Studies of the mortality among nuclear industry workforces have been carried out, and nationally combined analyses performed, in the U.S., the UK and Canada. This paper presents the results of ...internationally combined analyses of mortality data on 95,673 workers (85.4% men) monitored for external exposure to ionizing radiation and employed for 6 months or longer in the nuclear industry of one of the three countries. These analyses were undertaken to obtain a more precise direct assessment of the carcinogenic effects of protracted low-level exposure to external, predominantly γ, radiation. The combination of the data from the various studies increases the power to study associations between radiation and specific cancers. The combined analyses covered a total of 2,124,526 person-years (PY) at risk and 15,825 deaths, 3,976 of which were due to cancer. There was no evidence of an association between radiation dose and mortality from all causes or from all cancers. Mortality from leukemia, excluding chronic lymphocytic leukemia (CLL)-the cause of death most strongly and consistently related to radiation dose in studies of atomic bomb survivors and other populations exposed at high dose rates-was significantly associated with cumulative external radiation dose (one-sided P value = 0.046; 119 deaths). Among the 31 other specific types of cancer studied, a significant association was observed only for multiple myeloma (one-sided P value = 0.037; 44 deaths), and this was attributable primarily to the associations reported previously between this disease and radiation dose in the Hanford (U.S.) and Sellafield (UK) cohorts. The excess relative risk (ERR) estimates for all cancers excluding leukemia, and leukemia excluding CLL, the two main groupings of causes of death for which risk estimates have been derived from studies of atomic bomb survivors, were -0.07 per Sv 90% confidence interval (CI): -0.4, 0.3 and 2.18 per Sv (90% CI: 0.1, 5.7), respectively. These values correspond to a relative risk of 0.99 for all cancers excluding leukemia and 1.22 for leukemia excluding CLL for a cumulative protracted dose of 100 mSv compared to 0 mSv. These estimates, which did not differ significantly across cohorts or between men and women, are the most comprehensive and precise direct estimates of cancer risk associated with low-dose protracted exposures obtained to date. Although they are lower than the linear estimates obtained from studies of atomic bomb survivors, they are compatible with a range of possibilities, from a reduction of risk at low doses, to risks twice those on which current radiation protection recommendations are based. Overall, the results of this study do not suggest that current radiation risk estimates for cancer at low levels of exposure are appreciably in error.
Out of a consecutive series of 698 cases of squamous cell carcinomas of the tonsillar region treated by radical megavoltage radiotherapy, a determinate group of 465 cases remained eligible for a ...multivariate analysis of the pretreatment features of the disease and treatment-related parameters predictive of lasting control of the disease at the primary site. T-stage and initial site within the tonsillar region, were the significant pretreatment factors. Tumours arising from the glossopalatine sulcus which are characterized by involvement of the tongue, do significantly worse than those arising from other sites within the tonsillar region: i.e. the tonsil itself, posterior pillar and to a lesser extent the anterior pillar. As regards treatment-related parameters in the 465 cases which received tumour doses of at least 55 Gy, only the length of overall treatment time was found to be predictive. Combining both pretreatment and treatment variables, T-stage (p less than 0.0001), overall treatment time (p less than 0.0001) were by decreasing order of significance the predicting factors, followed by initial site (p = 0.006). When present, tumour extension to the anatomical structures anterior to the tonsillar region was also found to be significant (p = 0.05). Based on these factors, a multivariate model was constructed and tested by estimating the product-limit survival of the various categories of patients. Four groups are individualized with 3 years local control rates ranging from 90 to 21%. The predictive accuracy of the model was assessed by log-rank test significance levels. The model may help to select patients for whom conventional radical radiotherapy is inadequate, and combined modality or altered fractionation regimes should be tried particularly for advanced tumours of the glossopalatine sulcus, and any case with significant invasion of the oral cavity.
Summary
When setting standards for protection against ionising radiation it has been usual to extrapolate from experience with high-dose short-term exposure—studies based on atom bomb survivors and ...patients exposed to radiation therapeutically. Those who work in the nuclear industry are exposed to low-level predominantly γ radiation for longer periods, and provide an alternative direct source of information. We have combined mortality data from seven cohort studies on nearly 96 000 nuclear industry workers monitored for external radiation in Canada, UK, and USA to assess directly the carcinogenic effects of protracted low-dose exposure to ionising radiation.
The excess relative risk for death from leukaemia, excluding chronic lymphocytic leukaemia, was 2·2 per Sv (90% Cl 0·1 to 5·7). This estimate is intermediate between the linear estimate of 3·7 per Sv and the linear-quadratic estimate (as used in recent leukaemia risk assessments) of 1·4 per Sv derived from Japanese atomic bomb survivors' data. The excess relative risk for death from all cancers, excluding leukaemia, was -0·07 per Sv (90% Cl -0·4 to 0·3). This estimate is consistent with a range of risks varying from negative to nearly twice those estimated from atomic bomb survivors (0·18 per Sv).
These are the most precise direct estimates so far made of carcinogenic risk after protracted exposure to low-dose ionising radiation. They provide little evidence that the estimates that form the basis of current radiation protection recommendations are appreciably in error.
In 1987, most states raised the speed limit from 55 to 65 mph on portions of their rural interstate highways. There was intense debate about the increase, and numerous evaluations were conducted ...afterwards. These evaluations share a common problem: they only measure the local effects of the change. But the change must be judged by its system-wide effects. In particular, the new 65 mph limit allowed the state highway patrols to shift their resources from speed enforcement on the interstates to other safety activities and other highways--a shift many highway patrol chiefs had argued for. If the chiefs were correct, the new allocation of patrol resources should lead to a reduction in statewide fatality rates. Similarly, the chance to drive faster on the interstates should attract drivers away from other, more dangerous roads, again generating system-wide consequences. This study measures these changes and obtains surprising results. We find that the 65 mph limit reduced statewide fatality rates by 3.4% to 5.1%, holding constant the effects of long-term trend, driving exposure, seat belt laws, and economic factors.
Road pricing is widely advocated as a solution to congestion problems. The underlying theory is well developed, and we even have the technology to implement it without toll booths. Only political ...barriers remain: Decision makers are reluctant to retrofit tolls on existing highways because they do not know what circumstances might make such an action acceptable to the public. This paper develops a graphical model that displays the interaction between road capacity, user demand, travel speed and toll charges. The model is then used to analyze the sources of public resistance to road pricing. Might the potential response to road pricing be predicted using data from the new toll roads now being built around the United States? Our model shows it cannot: Political success depends on the demand characteristics at the right-hand side of the demand curve, while toll road data only trace out the left-hand side of the curve. Our model also shows situations where the new toll roads are likely to generate public anger. The Appendix discusses an experimental design that uses unobtrusive measures to assess the effect of a transportation project.
In a series of 1251 cases of squamous cell carcinomas of oropharynx and pharyngolarynx with clinically positive neck and treated primarily by radiation therapy a determinate group of 798 cases ...remained eligible for a multivariate analysis of the prognostic factors related to the regional outcome. Node size (p less than 0.0001), node fixity (p = 0.016) and T stage (p = 0.02) were the significant pretreatment factors independently predictive of neck node control. when regarding the treatment modalities in this determinate group of patients who received tumor doses of at least 55 Gy, only the treatment duration was found to be predictive (p = 0.002). Based on these factors, a multivariate model was constructed and tested by estimating the product-limit survival of the various groups of patients. The predictive accuracy of the equation was assessed by the log-rank test significance levels. The model may help to select, in many clinical situations, the appropriate approach of the management of metastatic neck disease, either by definitive radiation therapy or by combined modalities.
Recently, Bataini et al. reported that overall time was the major treatment-related determinant of local control in 465 squamous carcinomas of the tonsillar region. They did not, however, quantify ...the relationship or relate it to the doubling time of tumorigenic cells, except qualitatively. This note reports an attempt at that quantification.
We reviewed a series of 1,666 patients with squamous cell carcinoma of the oropharynx and pharyngolarynx treated with definitive radiation therapy to determine whether or not radioresponsiveness of ...the metastatic neck nodes is a reliable indicator of their radiocurability. In a determined group of 708 patients with clinically positive neck nodes, only one third of the adenopathies (247/759) completely regressed at the completion of the treatment. At 6 months, only ten percent of the nodes remained palpable. Lymph node clearance rates and halving diameter times were tumor size-dependent. Node clearance rate was also influenced by the site of the primary lesion. The impact of various parameters, both intrinsic and extrinsic to the tumor behavior, is discussed. Neck control probability was significantly higher for complete responders. In this group, the ultimate node control was as good for adenopathies larger than 6 cm as for the smaller ones. Tumor control probability directly related to clearance rate following radiotherapy. Finally, therapeutic implications are derived for nodal dose adjustments and optimal applicability of radiosurgical combinations.
In 1987 the U.S. government allowed states to raise speed limits to 65‐mph on some highways. We evaluate the consequences using a resource allocation perspective: the chance to drive faster ...reallocates traffic from side roads to the safer interstate highways, and a higher speed limit permits highway patrols to shift manpower from speed enforcement to other safety activities. This perspective implies that we should measure the effect of a speed limit by its systemwide rather than its local effects. We do so and find that the fatality rate dropped by 3.49%‐5.1% following the speed limit increase. (JEL A10, R40)
A Poet's "Education" Lave, Charles A.
Science (American Association for the Advancement of Science),
1979-Jan-19, Letnik:
203, Številka:
4377
Journal Article
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