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At least 1,225 records · Page 68Linked to original sources
PubMed1980

Electron microscopic observations of concentric lamellar bodies within mesenchymal cells of anagen hair dermal papilla.

The presence of 2 forms of the concentric lamellar bodies was observed in the mesenchymal cells within dermal papilla of normal scalp anagen hairs. They are those composed of agranular membrane arrays in association with beta-glycogen particles (glycogen bodies) and those of smooth-surfaced endoplasmic reticulum (smooth-surfaced lamellar bodies). On rare occasions these 2 forms of the concentric lamellar bodies were simultaneously present within the same cells. Transitional forms between the smooth-surfaced lamellar bodies and phagosegresomal granules were also encountered.

Adolescent↗
PubMed1992

Clonal origin of skin and bone tumors produced by repeated beta-irradiation in mosaic cell mice.

Clonal origin of skin and bone tumors produced by repeated beta-irradiation was determined by using mice with cellular mosaicism created by random X-chromosome inactivation, on the basis of phosphoglycerate kinase-1 (PGK). The backs of female C3H/He (Pgk-1a/Pgk-1b) mice were exposed to beta rays from 90Sr-90Y at a dose of 3 Gy per exposure 3 times weekly until tumors appeared. The cumulative tumor incidence reached 100% 500 days after the beginning of irradiation, as determined by the Kaplan-Meier method. All 8 tumors examined were of a single PGK phenotype: 5 squamous cell carcinomas and 2 osteosarcomas of A-type, and 1 squamous cell carcinoma of B-type. The absence of double PGK phenotype (AB-type) tumors indicated the monoclonal origin of the tumors produced by repeated irradiation.

Animals↗
PubMed1993

Effect of an inhibitor of tumor promotion, alpha-Difluoromethylornithine, on tumor induction by repeated beta irradiation in mice.

alpha-Difluoromethylornithine (DFMO) is an inhibitor of putrescine biosynthesis and of tumor promotion. Studies were made of its effect on induction of skin and bone tumors by repeated beta irradiation of the back of female ICR mice 3 times weekly at a dose of 3 Gy per exposure. When given at a concentration of 10 mg/ml in the drinking water, DFMO significantly delayed the time of tumor emergence and decreased the yield of skin tumors, although the cumulative tumor incidence computed by the Kaplan-Meier method finally reached 100%. These results indicate that tumor-promoting activity is involved in repeated beta irradiation, besides its tumor-initiating activity.

Animals↗
PubMed2005

Quantification of dose perturbation by plaque in vascular brachytherapy.

BACKGROUND: Dose prescription and reporting in vascular brachytherapy (VBT) is based on the assumption that the vessel wall is water equivalent, which does not consider a possible dose perturbation by plaque. As the extent of this perturbation is unknown, we aimed to quantify dose attenuation by atherosclerotic plaque for beta- and gamma-radiation. MATERIAL AND METHODS: The dose delivered from Strontium-90/Yttrium-90 ((90)Sr/Y) and Iridium-192 ((192)Ir) sources with and without human peripheral arteries ((90)Sr/Y: n = 38, (192)Ir: n = 7) surrounding the respective delivery catheter was determined with radiochromic films. Plaque and vessel wall thickness were measured using light microscopy. From the ratio-attenuated doseunattenuated dose (dose perturbation factor: DPF) we determined averaged attenuation coefficients for atherosclerotic plaque (micro(P)) and the residual part of the vessel wall (micro(W)) by regression analysis based on the function DPF = exp(-micro(P) * plaque thickness -micro(W) * residual wall thickness). RESULTS: Attenuation in case of (192)Ir was less than the measurement uncertainties. For beta-radiation correlation was found by discrimination between calcified and noncalcified plaque. Classifying noncalcified plaque as normal arterial tissue, the regression coefficient was r = 0.845 at micro(P)= 0.5356 mm(-1) and micro(W) = 0.0663 mm(-1). CONCLUSIONS: Vascular brachytherapy with beta radiation in calcified arteries results in significant dose attenuation within the vessel wall, which can be calculated on knowing the vascular morphometry. Thus, plaque thickness should be taken into account in treatment planning and retrospective analyses.

Arteriosclerosis↗
PubMed1975

Cathodoluminescence of biological molecules, macromolecules and cells.

Cathodoluminescence observations on biological compounds are compared with previously established data from ultra violet and visible light excitation studies. The comparison demonstrates that the same molecules are responsible for the luminescence properties of macromolecules independent of the type of exciting radiation. Natural cathodoluminescence was also observed from cells. Moreover, advantages gained by the absorption of strongly cathodoluminiscent dyes into cells are demonstrated.

Adenine↗
PubMed1991

Treatment of pterygia in Queensland.

All practising ophthalmologists in Queensland completed a written survey on their current methods of treatment of pterygia. The indications for surgical removal, in decreasing order of importance, were mainly size, symptomatic complaints, cosmetic appearance and activity. Most surgeons graded pterygia into a variety of classifications. The most common form of treatment for primary pterygia was simple excision plus mobilisation of conjunctiva and suturing conjunctival free edges together followed by bare sclera technique, and simple excision plus thiotepa drops. For recurrent pterygia simple excision plus beta-irradiation was the most common form of treatment, followed by simple excision plus thiotepa drops and simple excision plus mobilisation of conjunctiva and suturing conjunctival free edges together. A third of the ophthalmologists electively avoid cautery use during pterygium surgery, while almost a quarter of the ophthalmologists attempt to polish the corneal and limbal region. When beta-radiation or Thiotepa is used there is a general consensus on the dosage for each of these. Seventeen per cent of ophthalmologists said they had not encountered any complications after pterygium surgery with the remainder quoting corneoscleral necrosis from beta-radiation and Tenon's granuloma as the most common complications. It would appear that there is no consensus on the best way to treat pterygia in Queensland, which probably reflects the lack of scientific proof for one method being superior to another.

Australia↗
PubMedDate not supplied

Treatment of advanced squamous cell carcinomas involving the equine cornea.

Corneal squamous cell carcinomas with surface areas of more than 2.0 cm were diagnosed in 26 eyes of 25 horses. The depth of the lesion into the corneal stroma and involvement of the ocular adnexa were important determinants for surgical treatment. Corneal tumors that extended into adjacent palpebral conjunctiva, eyelid, or orbit were not amenable to complete excision, while those that involved only cornea and bulbar conjunctiva were treated surgically by keratectomy and beta radiation. Initial treatment was keratectomy followed by beta radiation on 24 eyes and enucleation of two eyes. Twenty keratectomy patients remained tumor free after long-term follow-up. One was lost to follow-up and three recurred. The recurrences were retreated with subsequent cure (one horse), enucleation (one horse), or euthanasia (one horse).

Animals↗
PubMed2006

Pathological effects of pulmonary vein beta-radiation in a swine model.

INTRODUCTION: Atrial fibrillation (AF) may be triggered by ectopic beats originating in sleeves of atrial myocardium entering the pulmonary veins (PVs). PV isolation by means of circumferential ostial or atrial radiofrequency ablation is an effective but also a difficult and long procedure, requiring extensive applications that can have serious potential complications. Our objective was to examine pathological effects of PV beta-radiation, particularly the ability to destroy PV myocardial sleeves without inducing PV stenosis and other unwanted effects, in order to establish its potential feasibility for the treatment of AF. METHODS AND RESULTS: Ten minipigs were studied. A phosphorus-32 source wire centered within a 2.5-mm diameter balloon catheter (Galileo III Intravascular Radiotherapy System, Guidant, Santa Clara, CA, USA) was used to deliver beta-radiation to the superior wall of the right PV trunk. Pathological analysis was performed either immediately after ablation (2 pigs) or 81 +/- 27 days later (8 pigs). Acute effects of PV beta-radiation consisted of endothelial denudation covered by white thrombus, elastic lamina disruption, and PV sleeve necrosis. Late effects consisted of mild focal neointimal hyperplasia that reduced the PV luminal area by only 1.3 +/- 1.8%, elastic lamina thickening, and PV sleeve fibrosis. Four of these 8 PVs were completely re-endothelized. Lesions were transmural in 6 of 10 radiated PVs and segmental, involving 28 +/- 7% of the right PV perimeter. CONCLUSION: Intravascular beta-radiation can induce transmural necrosis and fibrosis of PV myocardial sleeves without PV stenosis and other unwanted effects, which supports a potential usefulness of this energy source in the treatment of AF.

Animals↗
PubMed2001

Intracoronary beta radiation: state of the art.

This state-of-the-art review is intended to explore the development of beta radiation including catheter delivered and permanent implants from its inception to current practice. Specific focus will be given to the isotopes currently available, radiation physics of beta emitters, preclinical studies, clinical trials, beta radiation delivery systems, and implications for future practice. The encouraging results from the clinical trials have established vascular brachytherapy as a standard of care for patients with in-stent restenosis. Vascular brachytherapy requires additional "fine-tuning" to achieve full optimization.

Beta Particles↗
PubMed2006

Predictors of recurrent in-stent restenosis after beta-radiation: An analysis from the START 40/20 trial.

OBJECTIVE: The purpose of this study was to identify potential predictors, including clinical, procedural, angiographic, and intravascular ultrasound (IVUS) parameters, for recurrent in-stent restenosis (ISR) following beta-radiation 90Strontium/Yttrium (90Sr/Y) in a large multicenter trial. BACKGROUND: Although adjunct brachytherapy reduces recurrent ISR after primary catheter-based intervention, recurrence of stenosis after brachytherapy still occurs. METHODS: We analyzed 185 IVUS cohort patients in the STent And Restenosis Therapy (START) 40/20 trial where a 40-mm, 90Sr/Y, radioactive source train was exclusively used for treatment of ISR to be treatable with a 20-mm balloon. RESULTS: Thirty-nine patients underwent target lesion revascularization. Preliminary univariate analysis showed that age, smoking, balloon/artery ratio, geographic miss, minimum lumen diameter, and diameter stenosis at baseline were associated with target lesion revascularization, while none of IVUS variables were (minimum lumen area, minimum stent area, or residual plaque burden). The multivariate logistic regression analysis showed that younger age, lower balloon/artery ratio, and presence of geographic miss were independent predictors of target lesion revascularization. CONCLUSIONS: Even with adjunct beta-radiation therapy, initial mechanical optimization, such as appropriate balloon sizing and positioning, may be critical for the prevention of recurrent ISR.

Adult↗
PubMed1978

Ultrastructural and cytochemical observations on sporogenesis of Myxobolus sp. (Myxosporida: Myxobolidae) from the common shiner Notropis cornutus.

The structure and cytochemistry of spores of Myxobolus sp. from plasmodia which occur in the gill filaments of the common shiner Notropis cornutus were studied by light microscopy and by scanning and transmission electron microscopy. The thin-walled valves of the pyriform spores are thickened in the lateral sutural and apical regions. Mucous material is associated predominantly with the posterior end of many spores. The plasmodium is surrounded by a syncytial wall bounded by 2 membranes. Pinocytotic channels are formed by the inner membrane and numerous dense vesicles are pinched off at the distal ends of the channels. Sporogenesis is initiated by the envelopment of one vegetative cell by another. The larger, enveloped cell divides to form a disporous pansporoblast, which contains 2 pairs of capsulogenic and valvogenic cells and 2 binucleate sporoplasm cells. Each capsular primordium and connecting external tubule gives rise to a polar capsule which houses a helically coiled polar tubule. The apical end of each polar capsule is plugged by a stopper. The valvogenic cells surround the capsulogenic and posteriorly situated sporoplasm cells to form the spore valves. Iodinophilic (glycogen) inclusions were not seen in spores stained with iodine or Best's carmine. A darkly stained band was observed around the posterior region of most spores stained with Best's carmine. In the electron microscope large aggregates of beta glycogen particles were seen in the cytoplasm of sporoplasm cells in mature spores.

Animals↗
PubMed2004

5-fluorouracil vs. beta-irradiation in the prevention of pterygium recurrence.

The aim of this study was to compare 5-fluorouracil (5-FU) with beta-irradiation in the prevention of pterygium recurrence. A retrospective non-randomised review of cases of fleshy pterygium treated with bare scleral excision and adjuvant 5-FU were compared with similar morphologically appearing pterygia, matched for age and sex, treated with bare scleral excision and adjuvant beta-irradiation. All surgeries were carried out at the university college hospital and Ojulowo eye hospital, Ibadan, Nigeria. Twenty-seven eyes of 24 patients who had pterygium excision with adjuvant treatment with 5-FU were compared with 31 eyes of 24 patients who were treated with excision and beta-irradiation. The mean age for the 5-FU group was 46.1 years while that for the beta-irradiation group was 46.9 years. Both sexes were equally represented, 12 males and 12 females. There were seven (25.9%) initial recurrences in the 5-FU group but four of these became atrophic, and therefore, cosmetically acceptable leaving three eyes (11%) with unacceptable recurrent pterygia. The beta-irradiation group, however, had seven (22.5) initial recurrence but five of these became atrophic and fell short of the cornea, leaving two (6.5%) with clinically unacceptable recurrence. The difference was, however, not statistically significant (Zc = 0.74 and p > 0.1). The associated complications were mostly mild in both groups and included cornea opacity of 10 (37%) complications, conjunctivitis of three (11%) complications, sclera granuloma of three (11%) complications and conjunctiva necrosis of one (3.7%) complication for the 5-FU group, and while the beta-irradiation group had corneal opacity of one (3.7%) complication and conjunctivitis of three (11%) complications. The non-statistical significance of a lower-pterigium recurrence rate with use of beta-irradiation for the treatment of fleshy pterygium compared with 5-FU may have been partly due to the small number of patients studied. A randomised-controlled study using a larger sample size is therefore proposed. However, the fact that over half of those with initial recurrence in the 5-FU group became atrophic (and therefore cosmetically acceptable) over time as well as less cost implication in the purchase of 5-FU relative to Strontium-90 association with few and mild complications makes it a desirable adjuvant therapy in depressed economies. However, beta-irradiation still has a place when cost issue is not an inhibiting factor in view of its clinically superior outcome.

Antimetabolites↗
PubMed1984

Working with cathode-ray tube based visual display units.

Eye strain when working with visual display units might be due to bad ergonomics but also to eye functions not meeting the demands. If the symbol on the screen has a 4 mm height and the working distance is 60 cm, a visual acuity of 0.4 is required. However to read with ease in the long run a visual acuity of 0.7 is needed. Therefore the employee's visual acuity and refraction must be examined when newly employed, at the age of forty, then every fifth year and when having problems. Other eye dysfunctions could be revealed from questionnaires.

Asthenopia↗
PubMed2002

Monte Carlo dosimetry of a tandem positioned beta-emitting intravascular brachytherapy source train.

Prevention of restenosis following interventional coronary procedures with catheter based beta-emitting sources is currently under clinical trial investigations. Systems utilizing fixed length source trains limit the clinician's ability to increase the radiation source length as required. A technique known as "pull back" is used when the segment of artery requiring radiation is longer than the available fixed length source train. In this instance, tandem positioning of the fixed length source is used to treat the longer length of artery. The aim of this study was to examine the dosimetry of the junction region associated with pull back treatments using a commercially available 90Sr/Y catheter based intravascular brachytherapy source train. Dose profiles were calculated, using the Monte Carlo code MCNP4B, at radial distances of 1.5, 2.0, and 2.5 mm for pull back techniques using 2.5 mm overlapping, abutting, and 2.5 mm spaced source trains. Results at the protocol prescription radius of 2 mm showed a junction dose elevated 61% above prescription for 2.5 mm overlapping source trains. For 2.5 mm spaced trains, this figure falls to 64% below prescription dose. In contrast, abutted source trains exhibited only a 1% depression below prescription dose in the junction region. The reference point dose rate per unit activity of this source was found to be consistent with previous studies.

Algorithms↗
PubMed2002

Monte Carlo dose calculations in homogeneous media and at interfaces: a comparison between GEPTS, EGSnrc, MCNP, and measurements.

Three Monte Carlo photon/electron transport codes (GEPTS, EGSnrc, and MCNP) are bench-marked against dose measurements in homogeneous (both low- and high-Z) media as well as at interfaces. A brief overview on physical models used by each code for photon and electron (positron) transport is given. Absolute calorimetric dose measurements for 0.5 and 1 MeV electron beams incident on homogeneous and multilayer media are compared with the predictions of the three codes. Comparison with dose measurements in two-layer media exposed to a 60Co gamma source is also performed. In addition, comparisons between the codes (including the EGS4 code) are done for (a) 0.05 to 10 MeV electron beams and positron point sources in lead, (b) high-energy photons (10 and 20 MeV) irradiating a multilayer phantom (water/steel/air), and (c) simulation of a 90Sr/90Y brachytherapy source. A good agreement is observed between the calorimetric electron dose measurements and predictions of GEPTS and EGSnrc in both homogeneous and multilayer media. MCNP outputs are found to be dependent on the energy-indexing method (Default/ITS style). This dependence is significant in homogeneous media as well as at interfaces. MCNP(ITS) fits more closely the experimental data than MCNP(DEF), except for the case of Be. At low energy (0.05 and 0.1 MeV), MCNP(ITS) dose distributions in lead show higher maximums in comparison with GEPTS and EGSnrc. EGS4 produces too penetrating electron-dose distributions in high-Z media, especially at low energy (<0.1 MeV). For positrons, differences between GEPTS and EGSnrc are observed in lead because GEPTS distinguishes positrons from electrons for both elastic multiple scattering and bremsstrahlung emission models. For the 60Co source, a quite good agreement between calculations and measurements is observed with regards to the experimental uncertainty. For the other cases (10 and 20 MeV photon sources and the 90Sr/90Y beta source), a good agreement is found between the three codes. In conclusion, differences between GEPTS and EGSnrc results are found to be very small for almost all media and energies studied. MCNP results depend significantly on the electron energy-indexing method.

Algorithms↗
PubMed2003

Beta voxel S values for internal emitter dosimetry.

Monte Carlo volume integration of dose point kernels was used for calculating voxel S values of beta emissions of radionuclides of interest for internal radiotherapy. The method was verified by comparing our results with others derived from Monte Carlo radiation transport simulation. The algorithm has been implemented in a C++ program that can be used by any laboratory to calculate voxel S values of beta emissions from tabulated dose point kernels and for any combination of pixel edges and the thickness of SPECT and PET images without the complexity and expertise needed for direct Monte Carlo radiation transport simulations.

Algorithms↗