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Results for “Polymethyl Methacrylate”

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At least 307 records · Page 17Linked to original sources

PubMed2005

In vivo study of liposomes as drug carriers to oral mucosa using EPR oximetry.

The purpose of this study was to select the best types of liposomes for use as drug carriers for topical treatment of oral mucosal lesions. Electron paramagnetic resonance (EPR) oximetry, using the paramagnetic probe lithium phthalocyanine, was used in vivo to measure the effects of a hyperemic drug, benzyl nicotinate (BN) which was incorporated into liposomes of varying size and composition. The liposomes were made from either hydrogenated or non-hydrogenated soy lecithin and mixed with polymethyl methacrylate ointment for application. EPR oximetry was used to measure the partial pressure of oxygen (pO2) in the oral mucosa before and after application of liposomes. It was found that the most pronounced changes of pO2 in oral mucosa and also the longest action of the drug occurred after the topical application of BN in multi-lamellar liposomes made from hydrogenated soy lecithin (p<0.0001). When these liposomes were applied to oral mucosa over 3 successive days it was found that pO2 increased the most on the first day, the effect gradually decreased following application on the second and third days. The duration of the resulting hyperemia was the longest on the second day (p<0.01). Among the examined carriers, multi-lamellar liposomes made from hydrogenated soy lecithin appear to be the most appropriate for local drug delivery to oral mucosa.

Animals↗

PubMed2003

In vitro calcium phosphate growth over surface modified PMMA film.

In vitro nucleation of calcium phosphate phase was studied over functionalized polymethyl methacrylate (PMMA) films using Fourier transform infrared spectroscopy, electron spectroscopy, scanning electron microscopy and energy dispersive X-ray analysis. PMMA films were prepared by dissolving commercial grade pellets in chloroform and cast into thin sheets. The films were immersed in a methanol solution of sodium hydroxide before treating with 1.5% solution of adenosine triphosphate (ATP) at a pH of 5.2 for 24 h. ATP treated films were then soaked in saturated lime solution for 4 days to initiate formation of calcium phosphate precursor phase over their surface. The above films immersed in simulated body fluid solution (1.5 x SBF) for more than 5 days led to the nucleation of apatitic calcium phosphate phase all over the film surface. The ATP coupled film not subjected to lime treatment did not show calcium phosphate nucleation behaviour upon immersion in SBF solution. The Ca/P ratio of the calcium phosphate phase increase with increase in soaking time in SBF solution.

Calcium Phosphates↗

PubMed2005

Some factors governing the efficacy of positional pseudoaccommodative intraocular lenses.

PURPOSE: To examine the effects of ametropia (spherocylindrical), corneal curvature, target anterior chamber depth (ACD), misplacement, and some design features on the performance of positional pseudoaccommodative intraocular lenses (PPAIOLs). DESIGN: Theoretical investigation based on computer models to determine the practical limitations of PPAIOLs. METHODS: Using a suitable model eye featuring gradient index optics within the cornea, the PPAIOL curvatures were calculated for axial ametropia ranging from -10 diopters (D) to +10 D, where the IOL was located at an ACD of 4.05 mm. The change in refraction (y) of the hypothetical pseudophakic eye was calculated for each millimeter of forward movement (x) of the PPAIOL up to 1 mm from the pole of the corneal back surface. The computations were repeated for a range of hypothetical PPAIOL refractive indices (1.49-1.70), ACDs, equiconvex and meniscus (back surface radius, -10 mm and -25 mm), corneal astigmatism (-1 D to -5 D), and radii (after corneal refractive surgery). MAIN OUTCOME MEASURES: Diopter/millimeter values represent the gradient of the relationship between x and y. Mathematical models describe the association between the diopter/millimeter gradient and key clinical dependent variables. RESULTS: (1) For a polymethyl methacrylate (refractive index, 1.49) PPAIOL of equiconvex design and 4.05-mm ACD, the predicted diopter/millimeter value is a function of ametropia (a), where diopter/millimeter = 1.666+0.136a+0.0018a2. (2) For 6-mm ACD and a refractive index of 1.7, diopter/millimeter = 1.836+0.159a+0.0027a2. (3) The equiconvex design benefits hyperopic but not myopic eyes. (4) For PPAIOLs correcting >4 D of astigmatism, more than 0.5 D of residual astigmatism is present at near after 1 mm of IOL displacement. (5) In emmetropic cases, the predicted diopter/millimeter value is a function of the corneal radius (r) where diopter/millimeter = 7.376-1.162r+0.0545r2. (6) Positional pseudoaccommodative IOL misplacement does not significantly affect the accommodative ability. CONCLUSIONS: (1) Hyperopic eyes with relatively steep corneas should benefit more from the PPAIOL than myopic eyes with relatively flat corneas. (2) A full, binocular, near refraction should be performed to correct any residual spheroastigmatism in anisometropia and cases in which the PPAIOL is toric.

Accommodation, Ocular↗

PubMed2003

Design of a new water-soluble pressure-sensitive adhesive for patch preparation.

This work was intended to improve the adhesion properties of an available medical water-soluble pressure-sensitive adhesive (PSA) through the addition of cellulose ethers or polyvinylpyrrolidone (PVP). The adhesion properties were evaluated by means of peel adhesion test and creep resistance test. Possible interactions between the polymethyl methacrylate (PMMA) and hydrocolloid were investigated by Fourier-transformed infrared spectroscopy. Moreover, a central composite design was used to estimate the effects of hydrocolloids and plasticizers and their interactions on the PSA performance. The addition of PVP made it possible to obtain a patch with a 40-fold improved creep compliance and a reduced peel adhesion. The significant increase of the matrix cohesion was due to attractive interactions between the amide group of PVP and the carboxylic acid group of PMMA. The water vapor permeability of the prepared systems was very high. Furthermore, no primary skin irritation was observed. The presence of plasticizers at high level increased both the peel values and creep compliance, showing an opposite behavior with respect to PVP. The new PSA system can be easily removed from the skin, is suitable for repeated applications on the same site, and has adhesive properties that can be modified by changing the component ratios.

Adhesives↗

PubMed2000

Influence of intraocular lens material and design on postoperative intracapsular cellular reactivity.

PURPOSE: To evaluate the influence of intraocular lens (IOL) material and design on the outcome of postoperative lens epithelial cell proliferation within the capsular bag after cataract surgery. METHODS: A total of 5,079 human globes containing rigid and foldable posterior chamber IOL styles commonly implanted in the United States (n = 8) were analyzed in this study. Each globe, fixated in 10% formalin, was sectioned at the equator and analyzed using the Miyake-Apple posterior technique. The study consisted of 3 parts: First, to evaluate posterior capsule opacification (PCO); the Nd:YAG laser posterior capsulotomy rate (%) was documented and plotted on a monthly basis, creating a computerized trend line for each IOL style. Second, to evaluate anterior capsule opacification (ACO); 460 globes were processed for histologic examination. Anterior capsule fibrosis was scored from 0 to III, according to the thickness of proliferative tissue/cells on the inner surface of the anterior capsule at the capsulorhexis margin. Third, interlenticular opacification (ILO) was studied by analysis of 3 pairs of acrylic piggyback lenses that had been explanted because of opacification between their optics. Each IOL pair was processed for histologic examination, and scanning electron microscopy was performed on 1 of the lenses. RESULTS: In the first study, relatively higher Nd:YAG laser posterior capsulotomy rates (19.1% to 32.8%) were noted with the 4 oldest IOL designs in this study (2 foldable lenses, 1 3-piece polymethyl methacrylate [PMMA] design, and 1 single-piece all-PMMA design). Four modern lenses, 1 acrylic lens, and 3 silicone foldable IOL designs had Nd:YAG rates ranging from 1.3% to 14.6% (P < .0001). In the second study, mean ACO scores were highest with silicone-plate lenses (1.77 +/- 0.86 and 1.28 +/- 0.77). The lowest mean score was observed with the acrylic lens (0.51 +/- 0.52; P < .0001). In study 3, the analyses of the 3 pairs of explanted acrylic piggyback lenses showed that the opacification between them (ILO) may have different forms. CONCLUSIONS: Control of postoperative intracapsular cellular proliferation is important in avoiding 3 significant clinical complications. Postoperative lens epithelial cell proliferation is involved in the pathogenesis of PCO, ACO, and ILO, the latter being a newly described form of opacification within the capsular bag related to piggyback IOL implantation. IOL material and design are important factors influencing the outcome of these complications.

Acrylates↗

PubMed2005

Adhesion of echinoderm tube feet to rough surfaces.

Echinoderms attach strongly and temporarily to the substratum by means of specialized organs, the podia or tube feet. The latter consist of a basal extensible cylinder, the stem, which bears an apical flattened disc. The disc repeatedly attaches to and detaches from the substratum through adhesive and de-adhesive secretions. In their activities, echinoderms have to cope with substrata of varying degrees of roughness as well as with changing hydrodynamic conditions, and therefore their tube feet must adapt their attachment strength to these environmental constraints. This study is the first attempt to evaluate the influence of substratum roughness on the temporary adhesion of echinoderm tube feet and to investigate the material properties of their contact surface. It was demonstrated that tube foot discs are very soft (E-modulus of 6.0 and 8.1 kPa for sea stars and sea urchins, respectively), have viscoelastic properties and adapt their surface to the substratum profile. They also show increased adhesion on a rough substratum in comparison to its smooth counterpart, which is due mostly to an increase in the geometrical area of contact between the disc and the surface. Tenacity (force per unit area) increases with roughness [e.g. 0.18 and 0.34 MPa on smooth polymethyl-methacrylate (PMMA), 0.21 and 0.47 MPa on rough PMMA for sea stars and sea urchins, respectively] if only the projected surface area of the adhesive footprint is considered. However, if this tenacity is corrected to take into account the actual substratum 3-D profile, surface roughness no longer influences significantly the corrected adhesion strength (e.g. 0.18 and 0.34 MPa on smooth PMMA, 0.19 and 0.42 MPa on rough PMMA for sea stars and sea urchins, respectively). It can be hypothesized that, under slow self-imposed forces, disc material behaves viscously to adapt to substratum roughness while the adhesive fills out only very small surface irregularities (in the nanometer range). It is deposited as a thin film ideal for generation of strong adhesion. Under short pulses of wave-generated forces, attached discs probably behave elastically, distributing the stress along the entire contact area, in order to avoid crack generation and thus precluding disc peeling and tube foot detachment.

Adhesiveness↗

PubMed2004

Evaluation of mechanical and thermal properties of commonly used denture base resins.

PURPOSE: The purpose of this investigation was to evaluate and compare the mechanical and thermal properties of 6 commonly used polymethyl methacrylate denture base resins. MATERIALS AND METHODS: Sorption, solubility, color stability, adaptation, flexural stiffness, and hardness were assessed to determine compliance with ADA Specification No. 12. Thermal assessments were performed using differential scanning calorimetry and dynamic mechanical analysis. Results were assessed using statistical and observational analyses. RESULTS: All materials satisfied ADA requirements for sorption, solubility, and color stability. Adaptation testing indicated that microwave-activated systems provided better adaptation to associated casts than conventional heat-activated resins. According to flexural testing results, microwaveable resins were relatively stiff, while rubber-modified resins were more flexible. Differential scanning calorimetry indicated that microwave-activated systems were more completely polymerized than conventional heat-activated materials. CONCLUSION: The microwaveable resins displayed better adaptation, greater stiffness, and greater surface hardness than other denture base resins included in this investigation. Elastomeric toughening agents yielded decreased stiffness, decreased surface hardness, and decreased glass transition temperatures.

Adsorption↗

PubMed2001

Effect of chromatic aberration on contrast sensitivity in pseudophakic eyes.

OBJECTIVE: To evaluate the effect of chromatic aberrations in pseudophakic eyes with various types of intraocular lenses (IOLs). PATIENTS AND METHODS: The study included 51 eyes of 33 patients who underwent cataract surgery. The eyes were divided into 3 groups according to the material from which their IOL was made: group 1, polymethyl methacrylate; group 2, silicone; and group 3, an acrylate/methacrylate copolymer. Ten normal phakic control eyes (group 4) underwent the same examination. Best-corrected distance visual acuity and contrast sensitivity were measured under white light and monochromatic light with wavelengths of 470 nm, 549 nm, and 630 nm, with the best correction under white light. RESULTS: There were no significant differences in best-corrected visual acuity and contrast sensitivity under the 549-nm monochromatic light in any group. However, under both white multichromatic light and 470- and 630-nm monochromatic light, the mean contrast sensitivity in group 3 tended to be lower, sometimes significantly, than in the other IOL groups. CONCLUSIONS: Our results showed that longitudinal chromatic aberrations of some IOLs may degrade the quality of the retinal image. Attention must be paid to the detailed optical performance of IOL materials to achieve good visual function.

Acrylates↗

PubMed2002

Characterization of new acrylic bone cements prepared with oleic acid derivatives.

Acrylic bone-cement formulations were prepared with the use of a new tertiary aromatic amine derived from oleic acid, and also by incorporating an acrylic monomer derived from the same acid with the aim of reducing the leaching of toxic residuals and improving mechanical properties. 4-N,N dimethylaminobenzyl oleate (DMAO) was used as an activator in the benzoyl-peroxide radical cold curing of polymethyl methacrylate. Cements that contained DMAO exhibited much lower polymerization exotherm values, ranging between 55 and 62 C, with a setting time around 16--17 min, depending on the amine/BPO molar ratio of the formulation. On curing a commercial bone cement, Palacosreg R with DMAO, a decrease of 20 C in peak temperature and an increase in setting time of 7 min were obtained, the curing parameters remaining well within limits permitted by the standards. In a second stage, partial substitution of MMA by oleyloxyethyl methacrylate (OMA) in the acrylic formulations was performed, the polymerization being initiated with the DMAO/BPO redox system. These formulations exhibited longer setting times and lower peak temperatures with respect to those based on PMMA. The glass transition temperature of the experimental cements were lower than that of PMMA cement because of the presence of long aliphatic chains of both activator and monomer in the cement matrix. Number average molecular weights of the cured cements were in the range of 1.2x10(5). PMMA cements cured with DMAO/BPO revealed a significant (p<0.001) increase in the strain to failure and a significant (p<0.001) decrease in Young's modulus in comparison to Palacosreg R, whereas ultimate tensile strength remained unchanged. When the monomer OMA was incorporated, low concentrations of OMA provided a significant increase in tensile strength and elastic modulus without impairing the strain to failure. The results demonstrate that the experimental cements based on DMAO and OMA have excellent promise for use as orthopaedic and/or dental grouting materials.

Acrylates↗

PubMed2006

Map kinase c-JUN N-terminal kinase mediates PMMA induction of osteoclasts.

Erosive osteolysis induced by implant-derived wear debris is mediated by recruitment and activation of osteoclasts in a pro-inflammatory microenvironment that is enriched with osteoclastogenic and pro-inflammatory cytokines such as RANKL and tumor necrosis factor alpha (TNF-alpha). These cytokines activate the transcription factor NF-kappaB and MAP kinases, including c-Jun, Erks, and p38, all known to be essential for the development of osteoclasts. We have recently documented that TNF and RANKL play a pivotal role in the development of inflammatory osteolysis. We have also found that polymethyl methacrylate (PMMA) particles stimulate osteoclastogenesis, at least in part, by induction of RANKL, TNF, and by activation of NF-kappaB and MAP kinases. More importantly, our data indicate that inhibitors of NF-kappaB and the MAP kinases p38 and ERK abrogate particle-induced osteoclastogenesis. In the current study, we investigated if inhibition of c-Jun N-Terminal kinase (JNK) pathway alters PMMA-induced osteoclastogenesis. Our findings point out that PMMA particles activate the JNK pathway in wild-type and TLR4-null (endotoxin-resistant) osteoclast precursors. This activation was selectively blocked in a dose-dependent fashion by the JNK inhibitor SP600125. Most importantly, we provide evidence that SP600125 inhibits osteoclast formation in a reversible manner. Collectively, our findings demonstrate that activation of the JNK pathway is essential for basal and PMMA-stimulated osteoclastogenesis, and buttress the potential significance of targeting the JNK pathway to inhibit osteolysis.

Animals↗

PubMed2005

Dynamic flat panel detector versus image intensifier in cardiac imaging: dose and image quality.

The practical aspects of the dosimetric and imaging performance of a digital x-ray system for cardiology procedures were evaluated. The system was configured with an image intensifier (II) and later upgraded to a dynamic flat panel detector (FD). Entrance surface air kerma (ESAK) to phantoms of 16, 20, 24 and 28 cm of polymethyl methacrylate (PMMA) and the image quality of a test object were measured. Images were evaluated directly on the monitor and with numerical methods (noise and signal-to-noise ratio). Information contained in the DICOM header for dosimetry audit purposes was also tested. ESAK values per frame (or kerma rate) for the most commonly used cine and fluoroscopy modes for different PMMA thicknesses and for field sizes of 17 and 23 cm for II, and 20 and 25 cm for FD, produced similar results in the evaluated system with both technologies, ranging between 19 and 589 microGy/frame (cine) and 5 and 95 mGy min(-1) (fluoroscopy). Image quality for these dose settings was better for the FD version. The 'study dosimetric report' is comprehensive, and its numerical content is sufficiently accurate. There is potential in the future to set those systems with dynamic FD to lower doses than are possible in the current II versions, especially for digital cine runs, or to benefit from improved image quality.

Air↗

PubMed1999

Interfacial strength between molded UHMWPE and PMMA-MMA monomer treated UHMWPE.

To solve aseptic loosening of cemented acetabular cup and tibial plateaus of hips and knee joint prostheses in total joint replacement, adhesion between the polymeric prostheses made of ultra-high molecular weight polyethylene (UHMWPE) and bone cement made of polymethyl-methacrylate (PMMA) has been investigated. Previous studies using xylene, PMMA, and MMA monomer solution to treat bulk surfaces of UHMWPE resulted in 11.5 +/- 0.65 MPa as the maximum interfacial strength between the treated UHMWPE and bone cement. The present study eliminates the use of xylene; instead, UHMWPE powders were treated with MMA monomer and PMMA-MMA solution, dried, and then compression-molded with untreated UHMWPE powders. The interfacial tensile strengths were measured and the best molding conditions investigated by varying temperature, pressure, and time. Temperature was the predominant factor when compared to that of pressure or time. The maximum interfacial strength between the treated UHMWPE and untreated UHMWPE was 16.3 +/- 0.94 MPa with the molding conditions of 166.5 degrees C, 38.7 MPa, and 1 h. Scanning electron microscopic (SEM) pictures show the coating of the nodules and fibrils of UHMWPE powder with PMMA. Pulled out aggregated nodular space and coated PMMA after fracture could be seen easily from PMMA-MMA treated UHMWPE powder.

Acetabulum↗

PubMedDate not supplied

Comparative assessment of three in vitro exposure methods for combustion toxicity.

A comparative assessment of three approaches for the use of human cells in vitro to investigate combustion toxicity was conducted. These included one indirect and two direct (passive and dynamic) exposure methods. The indirect method used an impinger system in which culture medium was used to trap the toxicants, whilst the direct exposure involved the use of a Horizontal Harvard Navicyte Chamber at the air/liquid interface. The cytotoxic effects of thermal decomposition products were assessed using the MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) assay (Promega) on a selection of human cells including: HepG2, A549 and skin fibroblasts. A small scale laboratory fire test using a vertical tube furnace was designed for the generation of combustion products. Polymethyl methacrylate (PMMA) was selected as a model polymer to study the cytotoxic effects of combustion products. NOAEC (no observable adverse effect concentration), IC10 (10% inhibitory concentration), IC50 (50% inhibitory concentration) and TLC (total lethal concentration) values were determined from dose response curves. Assessment using the NRU (neutral red uptake) and ATP (adenosine triphosphate) assays on human lung derived cells (A549) was also undertaken. Comparison between in vitro cytotoxicity results against published toxicity data for PMMA combustion and predicted LC50 (50% lethal concentration) values calculated from identified compounds using GCMS (gas chromatography mass spectrometry) was determined. The results suggested that the indirect exposure method did not appear to simulate closely exposure via inhalation, whilst exposure at the air/liquid interface by using the dynamic method proved to be a more representative method of human inhalation. This exposure method may be a potential system for in vitro cytotoxicity testing in combustion toxicity.

Adenosine Triphosphate↗

PubMed2001

Influence of various hemodialysis membranes on the plasma (1-->3)-beta-D-glucan level.

BACKGROUND: Recently, invasive fungal infections have increased significantly because of the growing number of immunocompromised hosts. The measurement of plasma (1-->3)-beta-D-glucan has been proposed as a useful diagnostic tool for deep mycosis. In this study, we analyzed the alteration of the plasma (1-->3)-beta-D-glucan concentration by using different kinds of hemodialysis (HD) membranes in end-stage renal disease (ESRD) patients and estimated its half-life. METHODS: Twenty-seven patients with ESRD without known fungal infections (with a median age of 66 years old) were enrolled in this study. Cellulose triacetate (CTA) membrane, cellulose (Cu) membrane, and polymethyl methacrylate (PMMA) membrane were used in three consecutive initiations of HD and plasma (1-->3)-beta-D-glucan concentration was measured before and after each HD session. RESULTS: The level did not change between before and after HD when CTA and PMMA membranes were used. In contrast, the plasma (1-->3)-beta-D-glucan level increased greatly after HD using the Cu membrane (from 9.4 to 332 pg/mL in median). Hypothesizing that the plasma (1-->3)-beta-D-glucan level declines exponentially, its median half-life is estimated at 20 hours, which is not affected by hepatic or renal function. CONCLUSIONS: Because the plasma (1-->3)-beta-D-glucan level increases dramatically after HD using the Cu membrane, dialyzers with Cu membrane should be avoided for HD in patients with suspected deep mycosis. The measurement of plasma (1-->3)-beta-D-glucan is also useful for the patients with hepatic or renal failure.

Adult↗

PubMedDate not supplied

Multiple unit gastroretentive drug delivery systems: a new preparation method for low density microparticles.

The aim of this study was to develop a new preparation method for low density foam-based, floating microparticles and to demonstrate the systems' performance in vitro. Major advantages of the novel preparation technique include: (i) short processing times, (ii) no exposure of the ingredients to high temperatures, (iii) the possibility to avoid toxic organic solvents, and (iv) high encapsulation efficiencies close to 100%. Floating microparticles consisting of polypropylene foam powder, model drug [chlorpheniramine maleate (CPM), diltiazem HCl, theophylline or verapamil HCl] and polymer [Eudragit RS or polymethyl methacrylate (PMMA)] were prepared by soaking the microporous foam carrier with an organic solution of drug and polymer and subsequent drying. The effects of various formulation and processing parameters on the resulting in vitro floating behaviour, internal and external particle morphology, drug loading, in vitro drug release and physical state of the incorporated drug were studied. Good in vitro floating behaviour was observed in most cases and a broad variety of drug release patterns could be achieved by varying the drug loading and type of polymer. Interestingly, PMMA-based microparticles showed incomplete drug release with verapamil HCl. This restriction could be overcome by forming the free base of the drug prior to microparticle preparation. In contrast to the salt, the free base acted as a plasticizer for PMMA, resulting in sufficiently high diffusion coefficients and, consequently, complete drug release. The low density microparticles were compressed into rapidly disintegrating tablets in order to provide an administrable oral dosage form.

Administration, Oral↗

PubMed2003

The use of bone cement induces an increase in serum astroglial S-100B protein in patients undergoing total knee arthroplasty.

UNLABELLED: Cerebral microemboli can occur during arthroplasty with the use of bone cement. Astroglial S-100B protein is a sensitive marker of cerebral damage. Therefore, we designed this study to determine the effect of bone cement on the brain by investigating serum levels of S-100B protein in patients undergoing bone surgery with or without bone cement. Fourteen patients undergoing knee arthroplasty (n = 7) or reamed intramedullary nailing for tibial fracture (n = 7) requiring a pneumatic tourniquet were enrolled in this study. Bone cement containing polymethyl methacrylate and methyl methacrylate was used for every patient undergoing knee arthroplasty. Serum samples were obtained from venous blood before the induction of general anesthesia, 15 min after deflation of a pneumatic tourniquet, and 3 days after the operation. The serum level of S-100B protein was significantly increased 15 min after a pneumatic tourniquet deflation in the knee arthroplasty group compared with the tibial fracture group (0.41 and 0.08 ng/mL, respectively; P < 0.05). In all patients studied, no neurological abnormalities were noted in the postoperative period. These results suggest that, in patients undergoing knee arthroplasty, bone cement may transiently induce astroglial injury, although it does not alter neurological outcome. IMPLICATIONS: Serum S-100B protein was significantly increased 15 min after a pneumatic tourniquet deflation in patients undergoing knee arthroplasty with bone cement, but not in those undergoing reamed intramedullary nailing for tibial fracture without bone cement. These results suggest that bone cement may transiently induce astroglial injury.

Aged↗

PubMed2001

Application of the new MultiTrans SP3 radiation transport code in BNCT dose planning.

Dose planning in boron neutron capture therapy (BNCT) is a complex problem and requires sophisticated numerical methods. In the framework of the Finnish BNCT project, new deterministic three-dimensional radiation transport code MultiTrans SP3 has been developed at VTT Chemical Technology, based on a novel application of the tree multigrid technique. To test the applicability of this new code in a realistic BNCT dose planning problem, cylindrical PMMA (polymethyl-methacrylate) phantom was chosen as a benchmark case. It is a convenient benchmark, as it has been modeled by several different codes, including well-known DORT and MCNP. Extensive measured data also exist. In this paper, a comparison of the new MultiTrans SP3 code with other methods is presented for the PMMA phantom case. Results show that the total neutron dose rate to ICRU adult brain calculated by the MultiTrans SP3 code differs less than 4% in 2 cm depth in phantom (in thermal maximum) from the DORT calculation. Results also show that the calculated 197Au(n,gamma) and 55Mn(n,gamma) reaction rates in 2 cm depth in phantom differ less than 4% and 1% from the measured values, respectively. However, the photon dose calculated by the MultiTrans SP3 code seems to be incorrect in this PMMA phantom case, which requires further studying. As expected, the deterministic MultiTrans SP3 code is over an order of magnitude faster than stochastic Monte Carlo codes (with similar resolution), thus providing a very efficient tool for BNCT dose planning.

Adult↗

PubMed2001

A computational study into the use of polyacrylamide gel and A-150 plastic as brain tissue substitutes for boron neutron capture therapy.

A precise evaluation of the dosimetric performance of epithermal neutron beams designed for boron neutron capture theory of brain tumours requires the use of a phantom material that closely matches brain tissue. The aim of this study was to investigate how well polyacrylamide gel (or PAG) and A- 150 plastic performed as substitutes for brain tissue compared with standard phantom materials such as water and polymethyl-methacrylate (or PMMA). Thermal neutron fluence, photon dose and epithermal neutron dose distributions were calculated for the epithermal neutron beam available at the University of Birmingham. The results presented in this paper show that the PAG provides a good simulation of radiation transport in the brain with differences from the real brain of +9.4%, - 10.8% and +5.1% at a depth of 50 mm for thermal neutron fluence, gamma dose and epithermal neutron dose distributions respectively. The polyacrylamide gel presented is therefore a promising substitute for brain tissue that can, as a dosimeter, provide a three-dimensional map of the absorbed dose delivered by the epithermal neutron beam. However, this study does not investigate the agreement between doses derived from magnetic resonance and physical doses for such gels. A- 150 plastic was shown to be a better substitute for brain tissue than PMMA, with differences from brain of -1.9%, -12.4% and - 13.2% at a depth of 50 mm for thermal neutron fluence, gamma dose and epithermal neutron dose distributions respectively, against +21.1%, -16.2% and +19.2% for PMMA. A-150 plastic should therefore be the material of choice for solid phantoms.

Acrylic Resins↗