Circulatory disease mortality in the Massachusetts tuberculosis fluoroscopy cohort study

Abstract

High-dose ionizing radiation is associated with circulatory disease. Risks from lower-dose fractionated exposures, such as from diagnostic radiation procedures, remain unclear. In this study we aimed to ascertain the relationship between fractionated low-to-medium dose radiation exposure and circulatory disease mortality in a cohort of 13,568 tuberculosis patients in Massachusetts, some with fluoroscopy screenings, between 1916 and 1961 and follow-up until the end of 2002. Analysis of mortality was in relation to cumulative thyroid (cerebrovascular) or lung (all other circulatory disease) radiation dose via Poisson regression. Over the full dose range, there was no overall radiation-related excess risk of death from circulatory disease (n = 3221; excess relative risk/Gy -0.023; 95 % CI -0.067, 0.028; p = 0.3574). Risk was somewhat elevated in hypertensive heart disease (n = 89; excess relative risk/Gy 0.357; 95 % CI -0.043, 1.030, p = 0.0907) and slightly decreased in ischemic heart dis-ease (n = 1950; excess relative risk/Gy -0.077; 95 % CI -0.130, -0.012; p = 0.0211). However, under 0.5 Gy, there was a borderline significant increasing trend for all circulatory disease (excess relative risk/Gy 0.345; 95 % CI -0.032, 0.764; p = 0.0743) and for ischemic heart disease (excess relative risk/Gy 0.465; 95 % CI, -0.032, 1.034, p = 0.0682). Pneumolobectomy increased radiation-associated risk (excess relative risk/Gy 0.252; 95 % CI 0.024, 0.579). Fractionation of dose did not modify excess risk. In summary, we found no evidence of radiation-associated excess circulatory death risk overall, but there are indications of excess circulatory death risk at lower doses (<0.5 Gy). Although consistent with other radiation-exposed groups, the indications of higher risk at lower doses are unusual and should be confirmed against other data.

Radiation and circulatory disease

“…The two major studies of circulatory disease mortality in relation to medical diagnostic exposure are both of groups that received repeated fluoroscopic doses as part of the lung collapse treatment for tuberculosis (TB), in Canada [50] and in Massachusetts [51]. In both groups the lung dose was used as a surrogate for heart dose.…”

“…In the Massachusetts cohort there were additional analyses employing thyroid dose (a surrogate for dose to the carotid artery) and red bone marrow dose. As discussed by Little et al “one would expect carotid artery dose to be higher than thyroid dose, but that lung dose is probably lower than heart dose; estimates of both the heart and carotid dose may be wrong by a factor of 2” [51]. A novel finding in the Canadian data was a significant inverse dose rate effect for IHD, after adjustment for which the IHD dose-response was significant [50].…”

“…However, this was only the case when a 10-year lag was used; when 5- or 15-year lags were employed the effect ceased to be significant. There are no indications of such effects in the Massachusetts data, in which a 5-year lag was the default [51]. Although there is no dose-response overall in the Massachusetts data, if analysis is restricted to persons with < 0.5 Gy the dose response trends for all circulatory disease and IHD become much steeper, and borderline significant ( p =0.0743, p =0.0682, respectively) (Table 3).…”

“…In both cohorts there is limited medical and lifestyle information. This is more extensive in the Massachusetts data, and includes smoking and alcohol consumption, thoracoplasty, and pneumolobectomy; some of these variables were included in baseline models for certain disease endpoints [51]. …”

Low dose radiation and circulatory diseases: a brief narrative review

“…However, for exposures less than about 0.5 Gy, the balance shifts toward anti-inflammatory effects [11,40]. Interestingly, there is evidence of a steeper dose-response slope for various types of circulatory disease under 0.5 Gy in the US radiologic technologists [41], as also in two groups given highly fractionated fluoroscopic X-ray exposures [42,43].…”