Revision 1
March 19, 1998
by Radiation, Science, and Health, Inc.,
Edited by J. Muckerheide

1.2.3
Medical

1.2.3.2
Medical Patients

"There is strong evidence for a flattening of the dose-response curve at high doses in all of the cohorts except the CAN-TB series [Miller 1989], in which the curvature appears to be in the opposite direction, i.e, concave upward. It has been suggested that the flattening in the dose-response function at doses in excess of 4 Gy or so is the result of cell-killing effects. However it is unlikely that this curvature is solely a result of cell-killing since ... For the fluoroscopy cohorts (MASS-TB and CAN-TB) the doses were highly fractionated and it is unlikely that any single exposure involved doses which were high enough to cause appreciable cell-killing.

"Even when the women who received the highest doses are excluded, it is difficult to reach firm conclusions about the shape of the dose-response function at low doses. The incidence data provide weak evidence for a negative quadratic response (p= 0.1), while the Canadian mortality data indicate evidence for a positive quadratic component when the Nova Scotia data are included in the analyses. However, after allowing for this nonlinearity, a significant difference between the risk per unit dose in the two Canadian subcohorts remains. In contrast, if one allows for this subcohort difference, the quadratic component of the dose response is not statistically significant (p = 0.5). Based upon these analyses the Committee’s preferred models for breast cancer incidence and mortality are linear dose-response models."