Radiation-Induced Heart Disease

Abstract

That high doses of x irradiation can damage the heart and pericardium is common knowledge among radiotherapists and radiobiologists. A small number of case reports have described cardiac lesions following radiotherapy of thoracic cancer; the prevailing feeling, however, is that such complications are rare and relatively unimportant (1). The purpose of this report is to review 25 cases in which significant heart disease followed radiation therapy to the chest for a variety of malignant tumors. Study of this unique series of patients from a single institution has provided data on the relative frequency of the various clinical features encountered and their correlation with the radiation technics and doses used, as well as estimates of the incidence of this group of complications in an irradiated population. The importance of recognizing cardiac complications and differentiating them from the manifestations of advancing neoplasm is emphasized. A previous report (2) described in detail the clinical findings, hemodynamic studies, and pathological features of the first 21 patients of the series; these will be briefly summarized in the following paragraphs. This paper adds 4 new cases and presents the radiation dosimetry and incidence calculations in greater detail. Selection of Patients The cases all came to our attention after the development of significant clinical heart disease or when the lesions were discovered at autopsy. The 25 cases included 12 of Hodgkin's disease, 5 of breast carcinoma, and 8 with a variety of other tumors. None of the patients had evidence of heart disease before treatment was begun, and no patient was included in the study whose heart disease appeared to be due to tumor involvement. Technics of Radiotherapy The radiation was fractionated so that weekly doses of 500–1,250 rads were delivered in four or five daily sessions. None of the patients received massive single doses or unusually rapid fractionation such as in the cases of radiation heart disease reported by Rubin et al. (3) and Blumenfeld and Thomas (4). Of the 21 cases treated at Stanford, the majority received supervoltage irradiation from one of the two linear accelerators operating at peak voltages of 5–6 MeV. The beam characteristics are similar for these machines and have been described previously (5, 6). There is a build-up of dose after entry, with the maximum reached at a depth of 1 to 1.5 cm in tissue. The small focal spot and efficient collimation result in negligible penumbra. Under conditions of operation the beam is flat and has minimal low-energy scatter or contamination. Most treatments are given at 100 cm SSD at 80–250 rads per minute at the maximum. When field sizes larger than 30 X 30 cm are required, treatment distances are increased. Therapy with equally weighted opposed fields results in homogeneous dose throughout the treated volume, as shown in Figure 1.