Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 48
Filtrar
Mais filtros

Base de dados
Tipo de documento
Intervalo de ano de publicação
1.
Histochem Cell Biol ; 132(1): 83-93, 2009 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-19319559

RESUMO

Merkel cells (MCs) are neuroendocrine cells of unknown origin located in the skin. They are identified at electron microscopic level by electron dense granules, at light microscopic level by the presence of cytokeratins 8, 18, 19 and 20. Contradictory reports concerning the presence of other molecules of epithelial as well as neural origin prompted us to investigate whether there are distinct populations of human MCs. Here, we show the heterogeneous expression of villin, N-CAM, NGF-R, and neurofilaments in MCs. Synaptophysin is found in all MCs but with different intensity, nestin is absent. Expression patterns vary between interfollicular epidermis, hair follicles and glabrous epidermis. We conclude that there are distinct populations of MCs, but all populations contain markers for epithelial as well as neural cells. Putative functions of the distinct populations are discussed.


Assuntos
Células de Merkel/citologia , Antígenos de Diferenciação/metabolismo , Linhagem da Célula , Células Epidérmicas , Epiderme/metabolismo , Folículo Piloso/citologia , Folículo Piloso/metabolismo , Humanos , Imuno-Histoquímica , Filamentos Intermediários/metabolismo , Células de Merkel/metabolismo , Células Neuroendócrinas/citologia , Células Neuroendócrinas/metabolismo
2.
Perspect Psychol Sci ; 12(3): 527-542, 2017 05.
Artigo em Inglês | MEDLINE | ID: mdl-28475467

RESUMO

In an anonymous 4-person economic game, participants contributed more money to a common project (i.e., cooperated) when required to decide quickly than when forced to delay their decision (Rand, Greene & Nowak, 2012), a pattern consistent with the social heuristics hypothesis proposed by Rand and colleagues. The results of studies using time pressure have been mixed, with some replication attempts observing similar patterns (e.g., Rand et al., 2014) and others observing null effects (e.g., Tinghög et al., 2013; Verkoeijen & Bouwmeester, 2014). This Registered Replication Report (RRR) assessed the size and variability of the effect of time pressure on cooperative decisions by combining 21 separate, preregistered replications of the critical conditions from Study 7 of the original article (Rand et al., 2012). The primary planned analysis used data from all participants who were randomly assigned to conditions and who met the protocol inclusion criteria (an intent-to-treat approach that included the 65.9% of participants in the time-pressure condition and 7.5% in the forced-delay condition who did not adhere to the time constraints), and we observed a difference in contributions of -0.37 percentage points compared with an 8.6 percentage point difference calculated from the original data. Analyzing the data as the original article did, including data only for participants who complied with the time constraints, the RRR observed a 10.37 percentage point difference in contributions compared with a 15.31 percentage point difference in the original study. In combination, the results of the intent-to-treat analysis and the compliant-only analysis are consistent with the presence of selection biases and the absence of a causal effect of time pressure on cooperation.


Assuntos
Comportamento Cooperativo , Heurística , Relações Interpessoais , Tomada de Decisões , Humanos , Intenção , Modelos Psicológicos
3.
Cancer Res ; 53(5): 1091-7, 1993 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-8439953

RESUMO

The antitumor activity of cis-diamminedichloroplatinum(II) (cP) and human recombinant interleukin-1 alpha (IL-1 alpha) was studied in RIF-1 and SC VII solid tumor models and in a cP-resistant subline of RIF-1 designated RIF-R1cP. In RIF-1 tumors, clonogenic cell survival after cP plus IL-1 alpha combinations was highly schedule and IL-1 alpha dose dependent. More than additive clonogenic cell kill was seen when cP was given 6 h before, but not 8 h before or at 2-6 h after IL-1 alpha. Time course studies indicated that maximal clonogenic cell killing was achieved within 4-6 h after the cP plus IL-1 alpha combination, with little or no recovery for up to 24 h. In vivo dose-response studies indicated that cP plus IL-1 alpha combinations induced more clonogenic cell kill than cP alone in all three tumor models, and analysis by the median effect principle indicated highly synergistic antitumor activity. Dexamethasone but not indomethacin inhibited the synergistic interaction. IL-1 alpha had no effect on the cytotoxicity of cP in SCC VII cells in vitro, and neither in vitro hypoxia nor in vivo ischemia, induced by clamping tumor blood supply, significantly affected cP clonogenic cell killing. Increased clonogenic cell killing was seen, however, after removal of the clamp, implicating reperfusion events, such as oxyradical stress, as a potential mechanism for increased cP cytotoxicity in SCC VII solid tumors. The data from our model systems provide a rationale for additional work to define the mechanisms of the synergistic antitumor activity of the cP plus IL-1 alpha combination and indicate that IL-1 alpha might be a useful adjunct to increase the clinical efficacy of cP-containing strategies for both sensitive and cP-resistant cancers.


Assuntos
Cisplatino/administração & dosagem , Interleucina-1/administração & dosagem , Neoplasias Experimentais/tratamento farmacológico , Animais , Sobrevivência Celular/efeitos dos fármacos , Cisplatino/farmacologia , Relação Dose-Resposta a Droga , Resistência a Medicamentos , Sinergismo Farmacológico , Feminino , Interleucina-1/farmacologia , Camundongos , Camundongos Endogâmicos C3H , Neoplasias Experimentais/patologia , Proteínas Recombinantes/administração & dosagem , Células Tumorais Cultivadas/efeitos dos fármacos
4.
J Invest Dermatol ; 111(2): 251-8, 1998 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-9699726

RESUMO

Few data are available on early regeneration of human epidermis in vivo. We have established a supravital skin organ culture model for epidermal wound healing by setting a central defect (3 mm diameter) in freshly excised skin specimens and culturing under air exposure. Re-epithelialization was followed for up to 7 d by histology and immunohistologic analysis of various markers for differentiation and proliferation. In 12 of 19 cases (63%; 5% fetal calf serum) or six of 21 cases (29%; 2% fetal calf serum), the wounds were re-epithelialized spontaneously after 7 d. After transplantation to the wounds of 1-2 x 10(6) dissociated allogenic cultured epidermal or about 1 x 10(6) autologous outer root sheath keratinocytes, 18 of 21 cases (86%; 5% fetal calf serum) or 17 of 21 cases (81%; 2% fetal calf serum) were healed within the same period. Histologically, early neoepithelium (3 d) was disordered after keratinocyte transplantation, whereas later (7 d) it had gained a more ordered stratification, exhibiting a thin discontinuous granular and a compact horny layer. At this stage, not only hyperproliferative (CK 6) but also, abundantly, maturation-associated cytokeratins (CK 1, CK 10) were detected immunohistochemically. Analyses of regenerated epidermis after transplantation of (i) keratinocytes labeled in vitro with BrdU and (ii) heterosexual keratinocytes by immunohistochemistry and fluorescence in situ hybridization for the Y chromosome, respectively, clearly showed that external keratinocytes are physically integrated into the regenerated epidermis and extendedly contribute to its formation. The data presented here demonstrate improvement and acceleration of epidermal re-epithelialization by transplantation of keratinocytes.


Assuntos
Epiderme/fisiologia , Queratinócitos/fisiologia , Cicatrização , Adolescente , Adulto , Divisão Celular , Feminino , Humanos , Queratinócitos/transplante , Queratinas/análise , Masculino , Pessoa de Meia-Idade , Técnicas de Cultura de Órgãos , Regeneração
5.
Int J Radiat Oncol Biol Phys ; 30(4): 985-92, 1994 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-7961003

RESUMO

PURPOSE: Solid state diodes and/or thermoluminescent dosimeters (TLDs) are often used to measure scattered radiation doses to critical organs immediately adjacent to radiation field sites. The energy-dependent response of these commonly used in vivo dosimeters sometimes makes the interpretation of measured values uncertain. This study investigates scattered radiation arising from the collimator jaws of linear accelerators and the treatment head of a cobalt-60 teletherapy unit. METHODS AND MATERIALS: A thin window Markus-type parallel-plate ionization chamber placed in a polystyrene phantom was employed to document the magnitude, energy composition, and sources of scattered radiation at surfaces near radiation fields. Measurements were taken both with and without additional phantom material covering the ionization chamber, as well as with various distances between the ionization chamber and edges of the radiation fields tested. RESULTS: Data was collected, analyzed and compared for treatment units produced by different manufacturers. It was found that the magnitude of scattered radiation to surfaces immediately adjacent to radiation fields ranged from 1% to 15% of the maximum dose along the beam central axis. These values showed a strong dependence upon distance from the edge of the radiation field, beam energy, collimator setting (field size), and the presence of externally mounted accessories. Teletherapy unit differences due to manufacturing firm origins were found to only slightly affect scattered radiation magnitude, while the orientation of upper and lower collimator jaws had absolutely no effect. CONCLUSIONS: Percent depth dose curves of scattered radiation were obtained and analyzed. The shapes of these depth dose curves suggest the presence of complex energy spectra from secondary electrons and scattered x-rays. Because of the presence of these complex energy spectra in areas immediately adjacent to radiation fields, caution should be observed when interpreting patient doses near radiation fields, if dose values have been measured in vivo using thermoluminescent dosimeters (TLDs) or solid state diodes. Many of these on-patient dosimetry devices are strongly energy dependent and may demonstrate large over- or under-responses in areas dominated by scattered radiation. The results of this study, thus, suggest that ionization chambers are preferred for determination of scattered radiation doses in such regions.


Assuntos
Aceleradores de Partículas , Planejamento da Radioterapia Assistida por Computador , Espalhamento de Radiação , Humanos , Processamento de Sinais Assistido por Computador , Análise Espectral/métodos
6.
Int J Radiat Oncol Biol Phys ; 24(4): 777-80, 1992.
Artigo em Inglês | MEDLINE | ID: mdl-1429104

RESUMO

Stereotactic radiosurgery with a linear accelerator requires an accurate match of the therapeutic radiation distribution to the localized target volume. Techniques for localization of the target volume using CT scans and/or angiograms have been described. Alignment of the therapeutic radiation distribution to the intended point in stereotactic space is usually accomplished using precision mechanical scales which attach to the head ring. The present work describes a technique used to verify that the stereotactic coordinates of the center of the intended radiation distribution are in agreement with the localized target point coordinates. This technique uses anterior/posterior and lateral accelerator portal verification films to localize the stereotactic coordinates of the center of the radiation distribution with the patient in the treatment position. The results of 26 cases have been analyzed. Alignment errors of the therapeutic radiation distribution in excess of 1 mm have been found using the portal film verification procedure.


Assuntos
Encéfalo/cirurgia , Garantia da Qualidade dos Cuidados de Saúde , Radiocirurgia , Técnicas Estereotáxicas , Angiografia Cerebral , Humanos , Tomografia Computadorizada por Raios X
7.
Int J Radiat Oncol Biol Phys ; 21(5): 1321-5, 1991 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-1938531

RESUMO

Stereotactic radiosurgery techniques for a linear accelerator typically use circular radiation fields to produce an essentially spherical radiation distribution with a steep dose gradient. Target volumes are frequently irregular in shape, and circular distributions may irradiate normal tissues to high dose as well as the target volume. Improvements to the dose distribution have been made using multiple target points and optimizing the dose per arc to the target. A retrospective review of 20 radiosurgery patients has suggested that the use of elliptically shaped fields may further improve the match of the radiation distribution to the intended target volume. This hypothesis has been verified with film measurements of the radiation distribution obtained using elliptical radiation beam in a head phantom. Reductions of 40% of the high dose volume have been obtained with elliptical fields compared to circular fields without compromising the dose to the target volume.


Assuntos
Radiocirurgia/métodos , Dosagem Radioterapêutica , Humanos , Modelos Estruturais , Estudos Retrospectivos
8.
Int J Radiat Oncol Biol Phys ; 20(3): 517-23, 1991 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-1995537

RESUMO

Stereotactic radiosurgery with a linear accelerator requires the accurate determination of a target volume and an accurate match of the therapeutic radiation dose distribution to the target volume. X ray and CT localizers have been described that are used to define the target volume or target point from angiographic or CT data. To verify the accuracy of these localizers, measurements were made with a target point simulator and an anthropomorphic head phantom. The accuracy of determining a known, high contrast, target point with these localizers was found to be a maximum of +/- 0.5 mm and +/- 1.0 mm for the X ray and CT localizer, respectively. A technique using portal X rays taken with a linear accelerator to verify the target point is also described.


Assuntos
Radioterapia/instrumentação , Técnicas Estereotáxicas/instrumentação , Tomografia Computadorizada por Raios X/instrumentação , Dosagem Radioterapêutica
9.
Int J Radiat Oncol Biol Phys ; 15(1): 213-8, 1988 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-3391817

RESUMO

This paper describes our experience in using the T1 and T2 relaxation times for quantitative evaluation of brain and brain tumor response to radiation therapy. Twenty-two computed T1 and 22 computed T2 images were obtained from 66 routine inversion-recovery and spin-echo magnetic resonance (MR) brain scans. The relaxation times of the brain tissues, determined from the computed images, were examined as a function of the absorbed dose. Statistical evaluation of the results showed no significant difference between the relaxation times of irradiated and not irradiated tissues, including tumor and normal white matter. Influence of the magnetic field strength and imaging techniques on the computed T1 and T2 values was confirmed. We conclude that the relaxation time values, as obtained today using conventional MR scanner and standard software, are not specific enough to warrant a correct assessment of the acute radiation effect on the brain tissues.


Assuntos
Neoplasias Encefálicas/radioterapia , Encéfalo/efeitos da radiação , Imageamento por Ressonância Magnética , Adolescente , Adulto , Criança , Humanos , Pessoa de Meia-Idade
10.
Int J Radiat Oncol Biol Phys ; 24(4): 795-801, 1992.
Artigo em Inglês | MEDLINE | ID: mdl-1429107

RESUMO

Although high dose-rate brachytherapy with a single, rapidly moving radiation source is becoming a common treatment modality, a suitable formalism for determination of the dose delivered by a moving radiation source has not yet been developed. At present, brachytherapy software simulates high dose-rate treatments using only a series of stationary sources, and consequently fails to account for the dose component delivered while the source is in motion. We now describe a practical model for determination of the true, total dose administered. The algorithm calculates both the dose delivered while the source is in motion within and outside of the implanted volume (dynamic component), and the dose delivered while the source is stationary at a series of fixed dwell points. It is shown that the dynamic dose element cannot be ignored because it always increases the dose at the prescription points and, in addition, distorts the dose distribution within and outside of the irradiated volume. Failure to account for the dynamic dose component results in dosimetric errors that range from significant (> 10%) to negligible (< 1%), depending on the prescribed dose, source activity, and source speed as defined by the implant geometry.


Assuntos
Braquiterapia/métodos , Planejamento da Radioterapia Assistida por Computador , Humanos , Doses de Radiação
11.
Int J Radiat Oncol Biol Phys ; 21(6): 1621-5, 1991 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-1938572

RESUMO

Computer controlled high dose-rate (HDR) brachytherapy afterloading machines are equipped with a single, miniaturized, high activity Ir-192 source that can be rapidly moved in fine increments among several channels. Consequently, by appropriate programming of source dwell positions and times, the dose distribution can be optimized as desired. We have explored the optimization potential of this new technology for two applications: (a) cervix brachytherapy, and (b) transvaginal irradiation. Cervix brachytherapy with a gynecologic ring applicator was simulated by 48 sources of relative activities ranging from 0.17 to 1.00 that were equally distributed between the tandem and the ring. The results confirmed that the optimized distribution of physical doses are superior to those achievable with standard brachytherapy sources and applicators. For example, with five-point optimization, the relative dose-rate in the rectum was only 47% of that in point A; for standard application the dose rate was 47% higher. For transvaginal application 27 sources of relative activities between 0.07-0.79 were placed in the ring and a single source of unit strength in the tandem. Using dose distribution homogeneity as an optimization criterion, the results (+/- 2.5%) were again superior to those obtained for commonly used double ovoid (+/- 15%), linear cylinder (+/- 27%), or a "T" source (31%).


Assuntos
Braquiterapia , Colo do Útero , Dosagem Radioterapêutica , Planejamento da Radioterapia Assistida por Computador , Radioterapia de Alta Energia , Vagina , Feminino , Humanos
12.
Int J Radiat Oncol Biol Phys ; 17(5): 1111-4, 1989 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-2808046

RESUMO

Spatial definition of an intraocular tumor and subsequent determination of the actual position of an implanted eye plaque are essential for adequate ocular brachytherapy treatment planning. However, a method for verification of the plaque placement which would provide required 3-dimensional information is not available at present. In addition, tumor localization procedures, including ultrasonography and CT techniques, cannot always offer the precision needed for 3-dimensional definition of an intraocular target. This communication describes a magnetic resonance imaging technique specifically developed for both localization and verification procedures. A 1.5 Tesla magnetic resonance scanner, spin-echo pulse sequence (echo time 30 msec, repetition time 700 msec), and commercially available surface coil were used to obtain a series of transverse, coronal, and sagittal images of a slice thickness of 3 mm. Usually, eight scans in each of the three planes were needed for adequate coverage of the orbit. The required patient set-up and data acquisition time did not exceed 40 minutes. With a data matrix size of 256 X 256 pixels and 13 cm field of view, localization and verification were accomplished with a precision of 0.5 mm. Our results suggest that the magnetic resonance imaging technique permits precise integration of diagnostic and therapeutic procedures, and in addition provides adequate data for accurate treatment planning. We conclude that magnetic resonance imaging is the preferred diagnostic technique for episcleral brachytherapy.


Assuntos
Braquiterapia/métodos , Neoplasias Oculares/radioterapia , Melanoma/radioterapia , Humanos , Imageamento por Ressonância Magnética , Esclera
13.
Int J Radiat Oncol Biol Phys ; 22(1): 175-80, 1992.
Artigo em Inglês | MEDLINE | ID: mdl-1727115

RESUMO

A computer-controlled stereotaxic radiotherapy system based on a low-frequency magnetic field technology integrated with a single fixation point stereotaxic guide has been designed and instituted. The magnetic field, generated in space by a special field source located in the accelerator gantry, is digitized in real time by a field sensor that is six degree-of-freedom measurement device. As this sensor is an integral part of the patient stereotaxic halo, the patient position (x, y, z) and orientation (azimuth, elevation, roll) within the accelerator frame of reference are always known. Six parameters--three coordinates and three Euler space angles--are continuously transmitted to a computer where they are analyzed and compared with the stereotaxic parameters of the target point. Hence, the system facilitates rapid and accurate patient set-up for stereotaxic treatment as well as monitoring of patient during the subsequent irradiation session. The stereotaxic system has been developed to promote the integration of diagnostic and therapeutic procedures, with the specific aim of integrating CT and/or MR aided tumor localization and long term (4- to 7-week) fractionated radiotherapy of small intracranial and ocular lesions.


Assuntos
Radioterapia Assistida por Computador/métodos , Técnicas Estereotáxicas , Fenômenos Eletromagnéticos , Humanos , Planejamento da Radioterapia Assistida por Computador
14.
Radiat Res ; 145(2): 150-6, 1996 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-8606924

RESUMO

Interleukin-1 (IL-1) has radioprotective activity in hematopoietic lineages and in other normal cell renewal systems, but little is known about the effects of IL-1 alpha on the radiosensitivity of tumor cell populations. The present studies were conducted to investigate the effects of IL-1 alpha on the radiosensitivity of clonogenic cells in RIF-1 and SCC-7 tumors. Radioresistance was detected within 2-4 after administration of IL-1 alpha (0.5 micrograms/mouse, ip) and characterized by increases in D(o), Dq, alpha/beta and SF2. This radioresistance was similar to that seen in tumors rendered totally hypoxic before X irradiation. Tirapazamine, a hypoxic cell cytotoxin, and IL-1 alpha had synergistic schedule-dependent antitumor activity in vivo, suggesting that IL-1-induced radioresistance in vivo is due to hypoxia. Radioresistance induced by IL-1 alpha was transient, and the data suggested reoxygenation within 12 h. In vitro, IL-1 alpha had no direct effect on the radiosensitivity of SCC-7 cells in tissue culture under aerobic conditions. However, an increase in D(o), alpha/beta and SF2 was seen in clonogenic tumor cells from primary cultures treated with IL-1 alpha under aerobic conditions. Superoxide dismutase and catalase prevented the induction of radioresistance by IL-1 alpha in vitro, suggesting that oxidative responses from tumor macrophages after administration of IL-1 alpha may be responsible for induced radioresistance by IL-1 in vitro. Although oxidant stress induced by IL-1 and in vitro in our models, the mechanisms by which such responses modulate tumor radiosensitivity in vivo and in vitro are likely quite different.


Assuntos
Interleucina-1/administração & dosagem , Interleucina-1/farmacologia , Protetores contra Radiação/administração & dosagem , Radiossensibilizantes/administração & dosagem , Animais , Catalase/metabolismo , Sobrevivência Celular/efeitos da radiação , Células Clonais , Sinergismo Farmacológico , Hipóxia/metabolismo , Camundongos , Neoplasias Experimentais/radioterapia , Lesões Experimentais por Radiação , Proteínas Recombinantes , Superóxido Dismutase/metabolismo , Tirapazamina , Triazinas/administração & dosagem , Células Tumorais Cultivadas/efeitos da radiação , Irradiação Corporal Total
15.
Arch Dermatol ; 111(3): 328-30, 1975 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-1119832

RESUMO

Blood flow in normal skin and skin treated with ultraviolet light (UVL) has been determined by measuring the clearance of epicutaneously applied xenon 133 gas. Mean blood flow in UVL-irradiated skin was 25.7 ml/100 gm/min, which is about twice that found in normal skin (12.2 ml/100 gm/min). Orally administered indomethacin reduced by one third the increase in blood flow produced by UVL irradiation.


Assuntos
Circulação Sanguínea/efeitos da radiação , Indometacina/administração & dosagem , Pele/irrigação sanguínea , Raios Ultravioleta , Circulação Sanguínea/efeitos dos fármacos , Humanos , Indometacina/farmacologia , Placebos , Radioisótopos , Fluxo Sanguíneo Regional/efeitos dos fármacos , Fluxo Sanguíneo Regional/efeitos da radiação , Xenônio
16.
Med Phys ; 10(3): 333-6, 1983.
Artigo em Inglês | MEDLINE | ID: mdl-6410163

RESUMO

Dosimetry for 10-MV x rays has been extended to radiation fields smaller than 4 X 4 cm which may be suitable for radiation therapy of small lesions, e.g., intracranial tumors, benign or malignant. Special consideration in this study was given to (i) the variation of dose with field size (collimator and phantom scatter), (ii) the central axis percentage depth doses, and (iii) the moving-beam therapy dose distribution. We conclude that simple dosimetric techniques can provide adequate physics background for stereotaxic radiosurgery with small radiation fields and high-energy x rays.


Assuntos
Doses de Radiação , Radioterapia de Alta Energia/métodos , Neoplasias Encefálicas/radioterapia , Aceleradores de Partículas , Espalhamento de Radiação , Técnicas Estereotáxicas
17.
Med Phys ; 12(4): 469-72, 1985.
Artigo em Inglês | MEDLINE | ID: mdl-3929051

RESUMO

A stereotaxic radiotherapy technique that permits accurate delivery of highly localized dose to a small intracranial target has been developed. The technique facilitates precise integration of the diagnostic and therapeutic procedures including target localization, treatment planning, simulation, repetitive patient irradiation, and daily treatment verification. A conventional linear accelerator and computed tomography scanner as well as special diagnostic and therapeutic guides are used. A suitable dosimetric distribution is achieved using arc therapy with small radiation fields and 10-MV x rays.


Assuntos
Neoplasias Encefálicas/radioterapia , Radioterapia de Alta Energia/métodos , Técnicas Estereotáxicas , Fenômenos Biofísicos , Biofísica , Neoplasias Encefálicas/diagnóstico por imagem , Humanos , Modelos Estruturais , Dosagem Radioterapêutica , Tomografia Computadorizada por Raios X
18.
Med Phys ; 18(6): 1266-70, 1991.
Artigo em Inglês | MEDLINE | ID: mdl-1753916

RESUMO

Dosimetry calculations for iridium-192 sources generally assume that a sufficient medium surrounds both the iridium source(s) and the point of calculation so that full scattering conditions exist. In several clinical applications the iridium sources may be anatomically located so that the full scattering requirement is not satisfied. To assess the magnitude of this problem, relative measurements were made with a small ionization chamber in phantoms near air and lung-equivalent interfaces. Dose reduction caused by decreasing the volume of scattering material near these interfaces was then evaluated for a few clinical applications. The results show that reductions on the order of 8% may be expected at the interface with minimal dose reduction within the volume of the implant itself. In addition, the results indicate the verification of source strength of iridium sources in phantom require phantom dimensions determined by the source-chamber separation distance.


Assuntos
Braquiterapia , Radioisótopos de Irídio/uso terapêutico , Radiometria/métodos , Dosagem Radioterapêutica , Humanos , Modelos Estruturais , Radiometria/instrumentação , Espalhamento de Radiação
19.
Med Phys ; 19(1): 181-5, 1992.
Artigo em Inglês | MEDLINE | ID: mdl-1620045

RESUMO

Stereotactic radiosurgery of the brain may be accomplished with a linear accelerator by performing several noncoplanar arcs of a highly collimated beam focused at a point. The shape of the radiation distribution produced by this technique is affected by the beam energy, field size, and the number and size of the arcs. The influence of these parameters on the resulting radiation distributions was analyzed by computing dose volume histograms for a typical brain. Dose volume functions were computed for: (a) the energy range of 4-24 MV x rays; (b) target sizes of 1-4 cm; and (c) 1-11 arcs and dynamic rotation. The dose volume histograms were found to be dependent on the number of arcs for target sizes of 1-4 cm. However, these differences were minimal for techniques with 4 arcs or more. The influence of beam energy on the dose volume histogram was also found to be minimal.


Assuntos
Radiocirurgia/métodos , Planejamento da Radioterapia Assistida por Computador/métodos , Encéfalo/anatomia & histologia , Humanos , Aceleradores de Partículas
20.
Med Phys ; 19(6): 1451-3, 1992.
Artigo em Inglês | MEDLINE | ID: mdl-1461209

RESUMO

Assessment of electron beam energy and its long term stability is part of standard quality assurance practice in radiation oncology. Conventional depth-ionization or depth-film density measurements are time consuming both in terms of data acquisition and analysis. A procedure is described utilizing ionization measurements at two energy specific depths. It is based on a linear relationship between electron beam energy and its practical range. Energy shifts within the range covered by the two measurement depths are easily resolved. Within a range of +/- 0.50 MeV (+/- 1.30 MeV) around the established mean incident energy of 5.48 MeV (20.39 MeV), the method accuracy is better than 0.10 MeV.


Assuntos
Elétrons , Aceleradores de Partículas , Radioterapia de Alta Energia/normas , Humanos
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA