Technique on Image Quality of the Anorectal Region in Pelvic CT in Patients with Metallic Hip Prostheses

The Effect of MAR Technique on Image Quality of the Anorectal Region in Pelvic CT in Patients with Metallic Hip Prostheses

Quantifying Distortion on MR Images of Patients with Metallic Hip Prosthesis – Will it Exclude Treatment on an MR Linac?

Purpose: The presence of metallic prosthesis will cause distortion in MR images. This may impact dose calculation and treatment delivery on a magnetic resonance linear accelerator (MR Linac). This feasibility study quantified the perceived visual distortion of MR images for patients with both prostate cancer and hip prosthesis.

A Fractal-RFID Based Sensing Tattoo for the Early Detection of Cracks in Implanted Metal Prostheses

Manufacturing faults and aging are the main causes for micro-crack generation in implanted prostheses. An early detection of surface defects by means of local sensors can prevent dangerous complications and prompt for a preventive replacement of the medical device. For this purpose, a tattoo-like sensing mechanism based on pre-fractal Space Fulling Curves is wrapped onto the medical device and coupled with a zero-power RFID transponder. The resulting smart prosthesis is capable to identify the early formation of cracks and to communicate with the exterior of the body by backscattering communication. The crack detection method exploits the anti-tamper port of common Radiofrequency Identification (RFID) ICs and a small antenna, acting as harvester, closely integrated with the metal prosthesis. Simulations and tests with a mockup of metallic hip prosthesis and a leg phantom demonstrate that the device can identify surface cracks as small as 0.6 mm and can be wireless interrogated outside the body from up to 70 cm distance. The required geometrical change to the prosthesis is modest and does not hinder its mechanical robustness. Experiments also confirmed that the health status of the prosthesis could be even monitored on-the-fly when the patient crosses a door equipped with a UHF reader. The sensorized prosthesis could hence become an enabler for the emerging Precision Medicine and for the Internet of Bodies paradigm.

Investigation of Dose Calculation Accuracy of AAA and PBC Algorithms in the Presence of Metal Hip Prosthesis

Investigation of Dose Calculation Accuracy of AAA and PBC Algorithms in the Presence of Metal Hip Prosthesis

Gel and thermoluminescence dosimetry for dose verifications of a real anatomy simulated prostate conformal radiation treatment in the presence of metallic femoral prosthesis.

This study aims to verify the dose delivery of prostate radiotherapy treatments in an adult pelvic phantom with two metallic hip and femur prosthesis using a four‐field box technique. The prostate planned target volume (PTV) tridimensional (3D) dose distribution was evaluated using gel dosimetry, and thermoluminescent dosimeters (TLD) were used for point‐dose measurements outside it. Both results were compared to the treatment planning system (TPS) dose calculation without using heterogeneity corrections to evaluate the influence of the metal in the dose distribution. MAGIC‐f gel dosimeter (Methacrylic and Ascorbic acid in Gelatin Initiated by Copper with Formaldehyde) associated with magnetic resonance imaging was used. TLD were positioned at several points at the bone metal interface and the sacrum region. The comparison of the gel measured and the TPS calculated dose distributions were done using gamma analysis (3%/3 mm), and a pass rate of 93% was achieved. The TLD dose values at the bone‐metal interface showed variations from the planned dose. However, at the sacrum region, where the beams did not intercept the prosthesis, there was a good agreement between TPS planning and TLD measurements. Our results show how the combination of 3D dosimetry and measurements at specific points in the phantom allowed a comprehensive view of the dose distribution and identified that care must also be paid to regions outside the PTV.

PO-1952 Quantification of MRI distortion in patients with metallic hip prosthesis: a feasibility study

PO-1952 Quantification of MRI distortion in patients with metallic hip prosthesis: a feasibility study

Role of hypoxia inducible factor 1α in cobalt nanoparticle induced cytotoxicity of human THP-1 macrophages.

ABSTRACTCobalt is one of the main components of metal hip prostheses and cobalt nanoparticles (CoNPs) produced from wear cause inflammation, bone lyses and cytotoxicity at high concentrations. Cobalt ions mimic hypoxia in the presence of normal oxygen levels, and activate hypoxic signalling by stabilising hypoxia inducible transcription factor 1α (HIF1α). This study aimed to assess in vitro the functional role of HIF1α in CoNP induced cellular cytotoxicity. HIF1α, lysosomal pH, tumour necrosis factor α and interleukin 1β expression were analysed in THP-1 macrophages treated with CoNP (0, 10 and 100 μg/mL). HIF1α knock out assays were performed using small interfering RNA to assess the role of HIF1α in CoNP-induced cytotoxicity. Increasing CoNP concentration increased lysosomal activity and acidity in THP-1 macrophages. Higher doses of CoNP significantly reduced cell viability, stimulated caspase 3 activity and apoptosis. Reducing HIF1αactivity increased the pro-inflammatory activity of tumour necrosis factorαand interleukin 1β,but had no significant impact on cellular cytotoxicity. This suggests that whilst CoNP promotes cytotoxicity and cellular inflammation, the apoptotic mechanism is not dependent on HIF1α.

Heating of hip joint implants in MRI: The combined effect of RF and switched-gradient fields.

PurposeTo investigate how the simultaneous exposure to gradient and RF fields affects the temperature rise in patients with a metallic hip prosthesis during an MRI session.MethodsIn silico analysis was performed with an anatomically realistic human model with CoCrMo hip implant in 12 imaging positions. The analysis was performed at 1.5 T and 3 T, considering four clinical sequences: turbo spin‐echo, EPI, gradient‐echo, and true fast imaging sequence with steady precession. The exposure to gradient and RF fields was evaluated separately and superposed, by adopting an ad hoc computational algorithm. Temperature increase within the body, rather than specific absorption rate, was used as a safety metric.ResultsWith the exception of gradient‐echo, all investigated sequences produced temperature increases higher than 1 K after 360 seconds, at least for one body position. In general, RF‐induced heating dominates the turbo spin‐echo sequence, whereas gradient‐induced heating prevails with EPI; the situation with fast imaging sequence with steady precession is more diversified. The RF effects are enhanced when the implant is within the RF coil, whereas the effects of gradient fields are maximized if the prosthesis is outside the imaging region. Cases for which temperature‐increase thresholds were exceeded were identified, together with the corresponding amount of tissue mass involved and the exposure time needed to reach these limits.ConclusionThe analysis confirms that risky situations may occur when a patient carrying a hip implant undergoes an MRI exam and that, in some cases, the gradient field heating may be significant. In general, exclusion criteria only based on whole‐body specific absorption rate may not be sufficient to ensure patients’ safety.

Using Megavoltage Computed Tomography to Estimate Radiotherapy Dose for High-Density Metallic Implants

Streak artifacts in kilovoltage computed tomography (kVCT), originated from metallic implants, are reduced by megavoltage CT (MVCT). This study aimed to establish the image value-to-density table (IVDT) of MVCT and validate dose accuracy. The IVDT of MVCT was established with different physical densities (0.290–19.427 g/cm3) and compared with kVCT for doses. The Acuros external beam (AXB) algorithm was compared with the analytical anisotropic algorithm (AAA) for heterogeneity correction in MVCT. Based on the experimental results, the IVDT of MVCT showed good linearity. Dose overestimations for the metallic hip prosthesis in a water phantom were reduced from 2.6%/2.8% in kVCT_AAA, 1.8%/−0.7% in MVCT_AAA and to −0.7%/−0.3% in MVCT_AXB with 6-MV/10-MV photons, respectively. The predictive formulas were validated and highly correlated with the measured doses ( $R^{2}= 0.9933$ /0.9862 for 6-/10-MV photons, respectively). On average, the dose differences with a metallic eye shield on the Alderson radiation therapy phantom using 6-MV photon were reduced from 3.6% in kVCT_AAA to −1% in MVCT_AAA. In patient studies, the reductions of dose overestimations were from 28.6% and 7.4% to −3.9% with dental fillings, from 13.6% and −9% to −9.1% with the unilateral hip prosthesis, and from −25.3% and −5.9% to −4.3% with bilateral hip prostheses in kVCT_AAA, MVCT_AAA, and MVCT_AXB, respectively. In conclusion, MVCT with the AXB algorithm reduces metal artifacts on kVCT and plans accurate doses.

PD-0433: Clinical workflow for treating patients with a metallic hip prosthesis on the MR-linac

PD-0433: Clinical workflow for treating patients with a metallic hip prosthesis on the MR-linac