Search

• A new analytical model for the mobilization of root reinforcement is developed. • 3-D root orientations, root slippage and non-linear root behaviour are incorporated. • The model matches the magnitude and gradual mobilization observed in experiments. • The effect of key parameters driving root reinforcement can now be quantified. Roots can stabilise slopes against shallow landslides by mobilising their mechanical strength. Existing analytical models are highly simplified and typically focus on the ultimate limit state only, thus providing little insight into the underlying mechanism of reinforcement mobilisation. A new analytical model ('DRAM') was therefore developed to predict mechanical root reinforcement as a function of direct shear displacements. This model accounts for elasto-plastic root behaviour, three-dimensional root orientations, root failure through breakage or slippage, and a dynamically changing shear zone thickness. Comparison to two independent experimental direct shear data sets showed that the model was able to accurately predict the gradual mobilisation of root strength, the magnitude of peak root reinforcement, as well as the presence of significant root reinforcement at large shear displacements, associated with a relatively large quantity of roots slipping out of the surrounding soil. Because the newly developed model more closely resembles the underlying physics of the mobilisation of root reinforcement in direct shear while still being easy to use, it will be a useful tool for the engineering industry, in terms of quantifying root reinforcement distribution for limit analyses at the ultimate limit state, as well as for directing future research into the drivers of mechanical root reinforcement. [ABSTRACT FROM AUTHOR]

We recently, developed a simple one-day one-step incubation method to obtain bone-like apatite coating on flexible and biodegradable Polyactive® 1000PEGT70PBT30. The present study reports a preliminary biological evaluation on the coated polymer after implantation in rabbit femurs. The porous cylindrical implants were produced from a block fabricated by injection molding and salt leaching. This technique provided the block necessary mechanical integrity to make small cylinders (∅3.5×5 mm2) that were suitable for implantation in rabbits. The coating continuously covered the surface of the polymer, preserving the porous architecture of outer contour of the cylinders. Two defects with a diameter of 3.5 or 4 mm were drilled in the proximal and distal part of femur diaphysis. The implants were inserted as press-fit or undersized into the cortex as well as in the marrow cavity. The polymer swelled after implantation due to hydration, leading to a tight contact with the surrounding bone in both defects. The adherence of the coating on the polymer proved to be sufficient to endure a steam sterilization process as well as the 15% swelling of the polymer in vivo. The coated Polyactive® 1000PEGT70PBT30 has a good osteoconductive property, as manifested by abundant bone growth into marrow cavity along the implant surface during 4-week implantation. A favorable bioactive effect of the coating with an intimate bone contact and extensive bone bonding with this polymer was qualitatively confirmed. Concerning the bone ingrowth into the porous implant in the defect of 4 mm diameter, only marginal bone formation was observed up to 8 weeks with a maximal penetration depth of about 1 mm. The pore interconnectivity is important not only for producing a coating inside the porous structure but also for bone ingrowth into this biodegradable material. This preliminary study provided promising evidence for a further study using a bigger animal model. [Copyright &y& Elsevier]

Of the many materials that are applied in dental implantology, most have a high Young's modulus, in the concept of osseointegration, which is generally preferred, chewing forces are therefore directly transmitted from rigid implant materials to the relatively flexible surrounding bone. Polyactive® is an elastomeric polyethylene-oxide polybutylene- terephthalate (PEO:PBT) copolymer, with a low modulus of elasticity, that exhibits bone-bonding characteristics. Previous finite-element analysis emphasized the benefit of the application of flexible implant materials. To assess the validity of this finite element model, one dense and two porous types of flexible Polyactive® permucosal dental implants and one rigid hydroxylapatite (HA) implant were clinically tested in a beagle dog study and were compared during 30 weeks of loading. In an earlier report, it was concluded that dense Polyactive® implants function clinically adequately and resemble the mobility of natural teeth, In the current study, the amount of bone contact was quantitatively assessed. Polyactive® implants showed a statistically significantly higher bone contact, as compared to the HA implants, probably due to a significant water uptake and a subsequent increase in the volume of the denser Polyactive®. Morphological analysis, based on back- scatter electron microscopy and light microscopy, revealed little remodelling activity of the bone surrounding the Polyactive® implants1 Few remodelling lacunae were seen and de novo bone formation was rarely observed. At some locations, a continuity between calcification zones with the polymer surface and the surrounding interfacial bone was observed, indicating the occurrence of bone-bonding. Also, the bone surrounding the HA implants showed little remodelling activity, although large resorption lacunae were observed, in which HA particles were present. Based on the observations of this study flexible bone bonding implants might be more capable of transferring stresses to the surrounding bone and are therefore promising alternatives to `routine' rigid implants. [ABSTRACT FROM AUTHOR]

Recently, an elastomeric polyethyleneaoxide polybutylene-terephthalate (PEO:PBT) copolymer (Polyactive®) was introduced, which exhibits bone-bonding characteristics. In contrast to ceramics, bioglass,. titanium and other metals, PEO:PBT copolymers are flexible materials that could reduce undesirable peak stresses along the neck of a permucosal implant. The application of three types of Polyactive® permucosal dental implants (one dense and two porous types) and one dense hydroxylapatite (HA) implant were clinically tested and compared during 30 weeks of loading in a dog experiment. With respect to the porous Polyadilve® implants, it was observed that the pore diameter had decreased to such an extent that optimal bone ingrowth was not achieved. Polyacflve® is known to expand due to water uptake, and, as a consequence, the sizes of the pores of the press-fit inserted implants had decreased to a large extent. This feature explained the high loss of the implants with the porous outer layer (6 out of 22). None of the dense Polyactive® implants and only one of the HA implants were lost. Statistical analysis was performed solely on the dense Polyactive® and the HA implants. At the lingual sites, plaque scores, gingiva indices, bleeding indices and corresponding pocket depths were statistically significantly lower for both implant types, when compared to the corresponding values' at the buccal, mesial and distal sites, irrespective of the observation period. Differences between the dense Polyactive® and the HA implants were not observed. A considerable difference in mobility was registered between the Polyactive® and the hydroxylapatite implants, as measured by the Periotest®, The dense Polyactive® implants functioned adequately and had mobility resembling natural teethe As such, these dense flexible materials showed a favourable clinical function and they seem promising for reducing undesired peak stresses when applied as a dental implant. [ABSTRACT FROM AUTHOR]

Abstract Magnetic resonance imaging (MRI) is often combined with computed tomography (CT) in prostate radiotherapy to optimise delineation of the target and organs-at-risk (OAR) while maintaining accurate dose calculation. Such a dual-modality workflow requires two separate imaging sessions, and it has some fundamental and logistical drawbacks. Due to the availability of new MRI hardware and software solutions, CT examinations can be omitted for prostate radiotherapy simulations. All information for treatment planning, including electron density maps and bony anatomy, can nowadays be obtained with MRI. Such an MRI-only simulation workflow reduces delineation ambiguities, eases planning logistics, and improves patient comfort; however, careful validation of the complete MRI-only workflow is warranted. The first institutes are now adopting this MRI-only workflow for prostate radiotherapy. In this article, we will review technology and workflow requirements for an MRI-only prostate simulation workflow. Highlights • MRI-only workflows are being implemented in several centres for prostate cancer; • Before the introduction of an MRI-only workflow in clinical practice, the building blocks of this workflow should be implemented and validated. • MRI-only workflows are useful both in the context of X-ray or CBCT-guided radiotherapy as well as MRI-guided radiotherapy. [ABSTRACT FROM AUTHOR]

• The smallest clinical target volume (CTV) to planned target volume (PTV) margins that yielded full dosimetric coverage for esophageal cancer radiotherapy were assessed. • Accumulated dose analysis revealed that CTV-to-PTV treatment margins of 8, 9 and 10 mm in posterior & right, anterior & cranial and left & caudal direction, respectively, are sufficient to account for interfraction tumor variations over the course of treatment when applying a daily online bone match. • Even with these rather generous margins, outlying patients still do exist who may be underdosed and need special attention. This study aimed to assess the smallest clinical target volume (CTV) to planned target volume (PTV) margins for esophageal cancer radiotherapy using daily online registration to the bony anatomy that yield full dosimetric coverage over the course of treatment. 29 esophageal cancer patients underwent six T2-weighted MRI scans at weekly intervals. An online bone-match image-guided radiotherapy treatment of five fractions was simulated for each patient. Multiple conformal treatment plans with increasing margins around the CTV were created for each patient. Then, the dose was warped to obtain an accumulated dose per simulated fraction. Full target coverage by 95% of the prescribed dose was assessed as a function of margin expansion in six directions. If target coverage in a single direction was accomplished, then the respective margin remained fixed for the subsequent dose plans. Margins in uncovered directions were increased in a new dose plan until full target coverage was achieved. The smallest set of CTV-to-PTV margins that yielded full dosimetric CTV coverage was 8 mm in posterior and right direction, 9 mm in anterior and cranial direction and 10 mm in left and caudal direction for 27 out of 29 patients. In two patients the curvature of the esophagus considerably changed between fractions, which required a 17 and 23 mm margin in right direction. Accumulated dose analysis revealed that CTV-to-PTV treatment margins of 8, 9 and 10 mm in posterior & right, anterior & cranial and left & caudal direction, respectively, are sufficient to account for interfraction tumor variations over the course of treatment when applying a daily online bone match. However, two patients with extreme esophageal interfraction motion were insufficiently covered with these margins and were identified as patients requiring replanning to achieve full target coverage. [ABSTRACT FROM AUTHOR]

• Online MR-guided soft-tissue registration protocols exhibited modest improvements of the geometric target coverage probability as compared to online CBCT-guided bone match protocols. • Therefore, highly conformal target irradiation using online MR-guidance can only be achieved by implementing on-table adaptive workflows where new treatment plans are daily generated based on the anatomy of the day. This study aimed to quantify the coverage probability for esophageal cancer radiotherapy as a function of a preset margin for online MR-guided and (CB)CT-guided radiotherapy. Thirty esophageal cancer patients underwent six T2-weighted MRI scans, 1 prior to treatment and 5 during neoadjuvant chemoradiotherapy at weekly intervals. Gross tumor volume (GTV) and clinical target volume (CTV) were delineated on each individual scan. Follow-up scans were rigidly aligned to the bony anatomy and to the clinical target volume itself, mimicking two online set-up correction strategies: a conventional CBCT-guided set-up and a MR-guided set-up, respectively. Geometric coverage probability of the propagated CTVs was assessed for both set-up strategies by expanding the reference CTV with an isotropic margin varying from 0 mm to 15 mm with an increment of 1 mm. A margin of 10 mm could resolve the interfractional changes for 118 out of the 132 (89%) analyzed fractions when applying a bone-match registration, whereas the CTV was adequately covered in 123 (93%) fractions when the registration was directly performed at the CTV itself (soft-tissue registration). Closer analyses revealed that target coverage violation predominantly occurred for distal tumors near the junction and into the cardia. Online MR-guided soft-tissue registration protocols exhibited modest improvements of the geometric target coverage probability as compared to online CBCT-guided bone match protocols. Therefore, highly conformal target irradiation using online MR-guidance can only be achieved by implementing on-table adaptive workflows where new treatment plans are daily generated based on the anatomy of the day. [ABSTRACT FROM AUTHOR]

Radiotherapy treatment of pancreatic cancer can be challenging due to close relationship between the tumor and radiosensitive intestines and poor visibility of the upper abdomen with conventional treatment methods. In recent years, with the introduction of MR-guided radiotherapy (MRgRT) it became possible to deliver ablative doses to (peri-)pancreatic tumors. In this multicenter cohort study, we report clinical outcomes from our first cohort of patients with (peri-)pancreatic tumors with MR-guided stereotactic radiotherapy on a 1.5 T MR-Linac. All patients with (peri-)pancreatic tumors treated on the 1.5 T Unity MR-Linac between April 2019 and January 2022 at two institutes. Symptoms were reported using clinician-reported outcome measurements defined by the Common Terminology Criteria for Adverse Events (CTCAE) version 5. Quality of life (QoL) was assessed with the EORTC QLQ-C30 questionnaire and evaluated with the Global Health status. Symptoms and QoL were assessed at baseline, and at three, six and twelve months after treatment. The Kaplan-Meier analysis was performed for the 6 months-, and 1-year survival. The baseline characteristics of 79 patients are summarized in Table 1. The most frequently delivered SBRT scheme was 40 Gy in 5 fractions of 8 Gy. Most frequently reported grade 3 symptoms at baseline, three months follow-up, six months, and twelve months were abdominal pain (0%, 13%, 3%, and 5%); anorexia (0%, 9%, 0%, and 0%); fatigue (0%, 5%, 6%, and 5%); nausea (0%, 5%, 0%, and 5%), and diarrhea (0%, 5%, 6%, and 5%). Other grade 3 toxicity at three months follow up occurred in 5% for malabsorption; 2% of patients for vomiting; 2% for gastroparesis; 2% for weight loss; 2% for portal hypertension and 2% for gallbladder obstruction. No treatment-related toxicities higher than grade 3 were observed in our cohort. The EORTC Global Health status was 71 at baseline (n=37), 70 after three months follow up (n=20), 65 after six months (n=12), and 67 after twelve months (n=6). From the treatment start with MRgRT, the cumulative 6 months- and 1-year survival was 88%, and 74%, respectively. In this international prospective cohort of patients with (peri-)pancreatic tumors, we observed a low incidence of major treatment-related toxicity and a stable Global Health status at three months post MRgRT on a 1.5T MR-Linac. [ABSTRACT FROM AUTHOR]

Integrated 2-[ 18 F]-fluoro-2-deoxy- d -glucose (FDG) PET/CT and magnetic resonance imaging (MRI) with functional features of diffusion-weighted imaging (DWI) are advancing imaging technologies that have current and future potential to overcome important limitations of conventional staging methods in the management of patients with oesophageal cancer. PET/CT has emerged as an important part of the standard work-up of patients with oesophageal cancer. Besides its important ability to detect unsuspected metastatic disease, PET/CT may be useful in the assessment of treatment response, radiation treatment planning, and detection of recurrent disease. In addition, high-resolution T2-weighted MRI and DWI have potential complementary roles. Recent improvements in MRI protocols and techniques have resulted in better imaging quality with the potential to bring improvement in staging, radiation treatment planning, and the assessment of treatment response. Optimal use and understanding of PET/CT and MRI in oesophageal cancer will contribute to the impact of these advancing technologies in tailoring treatment to the individual patient and achieving best possible outcomes. In this article, we graphically outline the current and potential future roles of PET/CT and MRI in the multidisciplinary management of oesophageal cancer. [ABSTRACT FROM AUTHOR]

Summary: Although the benefit of extra-oral implants in the reconstruction of maxillofacial oncological defects is undisputable, some relevant issues need to be clarified. The purpose of this retrospective study was to evaluate the relationship between implants placed during ablation (DA-implants) and after ablation (AA-implants) of the tumor with respect to implant survival. In total, 103 implants were assessed: 44 nasal implants (17 patients) and 59 orbital implants (18 patients). All patients received their implant-retained maxillofacial epithesis between 1997 and 2010, with a mean follow-up of 35months (range 8–156months). The survival rate of DA-implants was 90.0% for the orbital region and 93.5% for the nasal region. The survival rate of the AA-implants for the orbital and the nasal region was 82.8% and 61.5%, respectively. This study shows a significant higher survival rate of extra-oral implants placed during ablative surgery compared to implants in a later stage (p =0.044), thereby stressing the importance of installing extra-oral implants during the ablative surgical session. [Copyright &y& Elsevier]

In this paper a new model for the hydro-mechanical behaviour of rooted soils is developed. It is a physically-based model that couples finite strain soil deformation with unsaturated water and air flow, while improving on existing cohesion-based approaches to mechanical root reinforcement and empirical soil water-uptake approaches typically used to deal with rooted slopes. The model is used to show that the dynamics of soil-water pressure and soil deformation depend strongly on the physics of the root-water uptake and the elasto-plastic soil mechanics. Root water uptake can cause suctions and corresponding soil shrinkage sufficiently large to necessitate a finite-strain approach. Although this deformation can change the intrinsic permeability, hydraulic conductivity remains dominated by the water content. The model incorporates simultaneous air-flow, but this is shown to be unimportant for soil-water dynamics under the conditions assumed in example simulations. The mechanical action of roots is incorporated via a root stress tensor and a simulation is used to show how root tension is mobilised within a swelling soil. The developed model may be used to simulate both laboratory experiments and full-scale vegetated slopes. [ABSTRACT FROM AUTHOR]