The histopathologic basis for functional decrements in late radiation injury in diverse organs.

As more and more patients respond favorably to combined cancer therapies, the time of survival from radiotherapy will become the most important single factor in the incidence and progression of late radiation changes. The late sequelae of irradiation are the sum of the following: 1) residua of the direct and indirect early changes in responsive cell populations; 2) progressive vascular sclerosis with its associated effect upon connective tissue and the parenchymal cells; and 3) the reactive or replacement connective tissue proliferation which is responding to 1) and 2). From this it may be seen that further investigative efforts need direction toward: 1) reducing the magnitude and permanence of the early principal parenchymal cell injury; 2) diminishing the severity of the early microvascular change which adds significantly to the early parenchymal cell damage; 3) determining the mechanics of the progressive vascular sclerosis with a view to retarding this effect; and 4) lessening the reactive fibrosis.