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Risk estimation in radiation carcinogenesis depends primarily on epidemiological data and hazard rate models. The A-bomb survivors follow-up provides information on the complexity of this process. Several hazard rate models are briefly discussed and illustrated using the A-bomb experience.
We have reliable data on the degree of stenosis above which endarterectomy for symptomatic carotid stenosis is beneficial, but benefit is also influenced by other factors, particularly age, sex, the timing of surgery, plaque surface morphology and the nature of the presenting symptomatic event(s). This review will consider the selection of patients for carotid surgery based on the factors that influence the likely risk of stroke on medical treatment. In order to take into account all of the relevant factors, a risk prediction model is considered.
Severe thrombocytopenia is a rare but life-threatening side effect of cytotoxic chemotherapy for which risk factors are not well known. Our objective was to delineate a risk model for chemotherapy-induced thrombocytopenia requiring platelet transfusions in cancer patients. Univariate and multivariate analysis of risk factors for chemotherapy-induced thrombocytopenia requiring platelet transfusions were performed on the cohort of the 1,051 patients (CLB 1996) treated with chemotherapy in the Department of Medicine of the Centre Léon Bérard (CLB) in 1996. In univariate analysis, performance status (PS) greater than 1, platelet count less than 150, 000/microL at day 1 (d1) before the initiation of chemotherapy, d1 lymphocyte count < or = 700/microL, d1 polymorphonuclear leukocyte count less than 1,500/microL, and the type of chemotherapy (high risk v others) were significantly associated (P < .01) with an increased risk of severe thrombocytopenia requiring platelet transfusions. Using logistic regression, d1 platelet count less than 150,000/microL (odds ratio [OR], 4.3; 95% confidence interval [CI], 1.9 to 9.6), d1 lymphocyte counts < or = 700/microL (OR, 3.37; 95% CI, 1.77 to 6.4), the type of chemotherapy (OR, 3.38; 95% CI, 1.77 to 6.4), and PS greater than 1 (OR, 2.23; 95% CI, 1.22 to 4.1) were identified as independent risk factors for platelet transfusions. The observed incidences of platelet transfusions were 45%, 13%, 7%, and 1.5% for patients with > or = 3, 2, 1, or 0 risk factors, respectively. This model was then tested in 3 groups of patients treated with chemotherapy used as validation samples: (1) the series of 340 patients treated in the CLB in the first 6 months of 1997, (2) the prospective multicentric cohort of 321 patients of the ELYPSE 1 study, and (3) the series of 149 patients with non-Hodgkin's lymphoma treated in the CLB within prospective phase III trials (1987 to 1995). In these 3 groups, the observed incidences of platelet transfusions in the above-defined risk groups did not differ significantly (P > .1) from those calculated in the model. This risk index could be useful to identify patients at high risk for chemotherapy-induced thrombocytopenia requiring platelet transfusions.
The RESidual RADioactivity (RESRAD) computer code has been used for years to calculate carcinogenic risk and radiological dose from exposure to radionuclides. The basic ingestion, inhalation, and direct gamma intake equations used by RESRAD, Risk Assessment Guidance for Superfund (RAGS), and the Soil Screening Guidance for Radionuclides (SSG) are similar and can produce similar results, but there are some notable differences. Of particular interest is the fact that RESRAD incorporates sophisticated environmental transport models. Associated environmental parameters allow risk assessors to consider, among other variables, the size (i.e., surface area) of the contaminated zone, a variable not typically addressed quantitatively under the RAGS/SSG paradigm. Considering the similarities between basic RESRAD, RAGS, and SSG intake equations and given the broad acceptance of RESRAD, it stands to reason that RESRAD-derived area factors may be used to supplement RAGS/SSG human health risk calculations. This would allow risk assessors to retrofit existing results or otherwise modify standard RAGS/SSG equations for use in site closeout planning under the Multi-Agency Radiation Survey and Site Investigation Manual (MARSSIM), given a key component of the MARSSIM method is the consideration of small areas of elevated activity or "hot spots" through the use of area factors.
PURPOSE OF INVESTIGATION: The aim of the study was to devise a scoring system based on significantly prognostic parameters which might predict the survival time for each individual patient. METHODS: The study group included 40 patients with stage III or IV invasive ovarian cancer, operated on between 1987 and 1994. Different preoperative and intraoperative parameters were examined and their impact on survival was assessed using the Kaplan-Meier method. Survival rates were compared by the log rank test. The parameters, which have been found to be significant prognostic factors, were incorporated into the final risk model, based on a scoring system. The scores were given according to the cut-off point of each prognostic parameter. A correlation coefficient was calculated from the survival curve, representing the combined scores of individual patients versus their survival. RESULTS: From all studied parameters, only gravidity, the stage of ovarian cancer and the preoperative levels of LDH and CA-125 were demonstrated to have a significant impact on survival. On the basis of these four parameters a scoring system was devised. The scores were given considering the cut-off level of each parameter: gravidity < or = 2 versus > 2; stage of the cancer - IIIA, IIIB and stage IIIC versus stage IV; LDH level < or = 240 versus > 240 U/L; CA-125 < or = 100 versus > 100 U/ml. The average of the combined scores representing the four parameters was the final risk factor, which was plotted against the survival of each individual patient. A correlation coefficient of -0.99 was found. CONCLUSIONS: Our data suggest that the survival of each individual patient with advanced ovarian cancer could be predicted quite accurately considering our risk model based on a scoring system which incorporates four preoperative and intraoperative parameters. This scoring system needs to be validated by larger prospective trials.
When assessing the impact of radiation exposure it is common practice to present the final conclusions in terms of excess lifetime cancer risk in a population exposed to a given dose. The present investigation is mainly a methodological study focusing on some of the major issues and uncertainties involved in calculating such excess lifetime risks and related risk projection methods. The age-constant relative risk model used in the recent analyses of the cancer mortality that was observed in the follow-up of the cohort of A-bomb survivors in Hiroshima and Nagasaki is used to describe the effect of the exposure on the cancer mortality. In this type of model the excess relative risk is constant in age-at-risk, but depends on the age-at-exposure. Calculation of excess lifetime risks usually requires rather complicated life-table computations. In this paper we propose a simple approximation to the excess lifetime risk; the validity of the approximation for low levels of exposure is justified empirically as well as theoretically. This approximation provides important guidance in understanding the influence of the various factors involved in risk projections. Among the further topics considered are the influence of a latent period, the additional problems involved in calculations of site-specific excess lifetime cancer risks, the consequences of a leveling off or a plateau in the excess relative risk, and the uncertainties involved in transferring results from one population to another. The main part of this study relates to the situation with a single, instantaneous exposure, but a brief discussion is also given of the problem with a continuous exposure at a low-dose rate.
In this paper a more general competing risk model is developed for dealing with censored data with multiple outcomes, as the result of the competition with other risk factors. More reasonable results are obtained by applying the model in the probability and the average duration of pneumoconiosis progress from stage I to stage II in Shanxi Province.
In this paper, a new non-parametric competing-risk model is proposed. This model takes relative susceptibility into account, and is thus free from the usual assumption of independence between competing causes of death. Another feature of the model is the adjustments of survivors and deaths as a results of the elimination of one of the causes of death in the previous time interval. The computational procedure of the model is simple and can be incorporated into the regular life table procedures.
The potential contribution to U.S. lung cancer deaths from 1930 to 1987 from indoor 222Rn exposures is investigated from the standpoint of a constant relative risk model. Based on this model, which assumes a Rn risk proportional to the baseline lung cancer risk from other causes, the rate of Rn-induced lung cancer mortality has been increasing sharply since 1930. However, the estimated proportion of lung cancer deaths attributable to Rn has remained fairly constant. Applying the range of coefficients the U.S. Environmental Protection Agency employs in assessing the risk from indoor Rn, it is estimated that 8-25% of all current lung cancer deaths are "attributable to" past Rn exposures. The major sources of uncertainty in the estimates are discussed.
This study tested hypotheses derived from Wickramasekera's High Risk Model of Threat Perception (HRMTP) by comparing autonomic and affective responses to a cognitive and an emotional stress task in high, medium, and low hypnotizables. Electrodermal activity (EDA) was used as a measure of sympathetic activity, and the high frequency (HF) spectral component of heart rate variability as a measure of parasympathetic activity. High hypnotizables exhibited greater EDA at baseline and slower EDA recovery following both tasks than did medium and lows. Medium hypnotizables responded with greater decreases in normalized HF power than did highs and lows during the emotional stress task. The results suggest diminished EDA variability in high hypnotizables and the potential for HF power as an indicator of autonomic dysregulation in low and high hypnotizables, compared to mediums. The results are discussed in relation to predictions based on the HRMTP.
In the competing risks literature, one usually compares whether two risks are equal or whether one is "more serious." In this paper, we propose tests for the equality of two competing risks against an ordered alternative specified by their sub-survival functions. These tests are naturally developed as extensions of those based on hazard rates and cumulative incidence functions. We note that the interpretation of the new test results is more direct compared to the situation when the hypotheses are framed in terms of their cumulative incidence functions. The proposed tests are of the Kolmogrov-Smirnov type, based on maximum differences between sub-survival functions. Our simulation studies indicate that they are excellent competitors of the existing tests, that are based mainly on differences between cumulative incidence functions. A numerical example will demonstrate the advantages of the proposed tests.
We propose a method to estimate the regression coefficients in a competing risks model where the cause-specific hazard for the cause of interest is related to covariates through a proportional hazards relationship and when cause of failure is missing for some individuals. We use multiple imputation procedures to impute missing cause of failure, where the probability that a missing cause is the cause of interest may depend on auxiliary covariates, and combine the maximum partial likelihood estimators computed from several imputed data sets into an estimator that is consistent and asymptotically normal. A consistent estimator for the asymptotic variance is also derived. Simulation results suggest the relevance of the theory in finite samples. Results are also illustrated with data from a breast cancer study.
BACKGROUND: Carotid endarterectomy lowers the risk of carotid territory ipsilateral ischaemic stroke, and is the treatment of choice, in patients with recently symptomatic 70-99% carotid stenosis. However, the 3-year risk of stroke on medical treatment alone is only about 20%. We investigated whether the efficacy of endarterectomy would be improved if patients with a high risk of stroke on medical treatment and a low risk of operative stroke or death could be identified. METHODS: We developed two prognostic models from data on patients with 0-69% carotid stenosis in the European Carotid Surgery Trial (ECST). The medical model predicted risk of ipsilateral carotid territory major ischaemic stroke (fatal or lasting longer than 7 days) on medical treatment and the surgical model predicted risk of major stroke and death within 30 days of endarterectomy. From these models we developed a prognostic score to identify patients with a high risk of stroke on medical treatment but a low operative risk. We validated the models and tested the scoring system on 990 ECST patients with 70-99% carotid stenosis assigned surgery (594) or medical treatment only (396). FINDINGS: When patients with 70-99% stenosis were stratified by the scoring system, which was based on seven independent prognostic factors, endarterectomy was beneficial in only 162 (16%) patients. The 5-year absolute risk of carotid territory ipsilateral major ischaemic stroke, operative major stroke, or death was lowered by 33% in the 16% of patients with a score of 4 or more (odds ratio 0.12 [95% CI 0.05-0.29], p<0.0001), but not in the other 828 (84%) patients (1.00 [0.65-1.54], p=0.7). INTERPRETATION: Many patients with recently symptomatic 70-99% carotid stenosis may not benefit from carotid endarterectomy. Validation of the predictive score is needed on external datasets, but risk-factor modelling could be useful to identify those patients in whom endarterectomy will be beneficial.
The Framingham Heart Study has been the foundation upon which several national policies regarding risk factors for coronary heart disease mortality are based. The NHANES I Epidemiologic Followup Study is the first national cohort study based upon a comprehensive medical examination of a probability sample of United States adults. The average follow-up time was 10 years. This study afforded an opportunity to evaluate the generalizability of the Framingham risk model, using systolic blood pressure, total cholesterol, and cigarette smoking, to the U.S. population with respect to predicting death from coronary heart disease. The Framingham model predicts remarkably well for this national sample. The major risk factors for coronary heart disease mortality described in previous Framingham analyses are applicable to the United States white adult population.
The perioperative nurse has long been involved in wound classification, a variable historically used for analysis of surgical site infections. Now, with the development of more sophisticated surgical risk models, surveillance programs may calculate risk-specific surgical site infection rates. The understanding of these models is pertinent to the practice of the perioperative nurse.
AIMS: To compare the predictions of the Systematic Coronary Risk Evaluation (SCORE) high- and low-risk functions applied to a recent population study with observed cardiovascular disease (CVD) mortality estimated from annual official mortality statistics in Norway. METHODS: Data were obtained from large epidemiological surveys conducted in five Norwegian counties in 2000-2003. RESULTS: A total of 32 251 men and women were investigated (aged 30-31, 40-41, 45-46, and 59-61). For men aged >or=59, more than 75% qualified for preventive treatment by having a 10-year risk >or=5%. Few women and practically no men younger than 46 years can be considered at high risk according to the SCORE risk prediction models. For men, the high-risk function overestimated and the low-risk model underestimated the CVD mortality as compared to the 10-year risks calculated from official mortality statistics (1999-2003). For women, however, both functions underestimated mortality in young individuals, whereas in the elderly an overestimation was observed. CONCLUSIONS: The risk predictions depended strongly on age and gender. The SCORE high-risk function overestimates the risk of fatal CVD for men in Norway, and before implementation in clinical practice, proper adjustments to national levels are required.
BACKGROUND: Severe neutropenia, a common consequence of chemotherapy, may result in infectious complications and hospitalizations. Preventive treatment with colony-stimulating factors is limited because of the inability to predict which patients will develop neutropenic complications. To the authors' knowledge, the current study is the first large prospective validation of a risk model in patients with early-stage breast carcinoma. METHODS: Patients with Stage I-III breast carcinoma who were receiving adjuvant chemotherapy (n=624) were assigned to risk groups based on first-cycle absolute neutrophil count (ANC) nadirs of <0.5 x 10(9)/L. Filgrastim (a recombinant human granulocyte-colony-stimulating factor) was administered from Cycle 2 onward to high-risk patients. Dose intensity and rates of neutropenic complications, including febrile neutropenia and hospitalization resulting from it, were calculated for each group and compared. High-risk patients were matched by chemotherapy regimen, stage of disease, age, and baseline ANC to historic-control patients and outcomes were compared within the matched pairs. RESULTS: Both risk groups were found to have a similar proportion of patients receiving >85% of the dose intensity (95.8% vs. 94.4%). The rate of febrile neutropenia and hospitalization in the low-risk group (n=264) was 2.6% (95% confidence interval [95% CI], 0.7-4.5%) and 0.8 (95% CI, -0.3-1.9%), respectively. The high-risk group was 2.6 times more likely to receive a full dose of chemotherapy, but no higher risk of neutropenic complications was reported compared with the matched controls. CONCLUSIONS: The risk-related prophylactic administration of filgrastim facilitated the delivery of planned chemotherapy to the high-risk group of patients. However, further research is needed to confirm the results obtained in the current study in a randomized trial, if feasible, and in other chemotherapy and disease settings.
OBJECTIVE: The objective of the present analysis was to compare the performance of a lung resection mortality model developed by means of logistic regression and bootstrap analysis with that of multiple mortality models developed by using the traditional training-and-test method from the same dataset. METHODS: Eleven mortality models (1 developed by means of logistic regression and bootstrap validation and the other 10 developed by means of the traditional training-and-test random splitting of the dataset) were generated by the data of unit A (571 patients submitted to major lung resection). The performances of each of the 11 mortality models were then evaluated by assessing the distribution of the respective c-statistics in 1000 bootstrap samples derived from unit B (224 patients). RESULTS: The first model (logistic regression and bootstrap analysis) had good discrimination among the 1000 bootstrap external samples (c-statistics >0.7 in 80% of samples and >0.8 in 38% of samples). Among the 10 training-and-test models, only one model had a similar performance, whereas the others had a poorer discrimination. CONCLUSIONS: The traditional training-and-test method for risk model building proved to be unreliable across multiple external populations and was generally inferior to bootstrap analysis for variable selection in regression analysis. Therefore the use of bootstrap analysis must be recommended for every future model-building process.