Morphobiological, morphometric and ultrastructural characterization of sylvatic Trypanosoma cruzi isolates from Rio de Janeiro state, Brazil / Caracterização morfobiológica, morfométrica e ultraestrutural de isolados silvestres de Trypanosoma cruzi do estado do Rio de Janeiro, Brasil

Abstract Triatoma vitticeps is a triatomine with geographic distribution restrict to Brazil, which exhibits high prevalence of Trypanosoma cruzi natural infection. Of special epidemiologic concern, this species often invades households in the states of Rio de Janeiro, Minas Gerais and Espírito Santo. The objective of this study was to evaluate morphological and ultrastructural parameters on three T. cruzi isolates obtained from wild T. vitticeps specimens. The growth and cell differentiation of the parasite was evaluated through epimastigote and trypomastigote forms obtained in the growth curves for three distinct isolates. The maximum growth showed differences at the 20th day of the curve. Our in vitro results show a heterogeneity, regarding these features for samples cultivated under the same conditions. Morphometric analyzes based on the shape of epimastigotes and trypomastigotes corroborated such differentiation. These results highlight the need of better understanding the meaning of this diversity under an eco-epidemiological perspective.

Resumo Triatoma vitticeps é um triatomíneo com distribuição geográfica restrita ao território brasileiro, apresentando alta prevalência de infecção natural pelo Trypanosoma cruzi. Esta espécie é relevante sob o ponto de vista epidemiológico por invadir domicílios com frequência nos estados do Rio de Janeiro, Minas Gerais e Espírito Santo. O objetivo deste estudo foi avaliar parâmetros morfológicos e ultraestruturais, em três isolados de T. cruzi obtidos a partir de triatomíneos silvestres. O crescimento e a diferenciação celular do parasita foi avaliado através das formas epimastigotas e tripomastigotas obtidas nas curvas de crescimento para os três isolados. O crescimento máximo mostrou diferenças no 20º dia da curva. Nossos resultados in vitro mostram uma heterogeneidade, em relação a essas características para amostras cultivadas nas mesmas condições. As análises morfométricas baseadas na conformação de epimastigotas e trypomastigotes corroboraram essa diferenciação. Estes resultados ressaltam a necessidade de uma melhor compreensão do significado desta diversidade sob uma perspectiva eco-epidemiológica.

Morphobiological, morphometric and ultrastructural characterization of sylvatic Trypanosoma cruzi isolates from Rio de Janeiro state, Brazil.

Triatoma vitticeps is a triatomine with geographic distribution restrict to Brazil, which exhibits high prevalence of Trypanosoma cruzi natural infection. Of special epidemiologic concern, this species often invades households in the states of Rio de Janeiro, Minas Gerais and Espírito Santo. The objective of this study was to evaluate morphological and ultrastructural parameters on three T. cruzi isolates obtained from wild T. vitticeps specimens. The growth and cell differentiation of the parasite was evaluated through epimastigote and trypomastigote forms obtained in the growth curves for three distinct isolates. The maximum growth showed differences at the 20th day of the curve. Our in vitro results show a heterogeneity, regarding these features for samples cultivated under the same conditions. Morphometric analyzes based on the shape of epimastigotes and trypomastigotes corroborated such differentiation. These results highlight the need of better understanding the meaning of this diversity under an eco-epidemiological perspective.

Colon cancer metastasis to the thyroid gland: A case report.

INTRODUCTION: Thyroid metastases from colorectal cancer are uncommon and few cases are described in literature. CASE PRESENTATION: A 64-year-old female patient presented with an asymptomatic right cervical nodule with a rapid growth six years after sigmoidectomy for cancer and two years after resection of colorectal lung metastases. Increased CA 19.9 was identified and a thoracoabdominal CT scan revealed the onset of new metastatic bilateral pulmonary lesions. Neck ultrasonography showed a suspicious nodule in the right thyroid lobe, and Fine-needle Aspiration Cytology (FNAC) of the nodule lead to the diagnosis of colorectal cancer metastasis. A right thyroid lobectomy with right central lymph node dissection was performed. The patient underwent chemotherapy with response, but this was posteriorly suspended due to haematological side effects, and the disease spread. DISCUSSION: Thyroid metastases from colorectal cancer are rare, but, with the improvement of radiologic exams and the higher survival rate of these patients, more cases are being described. The majority of the cases present pulmonary and hepatic metastases and the prognosis is poor. The decision to operate and the type of operation depend on the extent of the metastatic disease and the patient's overall condition. CONCLUSION: A low threshold of suspicion is crucial to make a timely diagnosis of thyroid metastases from colorectal cancer. Treatment is controversial, but, without surgery, the need may arise for tracheostomy.

Morphobiological, morphometric and ultrastructural characterization of sylvatic Trypanosoma cruzi isolates from Rio de Janeiro state, Brazil

Abstract Triatoma vitticeps is a triatomine with geographic distribution restrict to Brazil, which exhibits high prevalence of Trypanosoma cruzi natural infection. Of special epidemiologic concern, this species often invades households in the states of Rio de Janeiro, Minas Gerais and Espírito Santo. The objective of this study was to evaluate morphological and ultrastructural parameters on three T. cruzi isolates obtained from wild T. vitticeps specimens. The growth and cell differentiation of the parasite was evaluated through epimastigote and trypomastigote forms obtained in the growth curves for three distinct isolates. The maximum growth showed differences at the 20th day of the curve. Our in vitro results show a heterogeneity, regarding these features for samples cultivated under the same conditions. Morphometric analyzes based on the shape of epimastigotes and trypomastigotes corroborated such differentiation. These results highlight the need of better understanding the meaning of this diversity under an eco-epidemiological perspective.

Resumo Triatoma vitticeps é um triatomíneo com distribuição geográfica restrita ao território brasileiro, apresentando alta prevalência de infecção natural pelo Trypanosoma cruzi. Esta espécie é relevante sob o ponto de vista epidemiológico por invadir domicílios com frequência nos estados do Rio de Janeiro, Minas Gerais e Espírito Santo. O objetivo deste estudo foi avaliar parâmetros morfológicos e ultraestruturais, em três isolados de T. cruzi obtidos a partir de triatomíneos silvestres. O crescimento e a diferenciação celular do parasita foi avaliado através das formas epimastigotas e tripomastigotas obtidas nas curvas de crescimento para os três isolados. O crescimento máximo mostrou diferenças no 20º dia da curva. Nossos resultados in vitro mostram uma heterogeneidade, em relação a essas características para amostras cultivadas nas mesmas condições. As análises morfométricas baseadas na conformação de epimastigotas e trypomastigotes corroboraram essa diferenciação. Estes resultados ressaltam a necessidade de uma melhor compreensão do significado desta diversidade sob uma perspectiva eco-epidemiológica.

Collagen implant with gentamicin sulphate as an option to treat a neuroischaemic diabetic foot ulcer: Case report.

INTRODUCTION: The ischaemic diabetic foot is associated with a faster evolving atherosclerosis affecting preferentially the bellow knee arteries. This distal ischemia associated with a wide distribution of multiple stenosis and occlusions throughout lower limb arteries, makes revascularization very hard or even impossible. This represents a major factor responsible for non-healing diabetic foot ulcer. In these cases all efforts should be made to find treatment alternatives that can promote ulcer healing. CASE PRESENTATION: Male patient with neuroischaemic diabetic foot ulcer with exposure tendon, without possibility for endovascular or surgical revascularization, was treated unsuccessfully with prostaglandin and several types of dressings for 7 months. Skin graft failed. Weekly dressings with collagen implant impregnated with gentamicin sulphate were then started and continued in an outpatient setting. Evolution was very positive, with 99% of epithelisation in 9 months. No pain or infection since the beginning of this treatment. DISCUSSION: Successful treatment of a neuroischaemic diabetic foot ulcer rests with the possibility of increasing the perfusion to the foot. Whether or not a revascularization procedure is possible will set the tone for the ensuing treatment. Using collagen implant with gentamicin sulphate, collagen is delivered to the wound bed helping in the granulation tissue formation, will increase microcirculation, and topic gentamicin will decrease bacterial load, exudate and proteases production, increasing cicatrisation. CONCLUSION: In neuroischaemic diabetic foot ulcer weekly dressings with collagen implant impregnated with gentamicin sulphate can be a good option for ulcer healing.

[Irradiation of internal mammary nodes: State of the art]. / État de l'art de l'irradiation des ganglions de la chaîne mammaire interne.

In the adjuvant breast cancer treatment, postoperative radiotherapy plays a principal part with an action against the microscopic residual disease in the lymph nodes after mastectomy as well as after breast conserving surgery. This positive effect is observed also in the case of small inner lesions in patients without lymph node involvement. At the same time, there is a recognized risk of cardiac toxicity directly related to the irradiation of internal mammary nodes. This paper is a report on the current available techniques to irradiate the internal mammary nodes, including promising new technology that may help limiting the risk of cardiac toxicity.

Adult right-sided Bochdalek hernia with ileo-cecal appendix: Almeida-Reis hernia.

INTRODUCTION: Bochdalek hernia is one of the most common congenital abnormalities manifested in infants. In the adult is a rarity, with a prevalence of 0.17-6% of all diaphragmatic hernias. Right-sided Bochdalek hernias containing colon are even more rare, with no case described in the literature with ileo-cecal appendix. PRESENTATION OF CASE: The authors present a case of a right-sided Bochdalek hernia in an adult female of 49 years old, presented with severe respiratory failure. During laparotomy for hernia correction, were found in an intrathoracic position the cecum and ileo-cecal appendix, the right colon and the transverse colon. DISCUSSION: Although useful in patient evaluation, clinical history and physical examination are not helpful in making diagnosis because of their nonspecific character. CT scan is the most accurate exam for making diagnosis. Most of the times there is no hernial sac. Surgery is the treatment of choice, and it is always indicated even if asymptomatic. In general suture of the defect is possible. Due to patient's weak respiratory function we chose laparotomy by Kocher incision. CONCLUSION: Being the first case of a right-sided Bochdalek hernia in the adult with a herniated ileo-cecal appendix, we name it Almeida-Reis hernia.

Compatibility characteristics of five radiographic films utilised in Brazilian diagnostic radiology.

To evaluate the quality of the radiographic films in Brazil, according to the recommendations of ISO 9236-1, a radiographic images simulator was used. A study of the control of the quality in radiographic films was implemented. With regard to this study, the results of five films of different manufacturers are presented. The characteristic curves for the ISO qualities of 55, 70, 90 and 120 kV are presented. The PTW REX simulator was used to determine the image quality parameters. Film 2 presents problems due to high sensitivity. Film 1 has a higher energy dependence than the other films. Film 5 yields the best results for almost all the sensitometric parameters. In conclusion, existing films in the Brazilian market vary considerably with relation to image quality.

Visualisation of the left anterior descending coronary artery on CT images used for breast radiotherapy planning.

OBJECTIVE: To assess the visualisation of the left anterior descending (LAD) coronary artery on CT images used for breast radiation treatment planning. METHODS: Delineation of the LAD artery was achieved for 25 breast patients by 1 radiologist and 1 radiation oncologist independently on two sets of images for each patient: one pre-operative CT scan using intravenous (IV) contrast media to determine the primary gross tumour volume (GTV) and one post-operative CT scan used for treatment planning. A Student's paired t-test was used to compare the number of CT slices in which the LAD was visible for each patient in the two series. Interpolations and extrapolations of the LAD volume were performed for the left-sided cases using a published heart atlas in order to report doses to the LAD structure. RESULTS: There was a non-significant difference between the results with and without IV contrast media (p=0.34 for the radiologist; p=0.90 for the radiation oncologist). The visible LAD artery corresponded to a 30% portion (range 12-47%) of the interpolated structure. The maximum dose to the left artery varied widely, from 2.7 to 41.7 Gy, in the group of patients with left breast tumours. The largest values (>25 Gy) corresponded to those patients in whom the LAD artery distal extremity lay inside the breast fields. CONCLUSIONS: With the current planning CT protocol, only one-third of the LAD artery could be objectively visualised. Contrast-enhanced imaging used for GTV delineation before the breast surgery did not improve the visualisation of the artery. ADVANCES IN KNOWLEDGE: This study has revealed the lack of consistency that may be encountered when contouring heart vessels, thereby questioning the reliability of dose reporting.

Potential benefits of using cardiac gated images to reduce the dose to the left anterior descending coronary during radiotherapy of left breast and internal mammary nodes.

PURPOSE: To assess the benefits of using cardiac gated images for treatment planning of breast and internal mammary nodes. PATIENTS AND METHODS: Inspiration breath hold computed tomography (CT) series acquired at prospectively gated diastolic phase were used for planning. Three different techniques were compared. Technique A used tangents and an internal mammary nodes field covering the three first inter-rib spaces; technique B used an extended internal mammary nodes including part of the medial breast in junction with tangential fields; the 3(rd) technique used helical tomotherapy. For each technique, two treatment plans were performed: one plan (plan-01) where mean dose and V(25) to the heart were considered for plan evaluation and a second plan (plan-02) where the irradiation of the left anterior descending artery was minimized. RESULTS: V(25) to the heart was found to be less than 5% for all six plans. Mean doses to the heart were within 4.8 to 7.2 Gy. By attempting to lower the dose to the left anterior descending artery, heart D(mean) was decreased by 20-30% for the two techniques A and B while being unchanged for tomotherapy. Regarding target coverage, there was no marked difference between plans where only heart dose was considered (plans-01) and plans where the left anterior descending artery dose was minimized (plans-02). When the left anterior descending artery dose was part of plan evaluation, D(mean) to the left anterior descending artery could be decreased by 24, 19 and 9% for techniques A, B and tomotherapy respectively. The three techniques exposed segments of the left coronary to different levels of dose. CONCLUSION: This study showed that evaluation of the dose to the left anterior descending artery coronary may change the treatment strategy. Cardiac gated images without IV contrast permitted a good visualization of the coronaries in order to optimize the dose on these structures. In addition to heart V(25,) the dose to the coronaries should be included in prospective studies on radiotherapy related heart toxicity in association with all additional risk factors.

Could the bug Triatoma sherlocki be vectoring Chagas disease in small mining communities in Bahia, Brazil?

Searches for Chagas disease vectors were performed at the type locality from which Triatoma sherlocki Papa et al. (Hemiptera: Reduviidae: Triatominae) was described in the municipality of Gentio do Ouro, in the state of Bahia, Brazil, and in a small artisan quarry-mining community approximately 13 km distant in a remote area of the same municipality. The latter site represents a new locality record for this species. Adults, nymphs and exuviae of T. sherlocki were found in 21% of human dwellings, indicating that the species is in the process of domiciliation. Prevalence of Trypanosoma cruzi infection in collected bugs was 10.8%. Simple predictive approaches based on environmental similarity were used to identify additional sites likely suitable for this species. The approach successfully predicted an additional five sites for the species in surrounding landscapes. Ecological and entomological indicators were combined to discuss whether this scenario likely represents an isolated case or an emerging public health problem.

Hydrogen peroxide induces a specific DNA base change profile in the presence of the iron chelator 2, 2’ dipyridyl in Escherichia coli

Pretreatment of Escherichia coli cultures with the iron chelator 2,2’-dipyridyl (1 mM) protects against the lethal effects of low concentrations of hydrogen peroxide (<15 mM). However, at H2O2 concentrations equal to or greater than 15 mM, dipyridyl pretreatment increases lethality and mutagenesis, which is attributed to the formation of different types of DNA lesions. We show here that pretreatment with dipyridyl (1 mM) prior to challenge with high H2O2 concentrations (≥15 mM) induced mainly G:C→A:T transitions (more than 100X with 15 mM and more than 250X with 20 mM over the spontaneous mutagenesis rate) in E. coli. In contrast, high H2O2 concentrations in the absence of dipyridyl preferentially induced A:T→T:A transversions (more than 1800X and more than 300X over spontaneous mutagenesis for 15 and 20 mM, respectively). We also show that in the fpg nth double mutant, the rpoB gene mutation (RifS-RifR) induced by 20 mM H2O2 alone (20X higher) was increased in 20 mM H2O2 and dipyridyl-treated cultures (110X higher), suggesting additional and/or different lesions in cells treated with H2O2 under iron deprivation. It is suggested that, upon iron deprivation, cytosine may be the main damaged base and the origin of the pre-mutagenic lesions induced by H2O2.

Hydrogen peroxide induces a specific DNA base change profile in the presence of the iron chelator 2,2' dipyridyl in Escherichia coli.

Pretreatment of Escherichia coli cultures with the iron chelator 2,2'-dipyridyl (1 mM) protects against the lethal effects of low concentrations of hydrogen peroxide (<15 mM). However, at H(2)O(2) concentrations equal to or greater than 15 mM, dipyridyl pretreatment increases lethality and mutagenesis, which is attributed to the formation of different types of DNA lesions. We show here that pretreatment with dipyridyl (1 mM) prior to challenge with high H(2)O(2) concentrations (>or=15 mM) induced mainly G:C-->A:T transitions (more than 100X with 15 mM and more than 250X with 20 mM over the spontaneous mutagenesis rate) in E. coli. In contrast, high H(2)O(2) concentrations in the absence of dipyridyl preferentially induced A:T-->T:A transversions (more than 1800X and more than 300X over spontaneous mutagenesis for 15 and 20 mM, respectively). We also show that in the fpg nth double mutant, the rpoB gene mutation (RifS-RifR) induced by 20 mM H(2)O(2) alone (20X higher) was increased in 20 mM H(2)O(2) and dipyridyl-treated cultures (110X higher), suggesting additional and/or different lesions in cells treated with H(2)O(2) under iron deprivation. It is suggested that, upon iron deprivation, cytosine may be the main damaged base and the origin of the pre-mutagenic lesions induced by H(2)O(2).

Genetic variability of Triatoma rubrovaria (Reduviidae: Triatominae) from Brazil, Argentina and Uruguay as revealed by two different molecular markers.

Randomly amplified polymorphic DNA (RAPD) and nuclear ribosomal DNA sequence analyses were used to assess the genetic population structure of the South American triatomine species Triatomo rubrovario throughout its geographical distribution. To investigate the genetic variability at both intraspecific and intrapopulational levels the RAPD profiles and the nucleotide sequences of the rDNA intergenic spacers, ITS-1 and ITS-2, were analysed and compared. The phenetic analysis based on RAPD profiles show three distinct clusters diverging by similarity coefficients ranging from 0.62 to 0.96. The ITS-1 and ITS-2 sequence variability detected may be considered very high, suggesting reproductive isolation between populations. A total of seven composite haplotypes (CH) were found, among which three are specific for Brazil, other three for Uruguay, and the last one common for the three countries studied. The population studied in Argentina does not represent an independent CH. Sequence analyses proved that the five populations studied are easily differentiable and that there is heterogeneity within each one. True mutations and indels are the responsible of sequence differences between haplotypes and populations, suggesting that divergence processes may presently go on within this species. The large intraspecific variability detected may underlie the known plasticity of T. rubrovaria, making it a potential intradomiciliary invader and consequently an appropriate vector for Chagas disease transmission. Therefore, this triatomine species must be continuously monitored throughout.

Quality assurance of HDR 192Ir sources using a Fricke dosimeter.

A prototype of a Fricke dosimetry system consisting of a 15 x 15 x 15 cm3 water phantom made of Plexiglas and a 11.3-ml Pyrex balloon fitted with a 0.2 cm thick Pyrex sleeve in its center was created to assess source strength and treatment planning algorithms for use in high dose rate (HDR) 192Ir afterloading units. In routine operation, the radioactive source is positioned at the end of a sleeve, which coincides with the center of the spherical balloon that is filled with Fricke solution, so that the solution is nearly isotropically irradiated. The Fricke system was calibrated in terms of source strength against a reference well-type ionization chamber, and in terms of radial dose by means of an existing algorithm from the HDR's treatment planning system. Because the system is based on the Fricke dosimeter itself, for a given type and model of 192Ir source, the system needs initial calibration but no recalibration. The results from measurements made over a 10 month period, including source decay and source substitutions, have shown the feasibility of using such a system for quality control (QC) of HDR afterloading equipment, including both the source activity and treatment planning parameters. The benefit of a large scale production and the use of this device for clinical HDR QC audits via mail are also discussed.

RAPD analyses and rDNA intergenic-spacer sequences discriminate Brazilian populations of Triatoma rubrovaria (Reduviidae: Triatominae).

Triatoma rubrovaria, a member of the 'infestans' subgroup, is a potential vector of Trypanosoma cruzi in southern Brazil. Surveillance data indicate a growing domiciliary and peridomiciliary invasion by Tri. rubrovaria in the rural areas of Rio Grande do Sul (RS). In fact, following effective control of Tri. infestans, Tri. rubrovaria, which seems to have pre-adaptative characteristics for anthropic ecotopes, has become the most frequent species of triatomine bug to be collected in these areas. To explore the intraspecific variability and domiciliation of Tri. rubrovaria, the ribosomal DNA (rDNA) of two RS populations of Tri. rubrovaria that were geographically separated by only 220 km was investigated. The RAPD profiles and nucleotide sequences of the intergenic region of the rDNA, including the internal transcribed spacers 1 and 2 (ITS-1 and ITS-2) and the 5.8S gene, were analysed. In the RAPD study, the use of three decameric primers revealed polymorphisms reflecting both genetic differences between the two populations and heterogeneity within each. A phenetic dendrogram of the Tri. rubrovaria specimens, based on the three-primer consensus and a simple-matching coefficient of similarity, showed two clusters, clearly differentiating the bugs from the two localities studied. The rDNA sequencing revealed four different nucleotide sequences, with two different genotypes in each locality. The level of intraspecific variability detected within ITS-1 and ITS-2 of the Tri. rubrovaria, which was remarkably high considering the physical closeness of the two populations sampled, may indicate that the two collection sites are separated by geographical barriers that ensure the reproductive isolation of each population. The ITS sequences, like the RAPD results, clearly distinguished the two populations while showing that there is heterogeneity within each of them. The present study appears to be the first to reveal ITS length differences between populations of the same triatomine species without any associated difference in the number of microsatellite repeats. These results are in agreement with those of earlier studies on iso-enzymes, chromatic patterns, the ecological effects of environmental modification by humans, and bloodmeal sources.

Oral subchronic toxicity of aqueous crude extract of Plantago australis leaves.

The toxic effects of chronic oral administration (60 days) of aqueous crude extract (AE) of Plantago australis Lam. (Plantaginaceae) in rats at doses of 850 and 1700 mg/kg on biochemical (ALT, AST, creatinine, urea, glucose, alkaline phosphatase, total proteins and albumin), hematological (complete hemogram), and histopathological (heart, lung, liver, kidney, esophagus, stomach and gut) parameters were studied. All biochemical and hematological parameters were found to be in the normal range, but ALT in animals that received AE of 850 mg/kg was higher. Histopathological analysis of organs, especially the liver did not present alterations.

Natural history of Ctenus medius Keyserling, 1891 (Aranae, Ctenidae) II: life cycle and aspects of reproductive behavior under laboratory conditions

Ctenus medius Keyserling, 1891 is a wandering spider common in the Brazilian Atlantic Forest. It has been the subject of few studies. Thus, this work aims to elucidate aspects of its natural history, such as the life cycle and reproductive behavior of this species, through laboratory and field observations. Two females with egg sacs were observed in the laboratory and one was observed in field (Barra Mansa, 22º32'S and 44º10'W) until the emergence of the spiderlings. For observation of the immature stage development, a portion of the spiderlings from the same hatch were taken to the laboratory and watched until sexual maturity. In the field, the period between the oviposition and the emergence of spiderlings was of 36 days. The female selects a site for egg sac deposition and stays there until the spiderlings emerge. Seven days after the emergence, the female abandoned the site where the egg sac was made, concomitant to the spiderlings dispersion from observation's place and until the moment that the spiderlings started to eat. For the spiderlings kept under laboratory conditions, cannibalism was not observed in the first instars (1-4th) when sufficient food was offered. Sexual maturity happened in the 14th or 15th instars, with an average of 309.2 to 344.5 days until the last/sexual molt, respectively. Until the date of sexual maturity, there was a mortality rate of 85 percent. This species is very fragile in captivity. This hampered deductions concerning longevity. Both females and males collected in the field were induced to mate in the laboratory. Courtship movements of males were registered, but the females did not permit the mating. These data may assist in initial biological studies of Ctenus genus and offer comparative parameters for studies of other related species

The influence of urbanization on natural radiation levels in anomalous areas.

This paper verifies the effects of urbanization on the original levels of environmental gamma radiation in an anomalous area. The fieldwork was done in the city of Guarapari, on the seacoast of the state of Espírito Santo, Brazil. This place was chosen because the whole region is naturally rich in monazite sand, which contains thorium and uranium. A similar study was also carried out in the 1960s. The measurements were done using an inorganic NaI scintillometer detector with Cu+Pb filters coupled to a scaler. The methodology of measurements used was similar to the one applied in the fieldwork carried out in the 1960s. In addition, a simulation was performed in the laboratory, to determine the attenuation of the materials used in the urbanization of the region. The results of this work clearly show that there was a reduction in the levels of external radiation in the streets and squares of Guarapari. It was concluded that the reduction was due to attenuation by the materials used in the urbanization.

Experimental derivation of wall correction factors for ionization chambers used in high dose rate 192Ir source calibration.

At present there are no specific primary standards for 192Ir high dose rate sources used in brachytherapy. Traceability to primary standards is guaranteed through the method recommended by the AAPM that derives the air kerma calibration factor for the 192Ir gamma rays as the average of the air kerma calibration factors for x-rays and 137Cs gamma-rays or the Maréchal et al. method that uses the energy-weighted air kerma calibration factors for 250 kV x rays and 60Co gamma rays as the air kerma calibration factor for the 192Ir gamma rays. In order to use these methods, it is necessary to use the same buildup cap for all energies and the appropriate wall correction factor for each chamber. This work describes experimental work used to derive the A(W) for four different ionization chambers and different buildup cap materials for the three energies involved in the Maréchal et al. method. The A(W) for the two most common ionization chambers used in hospitals, the Farmer NE 2571 and PTW N30001 is 0.995 and 0.997, respectively, for 250 kV x rays, 0.982 and 0.985 for 192Ir gamma rays, and 0.979 and 0.991 for 60Co gamma rays, all for a PMMA build-up cap of 0.550 gm cm(-2). A comparison between the experimental values and Monte Carlo calculations shows an agreement better than 0.9%. Availability of the A(W) correction factors for all commercial chambers allows users of the in-air calibration jig, provided by the manufacturer, to alternatively use the Maréchal et al. method. Calibration laboratories may also used this method for calibration of a well-type ionization chamber with a comparable accuracy to the AAPM method.