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Biomedical subjects

J E Till

Publications and source records attributed to J E Till.

At least 55 records · Page 3Linked to original sources
PubMed1990

Development of a method to estimate thyroid dose from fallout radioiodine in a cohort study.

A cohort of 4831 persons aged 11-18 y in 1965 was identified among students in the schools of Washington County, UT; Lincoln County, NV; and Graham County, AZ. These children who had potentially been exposed to radioiodine from atomic weapons test fallout from the Nevada Test Site during 1951-1962 were selected for participation in a study of thyroid disease. The entire cohort was first examined during 1965-1968 for thyroid abnormalities. A total of 3,085 of these people were again reexamined during 1985-1986 to determine any subsequent occurrence of thyroid disease. In order to determine the relationship of the radiation dose to the thyroid with incidence of thyroid disease, we have developed a suite of models to calculate estimates of the internal dose received by the thyroid from fallout radioiodines. For completeness, the exposure to the thyroid from external radiation is also estimated. Dose estimates are made specific to each individual in the study using individual residential histories, the locality-specific exposure rate and radionuclide deposition, descriptions of dairy management for identified milk producers, and the subjects' sources of foods and intake rates of milk and leafy vegetables determined by interview. Other data such as the relationship of radioiodine deposition to measured exposure rate, environmental transfer parameters, and age-dependent factors for the conversion of radioiodine intake to thyroid dose were taken from work of other investigators. Dairy management information, milk distribution practices, the milk source for each study subject, as well as age-specific intake rates of milk and leafy vegetables, were determined by interview.

Adolescent↗
PubMed1990

Individual external exposures from Nevada Test Site fallout for Utah leukemia cases and controls.

External gamma-ray exposures from fallout originating at the Nevada Test Site (NTS) have been assigned to 6,507 individual subjects (1,177 leukemia cases and 5,330 control subjects) who died as Utah residents between 1952 and 1981. Leukemia cases were identified, confirmed, and classified by cell type from the Utah Cancer Registry, Utah State vital records, and medical records. Residential histories were obtained from the Deceased Membership File (DMF) of the Church of Jesus Christ of Latter-day Saints (LDS), supplemented by information from the LDS Church Census Records that were taken in 1950, 1955, and 1960-62. Control subjects were selected randomly within age strata from the DMF and were frequency-matched to the cases by age at death and for sex. Individual radiation exposures were assigned as a function of residence location and time interval for each residence during the fallout period (1951-1958) using geographic exposure data taken from the literature. Temporal distribution of exposure for subjects who resided in more than one locality or who were born or died during the fallout period was determined from data of other investigators. Calculated gamma-ray exposures for each place of residence were summed for each subject to yield the exposure to fallout from the NTS.

Case-Control Studies↗
PubMed1990

Are we getting informed consent from patients with cancer?

We developed a consent form for a hypothetical trial and asked patients to underline information that was pertinent to their decision to accept or refuse to participate in the proposed trial. We also investigated whether patients correctly interpreted statements describing the probability of certain events occurring. Of the 50 patients, 74% did not indicate that both risks and benefits were pertinent. Of the 20 patients who would not enter the trial, 70% focused on risks of therapy only. In contrast, of the 30 who agreed to enter, only 33% focused entirely on risks, while 10% did not note potential for either benefit or risk. For each of four probability statements, patients chose one of four possible interpretations, only one of which was correct. Depending on the statement, between 26 and 54% of the interpretations were incorrect. It appears that many decisions regarding trial entry may be based upon incomplete or incorrect information.

Adult↗
PubMed1989

Exemplary family physicians and consultants: empirical definition of contemporary medical practice.

To identify the characteristics of exemplary family physicians and consultants, we interviewed 25 family physicians and 25 consultants (5 each in the specialties of internal medicine, obstetrics and gynecology, pediatrics, psychiatry and surgery) selected by their peers as being exemplary in their own practice setting. The results indicated that the participants had well-formulated concepts of exemplary practitioners, defining five main categories of performance: clinical competence, relationship with patients, availability, family physician-consultant relationship and a fifth category that included organizational ability and personality attributes. The family physicians and the consultants placed different values on these categories and indicated that these values might change under different clinical circumstances. Their concepts appear to be compatible with, but not restricted to, a model of contemporary medical practice based on an ethic specific to medicine.

Attitude of Health Personnel↗
PubMed1989

Measuring satisfaction with health care: a comparison of single with paired rating strategies.

One of the central problems in studies of patient satisfaction with health care is the development of reliable and valid methods to determine the relative importance of different aspects of health care. Two techniques, paired comparisons and rating on a visual analogue scale, were compared in terms of their consistency with logical assumptions, test-retest reliability, and convergent validity. Thirty women with breast cancer were asked to assess brief hypothetical scenarios describing out-patient clinic visits to a tertiary cancer care centre. Each scenario incorporated three variables related to satisfaction with care: staff attitude, control over treatment decisions, and continuity of medical supervision. The paired choice method showed marginally better reliability and logical consistency than the rating method. Of the three variables assessed, continuity of medical supervision was consistently ranked highest in importance, and control over treatment decisions lowest. These preference assessment techniques appear to be suitable for use in the development of patient satisfaction indices, and for studies designed to examine variations in the priority given to different aspects of satisfaction with care.

Attitude of Health Personnel↗
PubMed1989

Cancer patients: their desire for information and participation in treatment decisions.

The relationship between cancer patients' desire for information and their preference for participation in decision making has been examined. Approximately 77% of the 52 patients reported that they had participated in decision making to the extent that they wished, while most of the remaining 23% would have preferred an opportunity to have greater input. Although many of the patients actively sought information, a majority preferred the physician to assume the role of the primary decision maker. Ethically, the disclosure of information has been assumed to be necessary for autonomous decision making. Nevertheless, the results of this study indicate that patients may actively seek information to satisfy an as yet unidentified aspect of psychological autonomy that does not necessarily include participation in decision making.

Canada↗
PubMed1988

Modeling the outdoor environment--new perspectives and challenges.

Assessing risk from manmade and naturally occurring radionuclides in the environment has long been of primary interest in radiation protection. Early investigations and decisions relied on direct measurements of radiation in environmental media; however, these techniques were inadequate for determining exposure to humans and biota from very low levels of radiation and in predicting exposures from future releases. The Plowshare Program in 1957 investigated the use of nuclear explosives for peaceful purposes and created an immediate need for predicting the dispersion and ultimate fate of radionuclides that might be vented to the atmosphere or enter groundwater and expose man. As a result, modeling the behavior of radionuclides in the outdoor environment became a field of vigorous interest, merging disciplines of mathematics, biology and physics, among others. Environmental models and, more specifically, models predicting radiation dose from radionuclides in the environment have evolved rapidly and have increased significantly in sophistication, complexity and scope. Application of these models is commonly known as radiological assessment. This presentation examines the current status, future direction and weaknesses of radiological assessment models used in making decisions about radiation. The trend in recent years has been toward more complex models, which has not necessarily improved the accuracy of dose estimates and, in certain cases, has had the opposite effect. The presentation also discusses the future of model development, with particular emphasis on simple techniques and the expanded use of microcomputers, which will make radiological assessment models widely available for risk assessment and for practical applications such as the design of efficient monitoring programs and engineering calculations on the clean-up of contaminated soils. The screening models developed by the National Council on Radiation Protection and Measurements are offered as an example of a powerful yet simple method for demonstrating compliance with standards. Finally, the paper reviews two major areas of challenge for the future--defining uncertainty associated with radiological assessment models and the potential for converting radiological assessment models for use with nonradioactive environmental pollutants such as chemicals. Modeling radionuclides in the environment is adopting a new perspective. Future models will be less complex than their predecessors and will be adaptable to a much broader range of users. Key challenges remain in applying the techniques used for radionuclides to nonradioactive pollutants.

Air Pollutants, Radioactive↗
PubMed1988

A pathway analysis approach for determining acceptable levels of contamination of radionuclides in soil.

A methodology for determining acceptable levels for decontamination of soil containing radionuclides at waste sites is described. This methodology calculates the annual radiation dose that an individual receives while living on property that has been decommissioned and decontaminated. Pathways of exposure include direct radiation from ground surfaces, ingestion of contaminated food, inhalation of resuspended radionuclides and drinking contaminated water. Results calculated using this methodology were compared with U.S. Department of Energy (DOE) guidelines for a southeastern U.S. site. There is good agreement between the two methods provided similar assumptions are used.

Animals↗
PubMed1987

Eliciting preferences for alternative drug therapies in oncology: influence of treatment outcome description, elicitation technique and treatment experience on preferences.

Several methodologic issues arise in eliciting preferences for therapy. Examples are the selection of appropriate descriptions of treatment outcomes and of elicitation techniques. Of particular importance is the correspondence of patients' anticipated preferences for treatment to actual preferences once they have experienced treatment. Treatment outcome descriptions and elicitation techniques were compared for a hypothetical drug decision problem involving trade-offs between quality and quantity of life. Preferences of 54 cancer patients were elicited before, and 6 weeks following initiation of chemotherapy treatment. Patients' preferences were not influenced by the way information about side effects was presented, nor the stated probability of survival at high and moderate levels. A riskless rating technique produced different preferences from those of a risky treatment choice method. Although patients experienced significant toxicity following initiation of treatment, their preferences remained stable on retest. The results raise questions about the extent to which patients are willing, at the time of decision making, to trade off survival rate for improved quality of life.

Antineoplastic Agents↗
PubMed1987

Why are (or are not) patients given the option to enter clinical trials?

Much attention has been paid to the use of ethical principles to guide the conduct of clinical trials. Less has been done to clarify and assess the "weights" assigned by clinicians (and others) to the values that come into conflict when patients are offered entry into trials. Quantitative techniques of value assessment were used to measure the relative importance of variables frequently identified as barriers to the entry of patients into clinical trials. Responses were obtained from 52 oncologists, 26 clinical trials and senior nurses, and 23 family physicians. The group of oncologists identified the scientific design of the trial as the most important factor. In contrast, the groups of nurses and family physicians gave higher weight to effects of the trial on the doctor-patient relationship. The results illustrate ways in which methods of value assessment may be used to clarify and rank values.

Clinical Trials as Topic↗
PubMed1986

Multi-type Galton-Watson process as a model for proliferating human tumour cell populations derived from stem cells: estimation of stem cell self-renewal probabilities in human ovarian carcinomas.

A mathematical model for proliferation of tumour cell populations is developed. The cell population is assumed to be organized in a hierarchy of decreasing proliferative potential and increasing degree of differentiation. Using some elements of the theory of Multi-type Galton-Watson processes, a method is proposed for the estimation of Psr, the probability of self-renewal of tumour stem cells, from the experimental distribution of clonal unit sizes obtained in cell culture studies. Six data sets from patients with advanced adenocarcinoma of the ovary are used to demonstrate the method. Reasonable estimates are obtained, and the theoretical colony size distributions predicted by the model appear to be in good qualitative agreement with the experimental ones, and lend support to a stem cell model of tumour growth. The possible significance of Psr as a prognostic factor is briefly discussed.

Cell Division↗
PubMed1985

Eliciting preferences for alternative cancer drug treatments. The influence of framing, medium, and rater variables.

In oncology there is increasing interest in the development of techniques to help patients choose between alternative therapies in ways that are consistent with their preferences. The purpose of this study was to examine some methodological problems associated with the elicitation of preferences. Preferences for alternative drug therapies were sought from 208 visitors to an open house at the Ontario Cancer Institute and from 216 university nursing students. Preferences were not significantly dependent on the sex, age or professional status of the respondents, nor on the medium used for elicitation of preferences (computer terminal versus pencil-and-paper questionnaire). In contrast, the importance of the way decision problems are framed was confirmed. Comparison of a positive frame (outcomes expressed as the probability of surviving) with a negative frame (outcomes expressed as the probability of dying) and a mixed frame (probabilities of surviving and dying were both given) pointed to the presence or absence of the word "survive" in the outcome description as the main source of framing bias. The framing effect was in the opposite direction to that hypothesized.

Adolescent↗