Errors In Dose Estimates Research Articles

Use of the FBX dosimeter for the quality assurance of 60Co and high energy teletherapy machines by mail

The concentrations of the solutes in the standard FBX dosimeter were changed in order to reduce the rate of thermal oxidation of ferrous ions in the solution. The modified solution contained 10-4 mol dm-3 ferrous ions. 10-3 mol dm-3 benzoic acid and 5*10-5 mol dm-3 xylenol orange in 0.04 mol dm-3 aqueous aerated sulphuric acid. The rates of thermal oxidation of ferrous ions do not differ significantly when the solution is stored either in glass or polypropylene containers. The error due to the post-irradiation delay in dose estimation depends on the dose and a dose of about 5 Gy is most suitable. When the solution stored up to about one month before irradiation and about one month after irradiation, the error in dose estimation is less than +or-2%. The blank and the irradiated solutions should be stored in similar containers.

Recent Uses of Biological Data for the Evaluation of A-Bomb Radiation Dosimetry

Random errors in the DS86 radiation dose estimates used in the analysis of A-bomb survivor data are recognized to have an important impact upon estimates of the risk of late effects such as cancer. Little however is known for certain concerning the distribution of such random errors. This paper gives an overview of recent work at the Radiation Effects Research Foundation (RERF) using multivariate analysis of biological data, including acute effects of radiation exposure, late effects (eg leukemia mortality) and stable chromosome aberrations, for the purpose of evaluating the extent of random error in the estimation of individual doses using DS86. The emphasis here is on analyses of apparent association between biological endpoints, in light of a dosimetry error model framework proposed recently by Pierce et al. Analyses performed to date appear to be consistent with the view that lognormal random dosimetry errors with a standard deviation of 40% or greater of true dose may exist in DS86. Association between radiogenic outcomes in A-bomb survivors, after adjustment for DS86 estimated dose level, has been detected for such widely varying pairs of outcomes as mutant T-cell frequencies and chromosome aberrations, epilation and leukemia mortality, and epilation and chromosome aberrations. The motivation for examining association between pairs of biological endpoints has usually been to determine the extent to which radiation sensitivity varies between individual survivors. Recognizing, however, that random error in dose estimates results in apparent association between biological outcomes is crucial to interpreting studies, such as these, which use data on multiple biological endpoints. To go one step further, in situations where there is a prior knowledge about the biological plausibility of such associations in outcome data the amount of association between radiogenic outcomes (remaining after adjustment for estimated dose), to the extent that they are greater than that assumed to be reasonable, is an important potential source of information concerning the magnitude of random errors in the DS86 dose estimates.

Allowing for Dose-Estimation Errors for the A-Bomb Survivor Data

Unless allowances are made, random errors in radiation dose estimates cause underestimation of linear risk estimates and distort the shape of dose-response curves. These errors also result in spurious associations between radiogenic endpoints, exaggerating possible variations in individual sensitivity to radiation. Statistical methods have been developed which reduce these biases, based on assumptions regarding the nature and magnitude of dose-estimation errors. Some understanding of the underlying statistical basis for these methods is necessary to both those interested in interpreting radiogenic effects and those interested in the dosimetry system. This paper discusses the basic statistical issues and their implications, presents some statistical methods to deal with the problem, and indicates the sensitivity of certain results to assumptions about the magnitude of the dose-estimation errors.

Allowing for Random Errors in Radiation Dose Estimates for the Atomic Bomb Survivor Data

The presence of random errors in the individual radiation dose estimates for the A-bomb survivors causes underestimation of radiation effects in dose-response analyses, and also distorts the shape of dose-response curves. Statistical methods are presented which will adjust for these biases, provided that a valid statistical model for the dose estimation errors is used. Emphasis is on clarifying some rather subtle statistical issues. For most of this development the distinction between radiation dose and exposure is not critical. The proposed methods involve downward adjustment of dose estimates, but this does not imply that the dosimetry system is faulty. Rather, this is a part of the dose-response analysis required to remove biases in the risk estimates. The primary focus of this report is on linear dose-response models, but methods for linear-quadratic models are also considered briefly. Some plausible models for the dose estimation errors are considered, which have typical errors in a range of 30-40% of the true values, and sensitivity analysis of the resulting bias corrections is provided. It is found that for these error models the resulting estimates of excess cancer risk based on linear models are about 6-17% greater than estimates that make no allowance for dose estimation errors. This increase in risk estimates is reduced to about 4-11% if, as has often been done recently, survivors with dose estimates above 4 Gy are eliminated from the analysis.

ＣＲ‐３９プラスチック中の粒子飛跡のエッチング特性

In using CR-39 plastics for individual neutron dosimeters, changes of etching efficiency cause significant error in dose estimation. Etching efficiency is subject to a number of parameters. In this study the influences of the parameters were examined by measuring the diameters of etch-pits formed by alpha-particles and enlarged by aqueous solutions of 25-35% KOH at 55-65°C for 4hr. It has been observed that diameter changes at the rate of 8.3%/°C in temperature, 8.2%/wt% in concentration and -0.60%/day in time after preparation of etchant. The diameter is unaffected by the supplying of up to 280ml/l, of distilled water for evaporation of etchant or by increase up to 5g/l of CR-39 dissolved in etchant. The magnitude of possible error has been estimated by parameter as well as ingeneral, so as to obtain suggestions for improving etching treatment.

Effects of contaminant radioactivity on results of 125I-radioligand assay.

Diagnostic radionuclide imaging procedures are often used in patients whose sera are later assayed by use of 125I-labeled radioligands; thus, it is important to identify those assays that potentially may be affected by contaminating radioactivity. Results obtained with assays in which specific separation methods (solid-phase primary antibody, second antibody) or small (10--25 micdo L) sample volumes are used are little affected by the presence of such contaminating radioactivity. Less-specific techniques (polyethylene glycol, charcoal, ion-exchange resin) segregate some of the contaminant activity into the bound fraction. The degree to which such activity is protein bound and the concentration of endogenous ligand then contribute to the resulting error in dose estimation. Samples for these assays should be screened for radioactivity before the assay is begun. Inclusion of nonspecific binding tubes for patients' samples when contamination is present permits the contaminating radioactivity to be evaluated and the patient's dose concentration to be more accurately estimated.