Did the 65 mph speed limit save lives?

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.

Is reseeding from the primary a plausible cause of node failure?

In a previous analysis of node failures in 1251 consecutive patients with node positive oropharyngeal and pharyngolaryngeal squamous cell carcinomas treated by external radiotherapy alone at the Institut Curie, the main reasons for patient exclusion were node recurrence associated with primary failure (N+T failures) and doses less than 55 Gy. These exclusions reduced the number of node failures from 399/1251 (32%) to 77/798 (10%). Multivariate analysis of node recurrence indicated that node size and fixity, treatment duration, and T stage of primary were significant (higher probability of isolated node failure for the T1-T2 primaries). In the present analysis, it is noted that 60% of the N+T failures were observed less than 1 month after the completion of the irradiation and, therefore, were not likely the result of reseeding from the primary tumor. When all 1251 patients were included in the analysis, the probability of nodal failure increased for larger nodes, T4 primaries, lower nodal doses, presence of contralateral node metastases, and nodal fixation to the surrounding structures. No influence of the primary site was found. Treatment duration was closely associated with total dose to the nodes. The best description of the data was obtained with a model including total dose and not treatment time. However, as in the previous analysis, the exclusion of low-dose (less than 55 Gy) treatments resulted in the loss of a significant dose-control relationship. We conclude that the majority of node failures is unlikely to result from reseeding from the primary tumor, and therefore should not be excluded from local-control analyses. From a more radiobiological point of view, the exclusion of palliative treatments is questionable when studying the effect of dose on local control.

Further analysis of the time factor in squamous cell carcinoma of the tonsillar region.

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.

A multivariate primary tumour control analysis in 465 patients treated by radical radiotherapy for cancer of the tonsillar region: clinical and treatment parameters as prognostic factors.

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.

Primary radiotherapy of squamous cell carcinoma of the oropharynx and pharyngolarynx: tentative multivariate modelling system to predict the radiocurability of neck nodes.

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.

Impact of neck node radioresponsiveness on the regional control probability in patients with oropharynx and pharyngolarynx cancers managed by definitive radiotherapy.

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.