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At least 937 records · Page 52Linked to original sources
PubMed1998

The indirect use of CT numbers to establish material properties needed for Monte Carlo calculation of dose distributions in patients.

A number of Monte Carlo codes are available, which can be used to calculate dose distributions n patients with high accuracy. Patient geometry can readily be derived with adequate spatial resolution from CT scans. To perform the Monte Carlo calculation with the same spatial resolution, it is necessary to enter the atomic composition and density of the tissue in each voxel of the CT image. This means entering 65,536 discrete values for a CT slice with a 256 x 256 matrix size. The need for automated methods of setting up the material data files is obvious. Because there is no direct unique relationship between CT numbers and material composition, the aim of our work was to devise a method whereby the atomic composition and density in each voxel could be assigned automatically by indirect derivation from the CT numbers. The set of all tissues types in the human body was divided into subsets that are dosimetrically equivalent, based on Monte Carlo calculated depth dose curves in homogeneous phantoms of each tissue. CT number ranges corresponding to each tissue subset were determined from the calibration curve linking electron density with CT number for the specific CT scanner. Further subdivision was found to be necessary for the lung and bone type tissues. This was done by keeping the atomic composition constant and varying the physical density. It was found that 57 distinct tissue subsets were needed to represent the 16 main tissue types in the body at a 1% dose level. Corresponding CT number intervals of 30 HU were needed in the lung and soft tissue region, whereas in the bone region the intervals could be increased to 100 HU. A computer algorithm was set up to convert automatically from CT number to corresponding equivalent material number for the Monte Carlo preprocessor code.

Algorithms↗
PubMed1999

Correlated histogram representation of Monte Carlo derived medical accelerator photon-output phase space.

We present a method for condensing the photon energy and angular distributions obtained from Monte Carlo simulations of medical accelerators. This method represents the output as a series of correlated histograms and as such is well-suited for inclusion as the photon-source package for Monte Carlo codes used to determine the dose distributions in photon teletherapy. The method accounts for the isocenter-plane variations of the photon energy spectral distributions with increasing distance from the beam central axis for radiation produced in the bremsstrahlung target as well as for radiation scattered by the various treatment machine components within the accelerator head. Comparison of the isocenter energy fluence computed by this algorithm with that of the underlying full-physics Monte Carlo photon phase space indicates that energy fluence errors are less than 1% of the maximum energy fluence for a range of open-field sizes. Comparison of jaw-edge penumbrae shows that the angular distributions of the photons are accurately reproduced. The Monte Carlo sampling efficiency (the fraction of generated photons which clear the collimator jaws) of the algorithm is approximately 83% for an open 10x10 field, rising to approximately 96% for an open 40x40 field. Data file sizes for a typical medical accelerator, at a given energy, are approximately 150 kB, compared to the 1 GB size of the underlying full-physics phase space file.

Computer Simulation↗
PubMed2003

An integrated treatment delivery system for CSRS and CSRT and clinical applications.

An integrated treatment delivery system for conformal stereotactic radiosurgery (CSRS) and radiotherapy (CSRT) has been developed through a collaboration involving Siemens Medical Systems, Inc., Tyco/Radionics, Inc., and The University of Texas M. D. Anderson Cancer Center. The system consists of a 6-MV linear accelerator (LINAC) equipped with a Tyco/Radionics miniature multileaf collimator (mMLC). For the conventional SRS treatment, the circular collimator housing can be attached to the opening window of the mMLC. The treatment delivery system is integrated with a radiotherapy treatment planning system and a record-and-verify system. The purpose of this study is to report the characteristics, performance, benefits, and the clinical applications of this delivery system. The technical specifications of the LINAC and mMLC were tested, and all the specifications were met. The 80% to 20% penumbral width for each mMLC leaf is approximately 3 mm and is nearly independent of the off-axis positions of a leaf. The maximum interleaf leakage is 1.4% (1.1% on average) and the maximum intra-leaf leakage is 1.0% (0.9% on average). The leaf position precision is better than 0.5 mm for all the leaves. The integration of the SRS/SRT treatment planning system, mMLC, and LINAC has been evaluated successfully for transferring the patient treatment data file through radiotherapy treatment planning system to the patient information and treatment record-and-verify server and the mMLC controller. Subsequently, the auto-sequential treatment delivery for SRS, CSRS/CSRT, and the step-and-shoot intensity-modulated radiotherapy has also been tested successfully. The accuracy of dose delivery was evaluated for a 2-cm spherical target in a Radiological Physics Center SRS head phantom with GAFChromic films and TLD. Five non-coplanar arcs, using a 2-cm diameter circular collimator, were used for this simulation treatment. The accuracy to aim the center of the spherical target was within 0.5 mm and the deviation of dose delivery to the isocenter of the target was within 2% of the calculated dose. For the irregularly shaped tumor, a tissue-equivalent head phantom was used to evaluate the accuracy of dose delivery for using either geometric conformal treatment or IMRT. The accuracy of dose delivery to the isocenter was within 2% and 3% of the calculated dose, respectively. From October 26, 1999 to September 30, 2002, we treated over 400 SRS patients and 70 SRT patients. Four representative cases are presented to illustrate the capabilities of this dedicated unit in performing conventional SRS, CSRS, and CSRT. For all the cases, the geometric conformal-plan dose distributions showed a high degree of conformity to the target shape. The degree of conformity can be evaluated using the target-volume-ratio (TVR). Our preferred TVR values for highly conformed dose distributions range from 1.6 to 2.0. The patient setup reproducibility for the Gill-Thomas-Cosman (GTC) noninvasive head frame ranges from 0.5 to 1 mm, and the head and neck noninvasive frame is within 2 mm. The integrated treatment delivery system offers excellent conformation for complicated planning target volumes with the stereotactic setup approach, ensuring that dose delivery can be achieved within the specified accuracy. In addition, the treatment time is comparable with that of single isocenter multiple-arc treatments.

Brain Neoplasms↗
PubMed2000

A software model to estimate zones of impact on marine mammals around anthropogenic noise.

Anthropogenic noise impacts marine mammals in a variety of ways. In order to estimate over which ranges this happens, we first need to understand the propagation of noise through the ocean away from the noise source, and, second, understand the relationship between received noise levels and impact thresholds. A software package combining both aspects is presented. (1) A sound propagation model based on ray theory was developed to calculate received noise levels as a function of range, depth, and frequency. (2) Current knowledge of noise impact thresholds for marine mammals was gathered and included in software routines predicting zones of impact on marine mammals around industrial underwater noise sources. As input parameters, this software package requires the source level and spectrum of the noise of interest; physical oceanography data about the local ocean environment such as bathymetry, bottom and surface loss data, and sound speed profiles; and bioacoustical information about the target species in the form of an audiogram, critical auditory bandwidths, spectra of typical animal vocalizations, reported sound levels of disturbance, and criteria for hearing damage. As output, the software produces data files and plots of the zones of audibility, masking, disturbance, and potential hearing damage around a noise source.

Animals↗
PubMed1994

In vivo liver differentiation by ultrasound using an artificial neural network.

A pattern recognition algorithm and instrumentation for in vivo ultrasound human liver differentiation are presented. An available 16-MHz microprocessor-based data acquisition and analysis system with 6-bit resolution is used to capture, digitize, and store the backscattered ultrasound signal. The algorithm is based on a multilayer perception neural network using the backpropagation training procedure. The network is implemented to differentiate between normal and abnormal liver. Data earlier obtained from 18 volunteers with normal liver history and from 12 volunteers with liver abnormalities are used to test the algorithm. The power spectra of the backscattered signal from depths of 5, 6.5, and 8 cm in the liver are calculated. The acoustic attenuation coefficient is calculated by the log spectral difference technique over the frequency range from 1.5 to 4.5 MHz. The change of speed of sound with frequency (dispersion) is estimated over the 3-MHz bandwidth. The attenuation and velocity dispersion are used as differentiation features. The results show that of the 22 tested cases, the system differentiated correctly 19 and 20 cases when using the attenuation and the velocity dispersion, respectively. The average magnitude of dispersion of liver is estimated to be 1.67 +/- 0.1 m/s/MHz and about 2.3 +/- 0.18 m/s/MHz in the normal and abnormal cases, respectively. The overall performance of the system for liver differentiation is 91% for normal cases, and 86% for abnormal cases. The data files are also differentiated using the nearest neighbor statistical classifier. The results show that of the 30 tested cases, 23 files are differentiated correctly using the attenuation coefficient.

Humans↗
PubMed2002

Identity and search in social networks.

Social networks have the surprising property of being "searchable": Ordinary people are capable of directing messages through their network of acquaintances to reach a specific but distant target person in only a few steps. We present a model that offers an explanation of social network searchability in terms of recognizable personal identities: sets of characteristics measured along a number of social dimensions. Our model defines a class of searchable networks and a method for searching them that may be applicable to many network search problems, including the location of data files in peer-to-peer networks, pages on the World Wide Web, and information in distributed databases.

Algorithms↗
PubMed1994

Hospital admissions before the age of 2 years in Western Australia.

A linked data file of birth records and hospital admissions was used to investigate inpatient hospital morbidity before 2 years of age for all non-Aboriginal and Aboriginal children born in Western Australia in 1986. Of the non-Aboriginal children, 31.8% were admitted to hospital at least once before the age of 2 years, with an overall admission rate of 526/1000 live births; the corresponding figures for Aboriginal children were 68.7% and 2797. The mean number of days in hospital for each non-Aboriginal child admitted was 7.4, and 26.5 for Aboriginal children. Of the total cohort, 21% of non-Aboriginal and 20% of Aboriginal children were admitted only once, and 4% of non-Aboriginal and 36% of Aboriginal children were admitted at least three times; 23% of non-Aboriginal and 24% of Aboriginal children were admitted for only one major disease category, and 1% of non-Aboriginal and 16% of Aboriginal children were in at least four categories. The highest admission rates and highest percentages of the cohort admitted were for gastrointestinal and respiratory diseases and social admissions. These results illustrate the importance for both descriptive and analytical research of relating admissions to hospital for the total population to the individual child, and of using clinically relevant disease classifications.

Cohort Studies↗
PubMed2006

Is there an association between pre-existing sleep apnoea and the development of glaucoma?

AIM: To determine if sleep apnoea is associated with an increased risk of developing glaucoma. METHODS: This was a nested case-control study. Patients seen at the Veterans Affairs Medical Center (BVAMC) in Birmingham, Alabama, with newly diagnosed glaucoma (cases) between 1997 through 2001 were selected (n = 667) and age matched with non-glaucomatous controls (n = 6667). Patient information was extracted from the BVAMC data files containing demographic, clinical, and medication information. An index date was assigned to the glaucoma subjects corresponding to the time of diagnosis. Patients who had a glaucoma diagnosis before the observation period of the study were excluded. 10 controls were randomly selected for each case and matched on age (plus or minus 1 year) and an encounter on or before the index date of the matched case. Ihe main outcome measures were crude and adjusted relative risks for the association between the previous diagnosis of sleep apnoea and the development glaucoma. Adjustment was performed for the associations of diabetes, lipid metabolism disorders, hypertension, cardiovascular disease, cerebrovascular disease, arterial disease, and migraines. RESULTS: Individuals who developed glaucoma were more likely to have a previous sleep apnoea diagnosis relative to control subjects. However, this finding was of borderline significance at an alpha of 0.05 (p value = 0.06, odds ratio = 2.20, 95% confidence intervals 0.967 to 5.004). Following adjustment for other potential risk factors, no significant difference was seen (p value = 0.18, odds ratio = 1.80, 95% confidence interval 0.76 to 4.23). CONCLUSIONS: This nested case-control study does not support a large impact of sleep apnoea on the eventual development of glaucoma relative to other putative risk factors.

Aged↗
PubMed1995

Provision of sex education and early sexual experience: the relation examined.

OBJECTIVES: To explore the relation between receipt of sex education and experience of first intercourse. SUBJECTS AND DESIGN: The national survey of sexual attitudes and lifestyles is based on a sample of 18,876 respondents aged 16-59, randomly selected from the Post Office's small-user postcode address file. Data were collected between May 1990 and November 1991 by personal interviews combining a self administered questionnaire with a face to face interview. MAIN OUTCOME MEASURES: Age at first intercourse, use of contraception at first intercourse, actual and preferred source of sex education (including school based lessons). RESULTS: Median age at first intercourse fell by four years for women and three years for men over the past four decades, to 17 for both men and women aged 16-19 at the time of interview. Of those respondents for whom school was the main source of information about sexual matters, men were less likely, and women no more likely, to have had intercourse before the age of 16 than were those citing other main sources, such as friends and the media. Both men and women were more likely to have used some method of contraception. In multivariate analysis, these effects remained after controlling for the effect of current age, educational attainment, and religious affiliation. CONCLUSIONS: These data provide no evidence to support the concern that provision of school sex education might hasten the onset of sexual experience. These findings have important implications for the provision of sexual health education and highlight the need to carry out prospective and randomised studies of the impact of sex education.

Adolescent↗
PubMed2003

Pharmaceutical industry sponsorship and research outcome and quality: systematic review.

OBJECTIVE: To investigate whether funding of drug studies by the pharmaceutical industry is associated with outcomes that are favourable to the funder and whether the methods of trials funded by pharmaceutical companies differ from the methods in trials with other sources of support. METHODS: Medline (January 1966 to December 2002) and Embase (January 1980 to December 2002) searches were supplemented with material identified in the references and in the authors' personal files. Data were independently abstracted by three of the authors and disagreements were resolved by consensus. RESULTS: 30 studies were included. Research funded by drug companies was less likely to be published than research funded by other sources. Studies sponsored by pharmaceutical companies were more likely to have outcomes favouring the sponsor than were studies with other sponsors (odds ratio 4.05; 95% confidence interval 2.98 to 5.51; 18 comparisons). None of the 13 studies that analysed methods reported that studies funded by industry was of poorer quality. CONCLUSION: Systematic bias favours products which are made by the company funding the research. Explanations include the selection of an inappropriate comparator to the product being investigated and publication bias.

Clinical Trials as Topic↗
PubMed1996

Airgun injuries in New Zealand, 1979-92.

OBJECTIVES: To describe the epidemiology of serious airgun injury in New Zealand. METHODS: Cases were selected from the New Zealand Health Information Service's hospital inpatient morbidity data files for the period 1979 to 1992 inclusive. RESULTS: There were 718 airgun related injuries resulting in 1.56 injuries/100,000 population/year. Males and 10-14 year olds had higher than average rates of injury. The majority of the incidents were unintentional. There has been a marked decline in injury rates since 1989. CONCLUSIONS: Airgun injuries, while not as serious as powder firearm injuries, account for a significant personal and societal burden. The results suggest that strategies aimed at controlling these injuries, especially those pertaining to children, are in need of review.

Accident Prevention↗
PubMed2005

Incidence of sports and recreation related injuries resulting in hospitalization in Wisconsin in 2000.

OBJECTIVE: To describe the incidence and patterns of sports and recreation related injuries resulting in inpatient hospitalization in Wisconsin. Although much sports and recreation related injury research has focused on the emergency department setting, little is known about the scope or characteristics of more severe sports injuries resulting in hospitalization. SETTING: The Wisconsin Bureau of Health Information (BHI) maintains hospital inpatient discharge data through a statewide mandatory reporting system. The database contains demographic and health information on all patients hospitalized in acute care non-federal hospitals in Wisconsin. METHODS: The authors developed a classification scheme based on the International Classification of Diseases External cause of injury code (E code) to identify hospitalizations for sports and recreation related injuries from the BHI data files (2000). Due to the uncertainty within E codes in specifying sports and recreation related injuries, the authors used Bayesian analysis to model the incidence of these types of injuries. RESULTS: There were 1714 (95% credible interval 1499 to 2022) sports and recreation-related injury hospitalizations in Wisconsin in 2000 (32.0 per 100,000 population). The most common mechanisms of injury were being struck by/against an object in sports (6.4 per 100,000 population) and pedal cycle riding (6.2 per 100,000). Ten to 19 year olds had the highest rate of sports and recreation related injury hospitalization (65.3 per 100,000 population), and males overall had a rate four times higher than females. CONCLUSIONS: Over 1700 sports and recreation related injuries occurred in Wisconsin in 2000 that were treated during an inpatient hospitalization. Sports and recreation activities result in a substantial number of serious, as well as minor injuries. Prevention efforts aimed at reducing injuries while continuing to promote participation in physical activity for all ages are critical.

Adolescent↗
PubMed2002

Adolescent injury morbidity in New Zealand, 1987-96.

OBJECTIVES: Adolescents are over-represented in injury statistics. New Zealand is privileged in having a hospital discharge database allowing for analysis of non-fatal injury data at a national level. An epidemiological description of adolescent injury morbidity is provided and options for prevention are discussed. METHOD: People aged 15-19 years admitted to hospital for their injuries in the period 1 987-96 were identified from the New Zealand Health Information Service morbidity data files. The manner, causes, and nature of injury were examined. Injury prevention strategies were reviewed. RESULTS: The incidence of hospitalised injury was 1,886 per 100,000 person years. The victims were male (70%). The leading causes of injury were road traffic crashes, sports injuries, and self poisoning. The most common injury diagnoses were head injuries (29%) and limb fractures (21%). Road traffic crashes produced the highest proportion of serious injuries. CONCLUSIONS: Road traffic crashes, sports injuries, and self inflicted poisoning, stood out as areas with the greatest potential for reducing the burden of injury in late adolescence. Graduated driver licensing shows promise as an injury prevention measure but remains inadequately implemented. Policies to reduce self inflicted poisoning are of unknown efficacy, and evidence is awaited on the effectiveness of measures to reduce injury in sport.

Adolescent↗
PubMed2002

Rising incidence of breast cancer after completion of the first prevalent round of the breast cancer screening programme.

OBJECTIVES: After completion of the prevalent screening round of the breast cancer screening programme in Limburg, The Netherlands, incidences started rising once again. This increase was contrary to expectations, which had predicted a slightly higher, but stable, incidence after the first screening round. The trends in incidence were studied to find explanations for the observed rise in incidence. SETTING: Breast cancer screening programme in mid-Limburg and southern Limburg, the Netherlands. METHODS: The data files of the breast cancer screening programme and the Maastricht cancer registry were linked to evaluate the effect of breast cancer screening. Only the first primary breast tumour was included in the evaluation. RESULTS: The second peak of incidence after the prevalent screening round was 45% higher than the incidences before the start of the screening. Also, the decrease in incidence of large and node positive tumours was interrupted. Compared with national detection rates, the number of screen detected cancers was lower before 1995 and higher after that year. After 1997, incidence decreased again of all breast cancers, but also of large and node positive tumours. The incidence of node positive tumours showed large fluctuations, probably due to the introduction of the sentinel node procedure and immunohistochemistry. In 1999, incidence of large tumours and node positive tumours was 18% and 28%, respectively, lower than before the start of the screening. CONCLUSIONS: An increase in the background incidences and improved detection in the screening programme most likely explain this trend. The improved detection after 1995, and the lower than desirable decrease in large tumours, indicate that the screening performance was not optimal before 1996. The incidence of node positive tumours cannot be used any more as an indicator of the success of the screening programme because of detection bias.

Aged↗
PubMed2006

A case-control study of farming and prostate cancer in African-American and Caucasian men.

OBJECTIVE: To determine the risk of prostate cancer associated with farming by duration, recency and specific activities among African-Americans and Caucasians. METHODS: This population-based case-control study had information on farming-related activities for 405 incident prostate cancer cases and 392 controls matched for age, race and region in South Carolina, USA, from 1999 to 2001. Cases with histologically confirmed, primary invasive prostate cancer who were aged between 65 and 79 years were ascertained through the South Carolina Central Cancer Registry. Appropriately matched controls were identified from the Health Care Financing Administration Medicare Beneficiary File. Data were collected using computer-assisted telephone interviewing, and adjusted odds ratios (aOR) were estimated using unconditional logistic regression. RESULTS: Farming was associated with increased risk of prostate cancer in Caucasians (aOR 1.8; 95% confidence interval (CI) 1.3 to 2.7) but not in African-Americans (aOR 1.0; 95% CI 0.6 to 1.6). Regarding specific farming activities, farmers who mixed or applied pesticides had a higher risk of prostate cancer (aOR 1.6; 95% CI 1.2 to 2.2). Increased risk of prostate cancer was observed only for those farming <5 years. CONCLUSIONS: Increased risk of prostate cancer for farmers in this study may be attributable to pesticide exposure. Racial differences in the association between farming and prostate cancer may be explained by different farming activities or different gene-environment interactions by race.

Black or African American↗
PubMed1993

The computer in the radiologist's office.

Today, the radiologist is able to equip his or her office with a powerful personal computer system equivalent to the large mainframe computers of just a few years ago. If funds permit, purchase of a 486 equivalent system with 200-300 Mbytes of hard-disk storage, 16 Mbytes of random access memory (RAM), a high-resolution color video card and monitor, and a laser printer is recommended. The practical uses for such a system are almost limitless and include word processing, spreadsheet and data-base management, telecommunications, multimedia presentations, business applications, teleradiology, resident and medical student education, and research applications. No matter how much one becomes involved in computer applications, it is essential to establish good habits for backing up critical data files and programs. Becoming familiar with computer technology is not easy at first. Finding a good computer buddy, taking simple night school courses, and reading computer articles and magazines are good ways to get started. Computers are wonderful devices. The day is fast approaching when they will become a necessary tool for every radiologist.

Microcomputers↗
PubMed2004

Preoperative percutaneous portal vein embolization: evaluation of adverse events in 188 patients.

PURPOSE: To retrospectively assess the frequency of adverse events related to percutaneous preoperative portal vein embolization (PPVE). MATERIALS AND METHODS: Institutional review board did not require its approval or patient informed consent for this study. The adverse events that occurred during PPVE or until planned hepatic surgery was performed or cancelled were retrospectively obtained from clinical, imaging, and laboratory data files in 188 patients (109 male and 79 female patients; mean age, 60 years; range, 16-78 years). Liver resection was planned for metastases (n = 137), hepatocarcinoma (n = 31), cholangiocarcinoma (n = 15), fibrolamellar hepatoma (n = 1), and benign disease (n = 4). PPVE was performed with a single-lumen 5-F catheter and a contralateral approach with n-butyl cyanoacrylate mixed with iodized oil as the main embolic agent. The rate of complications in patients with cirrhosis was compared with that in patients without cirrhosis by using the chi(2) test. RESULTS: Adverse events occurred in 24 (12.8%) of 188 patients, including 12 complications and 12 incidental imaging findings. Complications included thrombosis of the portal vein feeding the future remnant liver (n = 1); migration of emboli in the portal vein feeding the future remnant liver, which necessitated angioplasty (n = 2); hemoperitoneum (n = 1); rupture of a metastasis in the gallbladder (n = 1); transitory hemobilia (n = 1); and transient liver failure (n = 6). Incidental findings were migration of small emboli in nontargeted portal branches (n = 10) and subcapsular hematoma (n = 2). Among the 187 patients in whom PPVE was technically successful, there was a significant difference (P < .001) between the occurrence of liver failure after PPVE in patients with cirrhosis (five of 30) and those without (one of 157). Sixteen liver resections were cancelled due to cancer progression (n = 12), insufficient hypertrophy of the nonembolized liver (n = 3), and complete portal thrombosis (n = 1). CONCLUSION: PPVE is a safe adjuvant technique for hypertrophy of the initially insufficient liver reserve. Post-PPVE transient liver failure is more common in patients with cirrhosis than in those without cirrhosis.

Acrylates↗
PubMed1991

Diagnostic radiology peer review: a method inclusive of all interpreters of radiographic examinations regardless of specialty.

A proposed method of assessing the quality of diagnostic radiographic examinations includes peer review designed to evaluate physicians, including nonradiologists, involved in the performance and interpretation of such examinations. A pilot project evaluated this system with randomly selected Pennsylvania Blue Shield data files of 10 providers billing for chest radiography interpretations during the second quarter of 1989. Of the 98 chest radiographs reviewed blindly, all inadequately marked radiographs and incomplete written reports were produced by nonradiologists. Technical quality of images obtained by radiologists did not significantly differ from that of images obtained by nonradiologists (P = .189). All five interpretive errors that could have seriously affected the patient's health care were produced by nonradiologists (P = .019). Four of these serious errors were made by providers billing for fewer than 25 radiographs. While administrative and time cost limitations are obvious, this method of peer review encompasses all physicians billing for a particular radiographic service, irrespective of specialty.

Blue Cross Blue Shield Insurance Plans↗