Perfil de uso de tigeciclina en un hospital universitario en Chile / Profile of tigecycline use in a university hospital in Chile

INTRODUCCIÓN: El uso de tigeciclina ha ido en aumento en los últimos años, debido al incremento de la resistencia bacteriana y la escasez de alternativas terapéuticas. OBJETIVO: Caracterizar y evaluar las prescripciones de tigeciclina en pacientes internados en un hospital universitario, durante los años 2017 y 2018. METODOLOGÍA: Estudio observacional retrospectivo, donde se caracterizaron los pacientes, las terapias, la microbiología asociada, los desenlaces clínicos y las reacciones adversas asociadas a los tratamientos con tigeciclina. Se determinó la proporción de prescripciones apropiadas por un comité de expertos y el consumo de tigeciclina medido en DDD/100 camas-día. RESULTADOS: Se caracterizaron 89 pacientes, de los cuales 67 (75,3%) cumplieron los criterios de selección. El 53,7% de los pacientes eran hombres, con una edad promedio de 60 ± 15 años. El principal motivo de hospitalización fue quirúrgico (65,7%). El 67,1% de los tratamientos con tigeciclina se inició en una Unidad de Paciente Critico y el foco de infección predominante fue abdominal (64,3%). El 50% de las terapias con tigeciclina fueron dirigidas según la microbiología identificada. En 65,7% de los casos se usó tigeciclina como monoterapia en la dosis habitual (62,9%). Náuseas (8,6%), diarrea (7,1%) y vómitos (4,3%) fueron los efectos adversos más reportados. El 84,3% de los tratamientos se consideraron apropiados. El año 2017 se consumió 0,4 DDD/100 camas-día y 0,6 DDD/100 camas/día el 2018, siendo la UCI el servicio que presentó el mayor uso en ambos años. DISCUSIÓN: Tigeciclina fue utilizada principalmente en monoterapia para el tratamiento de infecciones intraabdominales en pacientes hospitalizados, por motivos quirúrgicos, en una unidad de paciente crítico, en las dosis habituales recomendadas de 100 mg como dosis de carga seguida de 50 mg cada 12 hs IV. En 50% de los casos, la terapia fue dirigida según microbiología. Los eventos adversos más habituales fueron los gastrointestinales. CONCLUSIÓN: La mayoría de las terapias prescritas fueron consideradas apropiadas por el comité de expertos.

BACKGROUND: The use of tigecycline has been increasing in recent years, due to increase in bacterial resistance and the scarcity of therapeutics alternatives. AIM: To characterize and evaluate the tigecycline prescriptions of patients hospitalized in a university hospital, during the years 2017 and 2018. METHODS: A retrospective observational study was carried out, where the patients, the therapies, the associated microbiology, the clinical outcomes and the adverse reactions associated with tigecycline were characterized. The proportion of appropriate prescriptions was determined by committee of experts and the consumption of tigecycline measure in DDD/100 bed-days. RESULTS: 89 patients who used tigecycline were characterized, of which 67 (75.3%) met the selection criteria. 53.7% of the patients were male, with a mean age of 60 +/- 15 years The main reason for hospitalization was surgical (65.7%). 67.1% of the treatments with tigecycline were started in a critical patient unit and the predominant focus of the infection was the abdomen (64.3%). 50% of the therapies with tigecycline were ordered according to the identified microbiology. In 65.7% of the cases, tigecyclin was used as monotherapy at the usual dose (62.9%). Nausea (8.6%), diarrhea (7.1%) and vomiting (4.3%) were the most reported adverse events. 84.3% of the treatments were considered appropriate. In 2017, 0.4 DDD/100 bed/days were consumed and 0.6 DDD/100 bed/days in 2018, with de ICU being the service that presented the highest use in both years. DISCUSSION: Tigecycline was mainly used as monotherapy for the treatment of intra-abdominal infections in patients hospitalized for surgical reasons in a critical patient unit at the usual doses of 100 mg loading followed by 50 mg every 12 hours IV. In 50% of the case the therapy was directed according to microbiology. The most common adverse events were gastrointestinal. CONCLUSION: Most of the prescribed therapies were considered appropriate by the expert committee.

Synthesis, characterization and thermoluminescence properties of MgB4O7 phosphor co-doped with Tm and Dy.

The luminescent and dosimetric properties of the MgB4O7 phosphor co-doped with Tm and Dy ions (MgB4O7:Tm,Dy) obtained by the solution combustion technique were investigated. With the prepared material, sintered dosimeters in pellet form were made. The MgB4O7 dosimeters doped with Tm and Dy with 0.25 and 0.10 mol% respectively and sintered at 1223 K for 3 h showed a sensitivity almost 11 times greater than the sensitivity of the TLD-100 commercial dosimeter. The TL response as a function of the gamma dose showed linearity up to 50 Gy followed by a supralinearity region and, above 500 Gy, the saturation region of the electron traps is reached. The fading of the main TL peak was negligible in the first five days after irradiation reaching 13% after 60 days and the lower detection limit was 43 µGy. The kinetic parameters were determined using the deconvolution method revealing general and second order kinetics. The morphology, crystallography and photoluminescence of the prepared phosphor samples are also reported.

Caracterización de la utilización de colistín en un hospital de alta complejidad / Evaluation of colistin use in a highly complex hospital

RESUMEN: El aumento de la resistencia y la escasez de nuevos antibacterianos ha requerido la reintroducción de antiguos antimicrobianos entre ellos colistín. OBJETIVO: Caracterizar la utilización de colistín durante el año 2017 en un hospital universitario, mediante la descripción de los pacientes, los tratamientos, la microbiología asociada y efectos adversos. PACIENTES Y MÉTODOS: Trabajo observacional retrospectivo. Se revisaron los datos de todos los pacientes que recibieron colistín intravenoso (IV) por al menos 48 horas, durante el año 2017. RESULTADOS: Se incluyeron 53 pacientes, equivalentes a 91 tratamientos. El foco respiratorio fue el principal (46,2%). El 68,1% de los tratamientos fue iniciado en la UCI. La mayoría de los pacientes tenía una hospitalización reciente (83,5%), y presentaban uso previo de antibacterianos (89%). Los dos patógenos mayoritariamente identificados fueron Pseudomonas aeruginosa y Klebsiella spp. El consumo promedio de colistín fue de 2,4 DDD/100 camas/día. El servicio que más consumió colistín fue la UCI, con 45,5 DDD/100 camas/día, usando generalmente la dosis de 3 MUI cada 8 horas IV y con una baja utilización de dosis de carga. CONCLUSIÓN: Colistín corresponde a un antimicrobiano de uso restringido a infecciones sospechadas o confirmadas por agentes bacterianos multi resistentes. En esta serie, su uso inicial fue principalmente empírico, en pacientes con factores de riesgo para resistencia antibacteriana; se usó en forma asociada a otros antimicrobianos, siendo el foco principal el respiratorio.

BACKGROUND: The increase in resistance and the shortage of new antibiotics has led to the reintroduction of old antimicrobials such as colistin. AIM: To evaluate the use of colistin during 2017 in a university hospital, through the characterization of patients and treatment, associated microbiology, response to treatment and adverse effects. METHODS: Retrospective observational design. The data of all patients who received colistin for at least 48 hours during the year 2017 were reviewed. RESULTS: 55 patients were included, equivalent to 144 treatments. The respiratory focus was the main one (57.9%). 64% of the treatments began in the ICU, while 7% in the ward. Most of the patients has a recent hospitalization (86.8%) and has previous use of antibiotics (90.4%). The two main pathogens identified were Pseudomonas aeruginosa and Klebsiella spp. In 87.1% of the cases with microbiological justifications for the use of colistin, a favorable response was obtained. The average consumption of colistin was 2.4 DDD/100 beds/day. The department that consumed the most colistin was the ICU, with 45,5 DDD/100 beds/day, generally using a dose of 3 MIU every 8 hours IV and with low use of loading doses. CONCLUSION: Colistin corresponds to an antibiotic whose use is restricted to infections suspected or confirmed by multi-resistant bacterial agents. Its initial use in this serie was mainly empirical, in patients with risk factors for antibiotics resistance, it was used in association with other antimicrobials, being the respiratory the main infectious focus.

A comprehensive approach using multiple biomarkers to detect damage induced by pesticides in broad-snouted caiman (Caiman latirostris) under ex-situ conditions.

Caiman latirostris is one of the two species of the order Crocodylia that inhabit Argentina and is considered a species of vital ecological and economic importance in the north-east of Argentina. In this region, pesticides are the most common contaminants in natural environments and wild caiman populations are subject to this contamination constantly. The aim of this study was to evaluate the effects the main pesticides used in the region: glyphosate (GLY), cypermethrin (CYP) and chlorpyrifos (CPF) -based formulations, as well as the mixture of them, on C. latirostris juveniles under semi-controlled condition of exposure (ex-situ) during 75 days. One hundred yearling caimans (10-month-old) were equally distributed into five experimental groups (20 animals per group): a negative control (NC -tap water), GLY 2% (Roundup® Full II formulation -RU), CYP 0.12% (Atanor® formulation), CPF 0.8% (Lorsban® formulation), and a mixture of the three pesticides (Mx3: GLY 2% + CYP 0.12% + CPF 0.8%). We applied early warning biomarkers to detect damage induced by these chemicals in peripheral blood: activity of the antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD), analysis of lipid peroxidation (LPO) by the thiobarbituric acid reactive substances (TBARS), DNA damage and specific base oxidation through the standard and modified comet assay (CA), chromosome damage by micronucleus (MN) test and other nuclear abnormalities (NAs), hematological and growth parameters. Results showed a statistically significant increase in MN and NAs frequency, DNA damage, with an important contribution of base oxidation for all exposed groups compared to the NC. Total white blood cells count (TWBCC), and growth parameters showed effects mainly at the Mx3. The principal component analysis (PCA) demonstrated more sensitivity for biomarkers associated to genetic damage, including base oxidation to DNA than LPO, antioxidant enzyme modulation, immunotoxicity or growth parameters, to detect pesticides effects, applied under conditions similar to that found in natural environments.

Luminescence and kinetics parameters of high sensitivity MgB4O7 phosphor co-doped with Tm and Dy.

This work reports the luminescence and kinetics parameters of high sensitivity MgB4O7 phosphor co-doped with Tm and Dy ions (MgB4O7:Tm,Dy) obtained by the solution combustion technique. With the obtained material, sintered dosimeters in form of discs were made and subjected to 1223 K for 3 h and exposed to gamma radiation from a60Co source. It was found that these dosimeters show a sensitivity approximately 10 times higher than that shown by the commercial dosimeter TLD-100 (LiF:Mg,Ti). The kinetic parameters from three samples with different concentration of dopants were determined using the initial rise, peak shape and deconvolution methods. Initial rise and peak shape methods showed lower values than those found by the deconvolution method for the main peak (Peak 1). MgB4O7:Tm, Dy shows a wide linearity interval of TL response with respect to gamma dose and low coefficient of variability (1.5%). These results suggest that this new high sensitivity phosphor could be a promising material to be used in clinical dosimetry.

Effect of sintering temperature on sensitivity of MgB4O7:Tm,Ag obtained by the solution combustion method.

Borates are appropriate TL materials for radiation dosimetry, because of their equivalence with tissue. Magnesium borate is a tissue equivalent material and its most important advantage over lithium borate, is that this material is insoluble in water. In this work the effect of sintering temperature on the sensitivity of magnesium borate obtained by the solution combustion technique is presented. The results showed that the material doped with Tm and Ag, subjected to 1223 K, for 3 h, had a sensitivity between two and four times higher than that of the commercial dosimeter TLD-100 making it highly appropriate for applications in clinical dosimetry.

Tirotoxicosis por enfermedad trofoblástica gestacional: revisión a partir de 3 casos / Thyrotoxicosis due to gestational trophoblastic disease: clinical cases

La enfermedad trofoblástica gestacional (ETG) es una complicación del embarazo poco común. Corresponde a un espectro de lesiones proliferativas del tejido trofoblástico: Mola Hidatiforme (MH) en sus formas parcial y completa, Coriocarcinoma, Tumor Trofoblástico y Tumor Trofoblástico Epiteloide. Los distintos tipos de ETG presentan en común la hipersecreción de gonadotrofina coriónica humana (hCG). La hCG es una hormona glicoproteica con una estructura muy similar a la TSH, por lo cual puede estimular la función tiroidea en condiciones fisiológicas y en algunas condiciones patológicas. La ETG puede cursar con hipertiroidismo, el cual puede variar en intensidad, desde una presentación asintomática con alteración leve de hormonas tiroideas a un cuadro de hipertiroidismo manifiesto. Se presentan 3 casos clínicos de pacientes con ETG, específicamente MH que evolucionaron con tirotoxicosis transitoria. Los casos presentaron un cuadro leve de hipertiroidismo con pocos síntomas asociados. La taquicardia fue el único síntoma en la mayoría de los casos. En todas las pacientes las hormonas tiroideas se normalizaron después del tratamiento de la ETG. Conclusión: Se debe tener presente la posibilidad de hipertiroidismo en toda paciente con ETG. Un alto nivel de sospecha permitirá identificar a aquellas pacientes que cursen con hipertiroidismo, permitiendo así un diagnóstico y tratamiento oportuno.

Gestational trophoblastic disease (GTD) is a rare complication of pregnancy. GTD includes a group of proliferative lesions of trophoblastic tissue: partial and complete hydatidiform mole, choriocarcinoma, epithelioid trophoblastic tumor, and placental site trophoblastic tumor. The different types of GTD have in common the hypersecretion of human chorionic gonadotropin (hCG). HCG is a glycoprotein hormone with a similar structure to TSH. In physiological and pathological conditions hCG can stimulate thyroid function. GTD can present with hyperthyroidism, which can vary in intensity, from an asymptomatic presentation with mild alteration of thyroid hormones to a manifest hyperthyroidism. We present 3 clinical cases of patients with GTD thyrotoxicosis. All cases presented mild hyperthyroidism. Tachycardia was the only symptom in most cases. In all patients thyroid hormones return to normal after treatment of GTD. Conclusion: In patients with GTD the possibility of hyperthyroidism should be kept in mind. A high level of suspicion will allow to identifying patients with hyperthyroidism.

Dosimetric properties of Li2B4O7:Cu,Ag,P solid detector.

This work presents results obtained following the preparation of lithium borate by the chemical reaction between lithium carbonate (Li2CO3) and boric acid (H3BO3), doping the host salt of lithium borate (Li2B4O7) with ions of copper, silver and phosphorus. With the obtained material dosimeters were produced in sintered pellet form which were exposed by gamma radiation that emitted from 60Co source. The highest sensitivity was found for the sample of Li2B4O7:Cu,Ag,P (in pellet form) with 0.45, 0.45 and 12 mol% of Cu, Ag and P, respectively, subjected to a thermal treatment at 1123 K during 2 h. The TL response shows linearity in the dose range from 0.005 to 100 Gy. The lower detection limit (LDL) was equal to 6.10 µGy. The fading was found to be 3% in the first ten days and 9% at the end of thirty days. The repeatability of TL measurements for twenty cycles, showed a variability coefficient equal to 4.15%. The glow curve shape of Li2B4O7:Cu,Ag,P sintered pellet shows two peaks with general-kinetics order. This new material could be appropriate for dosimetry in clinical radiation applications.

Hipertiroidismo en personas mayores de 65 años: serie de casos de un hospital universitario / Thyrotoxicosis in the elderly: case series report from a university hospital

Introducción: En Chile en las últimas décadas ha aumentado la población de personas mayores de 65 años. La tirotoxicosis en este grupo está asociada a complicaciones como fibrilación auricular (FA), insuficiencia cardiaca (ICC), osteoporosis y aumento de la mortalidad. En algunos casos puede presentarse con síntomas no específicos, cuadro conocido como hipertiroidismo apático. Objetivos: Evaluar las características clínicas de la tirotoxicosis en personas mayores. Método: Serie de casos retrospectiva. Se analizaron fichas clínicas de pacientes mayores de 65 años con el diagnóstico de tirotoxicosis controlados en nuestro centro entre enero de 2012 y mayo de 2018. Resultados: En el periodo estudiado 54 pacientes fueron diagnosticados de tirotoxicosis. Se excluyen 4 por datos incompletos. El 80% corresponden a mujeres. La mediana de edad fue 71 años (rango 65-94), sin diferencias por género (p=0,61). La etiología más frecuente fue enfermedad de Graves (EG) en 64%, seguido por bocio multinodular hiperfuncionante en 20%, adenoma tóxico en 10% y asociada a fármacos en 6%. De los pacientes con EG, 28% presentó orbitopatía distiroidea (OD) clínicamente evidente. Un 30% se diagnosticó en contexto de baja de peso, deterioro cognitivo o patología cardiovascular, sin presentar síntomas clásicos de hipertiroidismo. Un 16% presentó FA, 14% ICC y 6% fractura osteoporótica. El 28% fue diagnosticado durante una hospitalización o requirió ser hospitalizado durante los meses siguientes. Los mayores de 75 años presentan una mayor probabilidad de hipertiroidismo apático (OR 5,1, IC95% 1,15-22,7 p=0,01). Además, las complicaciones aumentan en mayores de 75 años, encontrándose en este grupo todos los casos de FA. Conclusiones: La etiología más común de tirotoxicosis fue la EG, a diferencia de lo reportado en otras poblaciones. Un número importante de pacientes debutó sin síntomas clásicos de hipertiroidismo, principalmente mayores de 75 años, por lo que se debe tener una alta sospecha en este grupo etario.

Introduction: Hyperthyroidism in the elderly can produce severe complications such as atrial fibrillation (AF), heart failure (CHF) and osteoporosis. In the elderly, thyrotoxicosis may have only nonspecific symptoms, known as apathetic hyperthyroidism. Objective: To evaluate the clinical characteristics of thyrotoxicosis in the elderly. Methods: Retrospective case series. We reviewed clinical records of patients with thyrotoxicosis older than 65 years, between January 2012 and March 2019. Results: During this period, 54 patients were diagnosed with thyrotoxicosis. Four patients were excluded due to incomplete data. 80% were women. The average age was 73 years (range 65-94), without age difference between gender (p=0,61). The most frequent etiology was Graves' disease in 64%. Hyperfunctioning multinodular goiter was confirmed in 20%, toxic adenoma in 10% and drug-associated in 6%. Twenty eight percent of Graves' disease patients had dysthyroid orbitopathy. Thirty percent presented as apathetic hyperthyroidism. Sixteen percent of the patients presented AF, 14% CHF, and 6% osteoporotic fracture. Twenty-eight percent were diagnosed during hospitalization or required hospitalization in the following months. Those older than 75 years had a greater probability of presenting apathetic hyperthyroidism (OR 5.1, 95% CI 1.15- 22.7 p=0.01). Complications increase in this age group, with all cases of AF. Conclusions: The most common etiology of thyrotoxicosis in this group was GD. This differs from other populations. A significant number of patients presented without classic symptoms of hyperthyroidism, especially in people older than 75 years. Special attention should be paid to atypical symptoms of hyperthyroidism in this group.

Dosimetry in a mammography phantom using TLD-300 dosimeters.

PURPOSE: The purpose of this study was to evaluate the photon field effective energy (Eeff ) distribution and percentage depth-dose (PDD) within a mammography phantom by the analysis of the CaF2 :Tm (TLD-300) thermoluminescent (TL) glow curve. The experimental procedure involves the use of TLD-300 to determine with single dosimeter exposures both the relative dose and the beam quality. METHODS: TLD-300 chips were exposed to x rays from a GE Senographe 2000D mammography unit at the surface and different depths within a BR12 phantom. X-ray beams were generated with Mo/Mo, Mo/Rh, and Rh/Rh anode/filter combinations and voltages between 25 and 34 kV. Glow curves were deconvoluted into component peaks and the high- to low-temperature ratio (HLTR) was evaluated. The photon field Eeff was obtained from the HLTR values using a calibration curve determined previously. PDD was established from the peak 5 TL signal (TLSP5 ) at depths between 0.0 and 3.5 cm inside the phantom. Taking into account the differences in density and composition between CaF2 :Tm and breast tissue, an energy-dependent correction factor (ß(E)) was applied to TLSP5 . Measurements were compared with radiation transport Monte Carlo (MC) simulations performed with PENELOPE-2008. RESULTS: A typical 5% change in the HLTR from the phantom top surface to 3.5 cm depth was measured, which corresponds to a 2.2 keV increase in photon field Eeff . Values of the ß(E) correction factor were 0.33 and 0.13 for Eeff equal to 15.1 and 22.5 keV, respectively. This strong energy dependence of ß(E) is mostly due to the differences in fluence attenuation between CaF2 and breast tissue. According to PDD measurements, dose decreased to half the surface value at depths between 0.7 and 1.0 cm for Mo/Mo/25 and Rh/Rh/34 beams, respectively. Values of PDD, less than 10% at 3.5 cm depth, would have been overestimated by about 3.5% (a large relative error) if an energy-independent correction factor had been assumed. Mean differences between experiments and MC simulations were 0.8 keV and 1.2% in the determination of Eeff and PDD, respectively. CONCLUSION: The TLD-300 glow curve was used to accurately measure the photon field Eeff and PDD within a mammographic phantom. This work has demonstrated that Eeff and dose can be established simultaneously by using solely TLD-300.

Telediagnosis of oral lesions in primary care: The EstomatoNet Program.

OBJECTIVE: The diagnosis of oral lesions is often challenging for primary healthcare providers, which explains the high number of referrals to specialist care. This favors increases in waiting lines and delays in diagnosis, contributing to high mortality rates from oral cancer. This study aimed to summarize the experience of the EstomatoNet, a telediagnosis program catering to primary care dentists and physicians from southern Brazil. STUDY DESIGN: This exploratory study included all queries received by EstomatoNet from June 2015 to December 2016. Health providers (71 dentists and 18 physicians from primary care) submitted requests including clinical information and photographs of oral lesions by means of a cloud-based platform. Specialized oral medicine teleconsultants received the data, conveyed a diagnostic hypothesis, and conveyed management recommendations. RESULTS: Actinic cheilitis (n = 41, 15.8%), squamous cell carcinoma (n = 22, 8.5%), and inflammatory hyperplasia (21, 8.1%) were the most frequent diagnoses. Teleconsultants recommended referral to specialists in 42.9% of the cases, total biopsy in 23.6%, and follow-up in 16.2%. After the EstomatoNet use, the intention to refer the patients to face-to-face consultation reduced from 96.9% to 35.1%. CONCLUSION: Telediagnosis for oral lesions is feasible and has potential to improve the quality of primary health care by bridging the gap between primary and specialized health care.

Monte Carlo calculations of the cellular S-values for α-particle-emitting radionuclides incorporated into the nuclei of cancer cells of the MDA-MB231, MCF7 and PC3 lines.

S-values (dose per unit of cumulated activity) for alpha particle-emitting radionuclides and monoenergetic alpha sources placed in the nuclei of three cancer cell models (MCF7, MDA-MB231 breast cancer cells and PC3 prostate cancer cells) were obtained by Monte Carlo simulation. The MCNPX code was used to calculate the fraction of energy deposited in the subcellular compartments due to the alpha sources in order to obtain the S-values. A comparison with internationally accepted S-values reported by the MIRD Cellular Committee for alpha sources in three sizes of spherical cells was also performed leading to an agreement within 4% when an alpha extended source uniformly distributed in the nucleus is simulated. This result allowed to apply the Monte Carlo Methodology to evaluate S-values for alpha particles in cancer cells. The calculation of S-values for nucleus, cytoplasm and membrane of cancer cells considering their particular geometry, distribution of the radionuclide source and chemical composition by means of Monte Carlo simulation provides a good approach for dosimetry assessment of alpha emitters inside cancer cells. Results from this work provide information and tools that may help researchers in the selection of appropriate radiopharmaceuticals in alpha-targeted cancer therapy and improve its dosimetry evaluation.

Measurements of radiation exposure of dentistry students during their radiological training using thermoluminescent dosimetry.

Exposure among dentistry students has not been assessed or regulated in Mexico. This work assessed the average exposure of 35 dentistry students during their training with the aid of LiF:Mg,Cu,P+PTFE thermoluminescent dosimeters. For the students in the roles of dentist and observers, maximum accumulated equivalent dose obtained was 2.59±0.11 and 4.64±0.39 mSv, respectively. Students in the role as patients received a maximum accumulated effective dose of 28.41±0.31 mSv. If compared to occupational dose limits, this latter value is 56% of the recommended value of 50 mSv in any year. It was found that in all cases, values of equivalent dose to the women breasts were equal to the background dose. Results are discussed and compared to previous published work. Suggested recommendations were given to authorities in order to minimize exposure of the students in the role as patients.

Evolution of the CaF2:Tm (TLD-300) glow curve as an indicator of beam quality for low-energy photon beams.

We study the high- to low- temperature signal ratio (HLTR) of the CaF2:Tm glow curve as a function of beam quality for low-energy photon beams with effective energy between 15.2 and 33.6 keV, generated with W, Mo and Rh anodes. CaF2:Tm dosemeters (TLD-300) were exposed to x-rays and (60)Co gamma-rays. Glow curves were deconvoluted into 7 peaks, using computerized glow curve deconvolution and HLTR was evaluated. Air kerma and dose in water were between 2.1-15.0 mGy and 49.8-373.8 mGy, respectively. All peaks in the glow curve showed a linear response with respect to air kerma and dose in water. HLTR values decreased monotonically between 1.029 ± 0.010 (at 15.2 keV) and 0.821 ± 0.011 (33.6 keV), and no effects due to the use of different anode/filter combinations were observed. The results indicate a relatively high value of HLTR (about 1 for 17 keV effective energy, or 3 keV µm(-1) track-average LET) and a measurable dependence on the photon beam quality. Comparison of these photon data with HLTR for ions shows good quantitative agreement. The reported evolution of the CaF2:Tm glow curve could facilitate the estimation of the effective energy of unknown photon fields by this technique.

Measurement of radiation exposure in relatives of thyroid cancer patients treated with (131)I.

This work evaluates the radiological risk that patients treated with I for differentiated thyroid cancer could present to relatives and occupationally exposed workers. Recently, the International Atomic Energy Agency issued document K9010241, which recommends that patient discharge from the hospital must be based on the particular status of each patient. This work measures effective dose received by caregivers of patients treated with I at the Instituto Nacional de Cancerología, Mexico City. Thermoluminescent dosimeters were carried during a 15-d period by 40 family caregivers after patient release from hospital. Relatives were classified into two groups, ambulatory and hospitalized, according to the release mode of the patient, and three categories according to the individual patient home and transport facilities. Categories A, B, and C were defined going from most to least adequate concerning public exposure risk. Measurements were performed for 20 family caregivers in each group. The effective dose received by all caregivers participating in this study was found to be less than 5 mSv, the recommended limit per event for caregivers suggested by ICRP 103. In addition, 70 and 90% of ambulatory and hospitalized groups, respectively, received doses lower than 1 mSv. Caregivers belonging to category C, with home situations that are not appropriate for immediate release, received the highest average doses; i.e., 2.2 ± 1.3 and 3.1 ± 1.0 mSv for hospitalized and ambulatory patients, respectively. Results of this work have shown that the proper implementation of radiation protection instructions for relatives and patients can reduce significantly the risk that differentiated thyroid cancer patients treated with I can represent for surrounding individuals. The results also stress the relevance of the patient's particular lifestyle and transport conditions as the prevailing factors related to the dose received by the caregiver. Therefore, the patient's status should be the criterion used to decide his/her release modality. This work provides support to recommend the implementation of the "patient specific release criteria" in accordance with ICRP 94, IAEA Safety Report No. 63, and IAE document K9010241 A for patients treated with radiopharmaceuticals.

Matching 4.7-Å XRD spacing in amelogenin nanoribbons and enamel matrix.

The recent discovery of conditions that induce nanoribbon structures of amelogenin protein in vitro raises questions about their role in enamel formation. Nanoribbons of recombinant human full-length amelogenin (rH174) are about 17 nm wide and self-align into parallel bundles; thus, they could act as templates for crystallization of nanofibrous apatite comprising dental enamel. Here we analyzed the secondary structures of nanoribbon amelogenin by x-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) and tested if the structural motif matches previous data on the organic matrix of enamel. XRD analysis showed that a peak corresponding to 4.7 Å is present in nanoribbons of amelogenin. In addition, FTIR analysis showed that amelogenin in the form of nanoribbons was comprised of ß-sheets by up to 75%, while amelogenin nanospheres had predominantly random-coil structure. The observation of a 4.7-Å XRD spacing confirms the presence of ß-sheets and illustrates structural parallels between the in vitro assemblies and structural motifs in developing enamel.

Dose per unit cumulated activity (S-values) for e⁻ and beta emitting radionuclides in cancer cell models calculated by Monte Carlo simulation.

Cell dosimetry is relevant regarding new efforts in specific molecular radiotherapy using Auger, CE and beta emitters. Absorbed dose in cells can be obtained by means of the dose per unit cumulated activity (S-values), together with the activity distribution. In this work, Monte Carlo simulation codes PENELOPE and MCNPX were used to obtain cellular S-values for point and extended sources of electrons and beta emitting radionuclides in the nucleus of breast (MDA-MB231, MCF7) and prostate (PC3) cancer cell models.

Response of LiF:Mg,Ti to low energy carbon and oxygen ions.

The extended track interaction model (ETIM) has been formulated to explain the TL-fluence response for peak 5 to heavy ions using radial dose distributions produced by the ions in LiF and their luminescent centre occupation probability distributions. In this work, an experimental study of the TLD-100 fluence response to carbon and oxygen ions and its interpretation in terms of a Monte Carlo simulation of ETIM applied to peak 5 are presented. Irradiations were performed with 7.34 and 10.3 MeV 12C and 8.34 MeV 16O ions in the fluence interval between 2 x 10(7) and 2 x 10(11) cm(-2). Individual glow curve responses show the expected increase of supralinearity as the peak temperature increases. Data for peak 5 show a weak dependence with energy. These latter results are difficult to understand when one considers the differences in the expected radial occupancies for different ion energies.

Track structure approach to the calculation of peak 5a to peak 5 (TLD-100) relative intensities following heavy charged particle irradiation.

A track structure approach to the calculation of the relative strength of localised and delocalised recombination mechanisms leading to composite glow peak 5 in LiF:Mg,Ti following heavy charged particle irradiation is described.