PubMed Health⌕ Search

Biomedical subjects

T H Wagner

Publications and source records attributed to T H Wagner.

At least 19 recordsLinked to original sources
PubMed2005

The use of megavoltage CT (MVCT) images for dose recomputations.

Megavoltage CT (MVCT) images of patients are acquired daily on a helical tomotherapy unit (TomoTherapy, Inc., Madison, WI). While these images are used primarily for patient alignment, they can also be used to recalculate the treatment plan for the patient anatomy of the day. The use of MVCT images for dose computations requires a reliable CT number to electron density calibration curve. In this work, we tested the stability of the MVCT numbers by determining the variation of this calibration with spatial arrangement of the phantom, time and MVCT acquisition parameters. The two calibration curves that represent the largest variations were applied to six clinical MVCT images for recalculations to test for dosimetric uncertainties. Among the six cases tested, the largest difference in any of the dosimetric endpoints was 3.1% but more typically the dosimetric endpoints varied by less than 2%. Using an average CT to electron density calibration and a thorax phantom, a series of end-to-end tests were run. Using a rigid phantom, recalculated dose volume histograms (DVHs) were compared with plan DVHs. Using a deformed phantom, recalculated point dose variations were compared with measurements. The MVCT field of view is limited and the image space outside this field of view can be filled in with information from the planning kVCT. This merging technique was tested for a rigid phantom. Finally, the influence of the MVCT slice thickness on the dose recalculation was investigated. The dosimetric differences observed in all phantom tests were within the range of dosimetric uncertainties observed due to variations in the calibration curve. The use of MVCT images allows the assessment of daily dose distributions with an accuracy that is similar to that of the initial kVCT dose calculation.

Algorithms↗
PubMed2005

Evaluation of a diode array for QA measurements on a helical tomotherapy unit.

A helical tomotherapy system is used in our clinic to deliver intensity-modulated radiation therapy (IMRT) treatments. Since this machine is designed to deliver IMRT treatments, the traditional field flatness requirements are no longer applicable. This allows the unit to operate without a field flatness filter and consequently the 400 mm wide fan beam is highly inhomogeneous in intensity. The shape of this beam profile is mapped during machine commissioning and for quality assurance purposes the shape of the beam profile needs to be monitored. The use of a commercial diode array for quality assurance measurements is investigated. Central axis beam profiles were acquired at different depths using solid water built-up material. These profiles were compared with ion chamber scans taken in a water tank to test the accuracy of the diode array measurements. The sensitivity of the diode array to variations in the beam profile was checked. Over a seven week period, beam profiles were repeatedly measured. The observed variations are compared with those observed with an on-board beam profile monitor. The diode measurements were in agreement with the ion chamber scans. In the high dose, low gradient region the average ratio between the diode and ion chamber readings was 1.000 +/- 0.005 (+/- 1 standard deviation). In the penumbra region the agreement was poorer but all diodes passed the distance to agreement (DTA) requirement of 2 mm. The trend in the beam profile variations that was measured with the diode array device was in agreement with the on-board monitor. While the calculated amount of variation differs between the devices, both were sensitive to subtle variations in the beam profile. The diode array is a valuable tool to quickly and accurately monitor the beam profile on a helical tomotherapy unit.

Evaluation Studies as Topic↗
PubMed2001

The demand for consumer health information.

Using data from an evaluation of a community-wide informational intervention, we modeled the demand for medical reference books, telephone advice nurses, and computers for health information. Data were gathered from random household surveys in Boise, ID (experimental site), Billings, MT, and Eugene, OR (control sites). Conditional difference-in-differences show that the intervention increased the use of medical reference books, advice nurses, and computers for health information by approximately 15, 6, and 4%. respectively. The results also suggest that the intervention was associated with a decreased reliance on health professionals for information.

Adolescent↗
PubMed2001

Does willingness to pay vary by race/ethnicity? An analysis using mammography among low-income women.

As part of a population-based intervention to improve periodic mammogram screening, we examined WTP for mammography in five ethnic groups. Through random digit dialing, we contacted households in low-income census tracts of Alameda County, California (San Francisco Bay area). Women who met the ethnicity, age and cancer-free eligibility criteria were invited to participate. For the baseline assessment, women were surveyed over the phone in their preferred language. Of the 1465 surveyed women, 499 identified themselves as African-American, 199 were Chinese, 167 were Filipino, 300 were Latina, and 300 were non-Hispanic white. Bivariate and multivariate analysis showed that WTP varied significantly by ethnicity (P<0.05). We also found that when Filipino and Chinese women had a female relative with breast cancer, they were willing to pay less money for a mammogram. African-American, Latino, and non-Hispanic white women, however, were willing to pay more money for a mammogram if a female relative had had breast cancer. This ethnic difference, when there is a familial link to breast cancer, needs further study as it has implication for genetic testing. Nevertheless, WTP studies that do not account for ethnic differences may be overstating net benefits to society.

California↗
PubMed2001

Isotropic beam bouquets for shaped beam linear accelerator radiosurgery.

In stereotactic radiosurgery and radiotherapy treatment planning, the steepest dose gradient is obtained by using beam arrangements with maximal beam separation. We propose a treatment plan optimization method that optimizes beam directions from the starting point of a set of isotropically convergent beams, as suggested by Webb. The optimization process then individually steers each beam to the best position, based on beam's-eye-view (BEV) critical structure overlaps with the target projection and the target's projected cross sectional area at each beam position. This final optimized beam arrangement maintains a large angular separation between adjacent beams while conformally avoiding critical structures. As shown by a radiosurgery plan, this optimization method improves the critical structure sparing properties of an unoptimized isotropic beam bouquet, while maintaining the same degree of dose conformity and dose gradient. This method provides a simple means of designing static beam radiosurgery plans with conformality indices that are within established guidelines for radiosurgery planning, and with dose gradients that approach those achieved in conventional radiosurgery planning.

Dose-Response Relationship, Radiation↗
PubMed2001

Does providing consumer health information affect self-reported medical utilization? Evidence from the Healthwise Communities Project.

OBJECTIVE: To determine whether providing health information to residents of Boise ID had an effect on their self-reported medical utilization. RESEARCH DESIGN: The Healthwise Communities Project (HCP) evaluation followed a quasi-experimental design. SUBJECTS: Random households in metropolitan zip codes were mailed questionnaires before and after the HCP. A total of 5,909 surveys were returned. MEASURES: The dependent variable was self-reported number of visits to the doctor in the past year. A difference-in-differences estimator was used to assess the intervention's community-level effect. We also assessed the intervention's effect on the variance of self-report utilization. RESULTS: Boise residents had a higher adjusted odds of entering care (OR = 1.27, 95% CI 0.88, 1.85) and 0.1 more doctor visits compared with residents in the control cities; however, for both outcomes, the effects were small and not significant. Although the means changed little, the data suggest that the variance of utilization in Boise decreased. CONCLUSIONS: The HCP had a small effect on overall self-reported utilization. Although the findings were not statistically significant, a posthoc power analysis revealed that the study was underpowered to detect effects of this magnitude. It may be possible to achieve larger effects by enrolling motivated people into a clinical trial. However, these data suggest that population-based efforts to provide health information have a small effect on self-reported utilization.

Adult↗
PubMed2001

When parents are given greater access to health information, does it affect pediatric utilization?

OBJECTIVE: Most studies assessing the effects of consumer health information on medical utilization have used randomized controlled clinical trials with the chronically ill. In this paper, we analyze the effect of the Healthwise Communities Project, a natural experiment that provided free self-care resources, on reported pediatric utilization. RESEARCH DESIGN: Random household surveys were collected before and after the intervention in Boise, Idaho and in two control communities. SUBJECTS: A total of 5,909 surveys were completed, representing an overall response rate of 54%. Of these, 1,812 respondents were between 18 and 55 years of age and had children under 18 years of age living in the home. All analyses were restricted to these 1,812 persons. MEASURES: Parents were asked how many times their children visited a physician in the last year. Responses were gathered with a categorical response scale, which was then transformed into a continuous variable (number of pediatric visits). RESULTS: The intervention was associated with a decrease in reported pediatric utilization rates. The decrease in visits ranged from -0.72 to -0.66 (P approximately 0.05), depending on the statistical model used. Further analyses of 423 families followed over time found a more modest decrease (-0.19) that was not statistically significant. CONCLUSIONS: This study found that increasing access to self-care books, telephone advice nurses, and Internet-based health information is associated with decreases in reported pediatric utilization. However, the significance of the results was sensitive to the statistical model. More research is needed to understand the average and marginal costs of providing health information to consumers.

Adult↗
PubMed2001

Who uses self-care books, advice nurses, and computers for health information?

OBJECTIVES: While evaluating the effect of a community-wide informational intervention, this study explored access, health, and demographic factors related to the use of medical reference books, telephone advice nurses, and computers for health information. METHODS: A random sample of households in the intervention city (Boise, Idaho) and two control cities were surveyed about their use of health information in 1996. Shortly thereafter, the Healthwise Communities Project (HCP) distributed health information to all Boise residents. A follow-up survey was conducted in 1998. Overall, 5,909 surveys were completed for a 54% response rate. RESULTS: The HCP intervention was associated with statistically significant increases in the use of medical reference books and telephone advice nurses. The increased use of computers for health information was marginally significant. Few access, health, or demographic factors were consistently associated with using the different resources, except that people with depression used more of all three information resources, and income was not a significant predictor. CONCLUSION: Providing free health information led to an increase in use, but access, health, and demographic factors were also important determinants. In particular, poor health status and presence of a chronic illness were associated with health information use. These results suggest that healthy consumers are less interested in health information, and it may take other incentives to motivate them to learn about prevention and healthy behaviors.

Adult↗
PubMed2000

A geometrically based method for automated radiosurgery planning.

PURPOSE: A geometrically based method of multiple isocenter linear accelerator radiosurgery treatment planning optimization was developed, based on a target's solid shape. METHODS AND MATERIALS: Our method uses an edge detection process to determine the optimal sphere packing arrangement with which to cover the planning target. The sphere packing arrangement is converted into a radiosurgery treatment plan by substituting the isocenter locations and collimator sizes for the spheres. RESULTS: This method is demonstrated on a set of 5 irregularly shaped phantom targets, as well as a set of 10 clinical example cases ranging from simple to very complex in planning difficulty. Using a prototype implementation of the method and standard dosimetric radiosurgery treatment planning tools, feasible treatment plans were developed for each target. The treatment plans generated for the phantom targets showed excellent dose conformity and acceptable dose homogeneity within the target volume. The algorithm was able to generate a radiosurgery plan conforming to the Radiation Therapy Oncology Group (RTOG) guidelines on radiosurgery for every clinical and phantom target examined. CONCLUSIONS: This automated planning method can serve as a valuable tool to assist treatment planners in rapidly and consistently designing conformal multiple isocenter radiosurgery treatment plans.

Algorithms↗
PubMed2000

Image localization for frameless stereotactic radiotherapy.

PURPOSE: Infrared light-emitting diodes (IRLEDs) have been used for optic-guided stereotactic radiotherapy localization at the University of Florida since 1995. The current paradigm requires stereotactic head ring placement for the patient's first fraction. The stereotactic coordinates and treatment plan are determined relative to this head ring. The IRLEDs are attached to the patient via a maxillary bite plate, and the position of the IRLEDs relative to linac isocenter is saved to file. These positions are then recalled for each subsequent treatment to position the patient for fractionated therapy. The purpose of this article was to report a method of predicting the desired IRLED locations without need for the invasive head ring. METHODS AND MATERIALS: To achieve the goal of frameless optic-guided radiotherapy, a method is required for direct localization of the IRLED positions from a CT scan. Because it is difficult to localize the exact point of light emission from a CT scan of an IRLED, a new bite plate was designed that contains eight aluminum fiducial markers along with the six IRLEDs. After a calibration procedure to establish the spatial relationship of the IRLEDs to the aluminum fiducial markers, the stereotactic coordinates of the IRLED light emission points are determined by localizing the aluminum fiducial markers in a stereotactic CT scan. RESULTS: To test the accuracy of direct CT determination of the IRLED positions, phantom tests were performed. The average accuracy of isocenter localization using the IRLED bite plate was 0.65 +/- 0. 17 mm for these phantom tests. In addition, the optic-guided system has a unique compatibility with the stereotactic head ring. Therefore, the isocentric localization capability was clinically tested using the stereotactic head ring as the absolute standard. The ongoing clinical trial has shown the frameless system to provide a patient localization accuracy of 1.11 +/- 0.3 mm compared with the head ring. CONCLUSION: Optic-guided radiotherapy using IRLEDs provides a mechanism through which setup accuracy may be improved over conventional techniques. To date, this optic-guided therapy has been used only as a hybrid system that requires use of the stereotactic head ring for the first fraction. This has limited its use in the routine clinical setting. Computation of the desired IRLED positions eliminates the need for the invasive head ring for the first fraction. This allows application of optic-guided therapy to a larger cohort of patients, and also facilitates the initiation of extracranial optic-guided radiotherapy.

Algorithms↗
PubMed2000

Willingness to pay for mammography: item development and testing among five ethnic groups.

The goal of this study was to develop a willingness to pay (WTP) question for mammography that is appropriate for low income, ethnically-diverse women. Through qualitative research with 50 low income women of five ethnic groups we developed both a WTP question and a willingness to travel question (WTT). After being refined through interviews with 41 women, these questions were pilot tested on a random sample of 52 low income, ethnically-diverse women in the San Francisco area. Results show that the concepts underlying WTP and WTT were culturally appropriate to the five ethnicities in this study. Analyses generally confirm the validity of the WTP and WTT questions. As expected, WTP was associated with household income, perceived risk of cancer, and knowledge that one needs a mammogram even after a clinical breast examination. Despite the small samples, WTP varied among the ethnic groups. Additionally, WTT was moderately correlated with the natural log of WTP (r = 0.58, P < 0.001). These questions are now in use in a larger clinical trial and future analyses will explore willingness to pay and willingness to travel within and across the ethnic groups.

Breast Neoplasms↗
PubMed2000

Health services utilization among Latinos and white non-Latinos: results from a national survey.

Utilization patterns may be changing as managed care organizations actively market services to Latinos. This study compares use of any care, emergency services, inpatient hospitalization, nonemergency outpatient care only, and preventive care among 1,001 self-identified Latino and 1,107 white non-Latino adults. Data were from the 1994 Commonwealth Fund Survey of Minority Health. Latinos were less likely than white non-Latinos to have entered the health system for any type of care, to have been admitted to a hospital, or to have used preventive care. Access to a regular source of care along with financial factors reduced the ethnic/racial gap in the use of any care and preventive care, yet cultural and behavioral factors contributed little. Latinos in managed care plans, compared with fee-for-service systems, were twice as likely to receive preventive care. This suggests that managed care has the potential to reduce inequities in preventive care utilization.

Adolescent↗
PubMed2000

Healthcare utilization among Hispanics: findings from the 1994 Minority Health Survey.

OBJECTIVE: To assess the effects of health need, enabling factors, and predisposing factors on entry into any type of care, volume of care, use of emergency services, hospitalization, and receipt of preventive services. STUDY DESIGN: Multiple regression analysis with cross-sectional data. PATIENTS AND METHODS: Participants were the 1001 adults who identified themselves as Hispanic in the Commonwealth Fund Minority Health Survey; a telephone survey of noninstitutionalized persons designed to oversample minorities was conducted. RESULTS: The 3 Hispanic subpopulations had similar sociodemographic profiles and similar patterns of healthcare utilization, except that Hispanics of other national origins were more likely to use preventive care compared with Mexican Americans and Puerto Ricans. Overall, 78% of the Hispanics surveyed entered the healthcare system in the past year, making an average of 5.25 visits. After controlling for other factors, immigrants had fewer visits and were less likely to have received preventive care. A regular source of care and insurance coverage influenced entry and volume of care, but was not associated with emergency services or hospitalizations. CONCLUSIONS: Access to care for Hispanics remains a major problem, significantly affected by structural and financial factors, personal experiences with the healthcare system, and predisposing factors. Policy solutions that address the health service needs of the uninsured will largely benefit Hispanics. In addition, as managed care plans compete for contracts and become more multicultural, access to care for Hispanics, including the uninsured, may improve through market forces.

Adolescent↗
PubMed2000

Economic considerations in overactive bladder.

Many costs are associated with overactive bladder (OAB). They include direct costs, such as those associated with treatment, diagnosis, routine care, and the consequences of the disease; indirect costs of lost wages and productivity; and intangible costs associated with pain, suffering, and decreased quality of life. Quantification of all these costs is essential for establishing the total economic burden of a disease on society. Currently, the total economic burden of OAB is unknown. However, various studies have determined that the economic burden of urinary incontinence, one of the symptoms of OAB, is substantial. It is also important to establish the economic impact of various interventions for OAB. Cost-minimization, cost-outcome, cost-utility, and cost-benefit models can be used for these analyses. The most difficult aspect of evaluating the economic impact of a treatment is estimating the intangible costs.

Cost Allocation↗
PubMed1999

Quality of life of women with urinary incontinence: further development of the incontinence quality of life instrument (I-QOL)

OBJECTIVES: To report on the further development of the Incontinence Quality of Life Instrument (I-QOL), a self-report quality of life measure specific to urinary incontinence (UI), including its measurement model, responsiveness, and effect size. METHODS: Incontinent female patients (141 with stress, 147 with mixed UI) completed the I-QOL and comparative measures at screening, pretreatment, and four subsequent follow-up visits during participation in a multicenter, double-blind, placebo-controlled, randomized trial assessing the efficacy of duloxetine. Psychometric testing followed standardized procedures. RESULTS: Factor analysis confirmed an overall score and three subscale scores (avoidance and limiting behaviors, psychosocial impacts, and social embarrassment). All scores were internally consistent (alpha = 0.87 to 0.93) and reproducible (ICC = 0.87 to 0.91). The pattern of previously reported correlations with the Short-Form 36-item Health Survey and Psychological Well-Being Schedule were confirmed. Responsiveness statistics using changes in the independent measures of stress test pad weight, number of incontinent episodes, and patient global impression of improvement ranged from 0.4 to 0.8. Minimally important changes ranged from 2% to 5% in association with these measures and effect sizes. CONCLUSIONS: In a clinical trial, the I-QOL proved to be valid, reproducible, and responsive to treatment for UI in women.

Adolescent↗
PubMed1998

Economic costs of urinary incontinence in 1995.

Urinary incontinence imposes a significant financial burden on individuals, their families, and healthcare organizations. For individuals 65 years of age and older these costs are substantial, increasing from $8.2 billion (1984 dollars) to $16.4 billion (1993 dollars). Both of these cost-of-illness estimates, however, relied on data and factors that have changed over time. This study updates these cost estimates. The 1995 societal cost of incontinence for individuals aged 65 years and older was $26.3 billion, or $3565 per individual with urinary incontinence. Limitations, implications, and directions for future research are also discussed.

Cost of Illness↗
PubMed1998

The effectiveness of mailed patient reminders on mammography screening: a meta-analysis.

BACKGROUND: Researchers have tried to increase mammography screening rates by using patient-oriented reminders. This paper compares the effectiveness of mailed patient reminders at increasing mammography screening. METHODS: Sixteen published articles met the inclusion criteria and were included in the meta-analysis. To assess the association between reminders and mammography screening, the Mantel-Haenszel odds ratio (OR) was calculated. RESULTS: Among U.S. studies in which controls did not receive any type of reminder, women who received reminders were approximately 50% more likely to get a mammogram (OR 1.48; chi(2)MH(1) = 38.27, P < .001). In addition, tailored letters were found to be more effective than generic reminders (OR 1.87; chi(2)MH(1) = 4.70, P < .05). Combining cost and effectiveness data allowed for estimates of cost per woman screened, which ranged from $0.96 to $5.88. CONCLUSIONS: Patient reminders are effective at increasing mammography screening. More research is needed to assess (1) the cost-effectiveness of patient reminders and (2) their effectiveness across race, education, income, and type of insurance.

Breast Neoplasms↗