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Biomedical subjects

J H Silber

Publications and source records attributed to J H Silber.

43 records · Page 3Linked to original sources
PubMed1990

Stature loss following skeletal irradiation for childhood cancer.

A model is presented to predict adult stature in children treated successfully for cancer outside the CNS. The model is based on radiation dose in Gray adjusted for location of therapy and attained stature (GALA); ideal adult stature (IAS), assuming the patient had not developed cancer, calculated by the Roche-Wainer-Thissen (RWT) method (which uses patient stature and weight before developing cancer, and parent stature data); a femur correction if both the acetabula or heads of both femurs were irradiated (FEMUR); and sex. The model was constructed using data from 49 patients with a mean time from completion of therapy to follow-up of 8.9 years (range, 3.3 to 15.4 years). Thirteen patients received no radiotherapy. All model coefficients were highly significant (P less than .001), and the model appears to be an excellent predictor of adult stature, with a multiple correlation coefficient of 0.84 (R2 = .74) between corrected adult stature (CAS) based on the most recent follow-up stature available for the patient projected to final adult stature, compared with the model's predicted adult stature (MPAS), based only on initial data at presentation and subsequent radiation treatment. Patients who did not receive radiotherapy did not have loss of stature, ie, there was no significant difference between IAS and CAS, (P less than .71; n = 13), but patients who received radiotherapy had shorter statures than would be expected from the healthy population model (P less than .0004; n = 36). The magnitude of the loss in stature appears to be well explained by the dose and location of radiation, the stature already achieved at the time of radiotherapy, along with IAS, FEMUR, and sex. We believe this model will help clinicians to predict the growth effects of radiotherapy in children with cancer not involving the CNS.

Acetabulum↗
PubMed1988

Marginal analysis applied to the dose-response curve.

To improve on drug dosage decisions, the method of "marginal analysis," traditionally found in the economics literature, is applied to the dose-response curve. Marginal analysis is first defined and explained, next the technique is redefined for the clinical setting of dose determination subject to drug efficacy and side effects, and finally an example using adjuvant adriamycin chemotherapy in osteosarcoma is presented. By not using "marginal analysis," clinicians may not be maximizing overall therapeutic success or patient survival. Implications for future clinical trials are discussed, and a suggestion for estimating dose-response is proposed. The technique described should be readily applicable to many dosing problems, and need not be restricted to chemotherapy dosing decisions.

Bone Neoplasms↗
PubMed1987

Forecasting asthmatic wheezing using temperature velocity.

A model was constructed to predict pediatric asthmatic wheezing visits to the emergency department. All wheezing visits to the Children's Hospital of Philadelphia Emergency Department were analyzed for 1982 and 1983, for ages two to 18. Nine thousand four hundred twenty-five visits fit the study requirements, 27% of the total number of emergency department visits for all causes. The a priori hypothesis used to construct the model was that temperature change, not absolute temperature, would be a good predictor of emergency department visits. Although not attempting to prove a cause-and-effect relationship, by studying temperature velocity (the rate of change of temperature) and the direction of change of temperature (a seasonal variable reflecting rising or falling temperature), a model was created that was highly significant (P less than 0.0001) and could explain 35% of the daily variation in asthmatic emergency department visits (R2 = 35%, r = 0.59). When weekly emergency department visits were analyzed, the model could explain 49% of the variation in the number of emergency department visits (R2 = 49%, r = 0.70). Carbon monoxide, barometric pressure, and relative humidity were also statistically significant predictors but were clinically insignificant, explaining only a few percentage points of the total variation. By taking advantage of the seasonal pattern of wheezing through the use of temperature velocity, predictive models for asthmatic wheezing can be greatly improved. They may also aid in planning emergency department staffing, and even help prevent emergency department visits by premedication or lifestyle change during high-risk periods.

Adolescent↗
PubMed1986

Exophthalmos caused by excessive fat: CT volumetric analysis and differential diagnosis.

CT has proven to be excellent in identifying orbital pathology responsible for proptosis. Occasionally, no discrete mass or extraocular muscle enlargement to explain the exophthalmos is found, only an appearance suggestive of an abnormal increase in orbital fat volume. Fifteen patients were studied with proptosis apparently resulting from increased orbital fat. Clinical follow-up revealed that four of them had Graves orbitopathy, unilateral in one; two had Cushing disease/syndrome; and nine were obese without endocrinopathy. The orbital volume and percentage orbital fat volume were measured by CT software analysis in these patients and in a control group of 16 patients without proptosis. Measurements of proptosis and thickness of the scalp fat pad at the inion level were also performed. Significantly greater values for orbital fat volume, percentage fat volume, and proptosis were found in the proptosis group compared with the control group. There was excellent correlation between proptosis and percentage fat volume, supporting the contention that increased orbital fat is responsible for the proptosis. The thickness of the scalp fat pad at the inion level was significantly greater in obese and Cushing patients than in control subjects, but the thickness was not significantly greater in Graves patients than in controls. Proptosis and inion fat were well correlated (r = 0.74) in the control and obese patients, which suggests a relation between general body fat and orbital fat volume.

Adipose Tissue↗
PubMed1985

Loss weighting and the human cost of experimentation.

This paper analyzes the dilemma faced by clinicians who must determine a proper sample size for a clinical trial. A large sample size may be used to ensure significant results. In so doing, many patients may be randomized to the wrong arm of a clinical trial. Alternatively, fewer patients may be used in a clinical trial, however, the resulting conclusions will be less certain, and future patients may be harmed by false conclusions. This study introduces a ratio of relative human cost or loss associated with a single present patient receiving incorrect therapy during the clinical trial to a single future patient given incorrect therapy after the trial is over. This "loss weighting" ratio can be estimated, the trade-off between present and future loss can be evaluated and the total loss from a clinical trial can be minimized. The resulting method, based on the loss weighting ratio, suggests an inverse relationship between the number of future patients potentially affected by a clinical trial and the size of desired type I and type II error. The conclusions derived from this paper can be incorporated easily into the current process of sample size determination. This is illustrated with examples from two well-known clinical trials.

Clinical Trials as Topic↗
PubMedDate not supplied

Increased cholecystectomy rate after the introduction of laparoscopic cholecystectomy.

OBJECTIVE: To examine if overall cost savings may fail to result from laparoscopic ("closed") cholecystectomy if it also results in an increased total rate of cholecystectomies or generates additional costs unassociated with the open procedure. OUTCOME MEASURES: Inpatient and outpatient expenditures, incidence rates, and length of inpatient stay data for 6909 health maintenance organization enrollees with gallbladder complaints were analyzed from 1988 through 1992 using claims data from a large, private practice-based health maintenance organization. RESULTS: The incidence of cholecystectomy and total health maintenance organization expenditures on gallbladder disease have increased since the introduction of laparoscopic closed cholecystectomy. The rate of cholecystectomy procedures per 1000 enrollees increased from 1.35 in 1988 to 2.15 in 1992 (P < .001). Total annual medical expenditures on gallbladder disease per 1000 enrollees (in 1992 dollars) rose 11.4% during the study period (P < .001), despite a concurrent 25.1% decline in the unit cost (physician and hospital cost) for cholecystectomy procedures (P < .001). During the same study period, no significant change was noted in the rate of appendectomy per 1000 enrollees (0.76 in 1988 to 0.73 in 1992), which is a measure of nonelective surgical care, or in the inguinal hernia repair rate (2.01 in 1988 to 2.19 in 1992), which has a physician and patient discretionary component similar to that of cholecystectomy. CONCLUSIONS: The introduction of laparoscopic gallbladder surgery resulted in rising rates of cholecystectomy for a population of patients in a private, independent practice-based health maintenance organization. Such a rise was not seen for hernia repair surgery or appendectomy. It seems that the use of laparoscopic cholecystectomy, a new technology touted as reducing health care costs, may result in an increased consumption of health care resources due to changes in the indications for gallbladder surgery.

Cholecystectomy↗